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Cheap petabyte mass memory for computers

Optical disc or magneto optical disc or magnetic tape can be used in computer mass memory. But only semiconductor memory is the one that is having all recognition. But semiconductor memory is still costly, petabyte of memory in its cheapest semiconductor form costs 11 000 - 12 000 dollars. That was before nowdays chip dire straits so now it probably costs more. Optical disc costs almost nothing to make, CD or DVD or Bluray discs mass order from direct from factory in China is just few cents / pennies per disc. Magneto-optical disc too is cheap. VHS video cassettes from China cost less than one dollar sometimes, although VHS players are rare nowdays. So magnetic tape is not expensive at all when it is produced in suitable numbers.
LTO tape is used in mass memory in data centers. It has 18 terabyte capacity in small cassette. If it would be produced as mass produced consumer product, its price per cassette would be as low as VHS cassette. With 18 terabyte capacity. About 50 dollars for petabyte memory is much cheaper than 11 000 dollars. And LTO cassette can be used other duties too and not just PC mass memory. It can be analog audio cassette, 600 m tape length with 9 micron tape (when compared to 1035 m of thinner tape that fits in LTO cassette), much more tape length than C-cassette, so much higher tape speeds can be used, and tape is half inch (12,7 mm) thick so very good analog sound quality. Also tape formula development, grain size of metallic particles and metallic compounds used in tape, are better than in C-cassette. So CD quality multitrack (surround sound) analog audio is possible with or without noise shaping. Also LTO cassette can be used as video cassette, either digital or analog video. 18 terabytes is really high quality video for feature film. Or it can be used as analog video cassette, digital video compression makes information of video stream compressed to one thousandth sometimes, but analog videotape is mostly uncompressed. so now video has thousand times more information than highly compressed digital video.
All three, digital memory / digital video, analog audio, and analog video can be in one consumer grade LTO tape player, so LTO cassette can be used for all those duties. This consumer LTO tape player / recorder / PC mass memory drive when mass produced is not so expensive, price is like old VHS players had, but now device is much more versatile when same size standard cassette can be used both PC mass memory, videocassette (with both digital and analog form if needed, or just digital video), and analog audio tape. LTO cassette may be the same but tape inside cassette may be different when digital memory, digital video, and analog audio is used. Analog video may be surplus, so it can be left out if things get too complicated.
Slightly larger LTO cassettes can be made, magnetic tape is cheap so why not use it. CD cases have diameter of 125 X 142 mm, bit in digipak cases sizes like 150 X 150 mm is used. If LTO cassette has about 152-153 mm X 160 mm size, (6 X 6,3 inches) it fits in its 153 mm side in CD record bins in shops, although it is 160 mm tall, and about 2 cm thick when CD case is 1 cm (10 mm) thick, so one LTO cassette takes the place of two CDs. But now LTO cassettes can be sold in shops that sell CDs, with ease. Now this version of LTO cassette has about 2,4 times tape length of smaller standard LTO cassette used in data centers. So capacity is about 43 terabytes.
Old VHS cassettes had “library case” style package with extended edges / hub, size was 11,625 inches (295 mm) or about 11,2 inches (285 mm). Largest VHS case that I have seen is 221 mm, but those large VHS cases were used in 1980s and are manufactured even today. Now LTO cassette can be the size of VHS cassette case, so 295 X 300 mm or 285 X 290 mm about, tape capacity is about 9 times of normal small LTO cassette. Tape can be 1 inch (25,4 mm) width too, not 1/2 inch type, cassette is not much thicker than normal LTO cassette anyhow, and capacity doubles. Now capacity is about 330 terabytes in VHS case dimension size cassette, although LTO is cassette is square size so all sides almost equal. But magnetic tape is cheap. So 330 terabytes in old VHS case size package. And those 330 terabytes are cheap.
Even petabyte size LTO cassette can be made, it must use 2 inch (51 mm) tape and tape spool is about 14 inch (356 mm) size, so “cassette” is about 360 mm X 365 mm, hefty fine. Old DVI videocassettes that professional television broadcasters used, had largest size 36 cm videocassette, so this LTO cassette is same size. Who needs petabyte size LTO cassette? Data centers when using normal LTO must use 56 LTO cassettes if petabyte capacity is needed. Those LTO cassettes are inside large wall of LTO drives, and perhaps robotic system loads and unloads LTO cassettes. This system is expensive, 100 000 - 1000 000 dollars? Now just one LTO drive is needed for petabyte capacity, cost saving is enormous when compared to larger system. And data centers need several petabytes of “cold” memory storage, so for example 5 petabytes needs almost 300 small LTO cassettes and their wall to wall robotic loading system, 10 petabytes is 560 small LTO cassettes etc., when one cassette hold one petabyte (1000 terabytes), only 5 or 10 LTO drives are needed, and cost and size savings are enormous. Magnetic tape itself is cheap, when magnetic tape is mass produced as (home) consumer product, like C-cassette or VHS cassette tape, it is drive systems that are costly. When tape is 2 inch thick it is four times faster search time than in 1/2 inch thick tape, although tape spool is huge in petabyte “cassette” so no gain in search speed.
Optical disc is super cheap, archival disc is optical mass memory based in Bluray, it has three layers and 150 + 150 GB capacity (two sided disc). If it uses four layers it would be slightly less than 200 GB per side, like four layer Bluray has fourth layer slightly less capacity than previous three layers, so similar archival disc is about 390 GB or so (two sided disc)?
Cheap “Discman” type made CD players are made in China, price is 5 dollars or even less per CD or DVD Discman player, price covers electric motor, laser pickup, electronics etc. needed. If there would be 100 petabyte optical drive, it uses about 256 optical archival discs of 120 mm diameter, stacked in a “tree” of 256 platters stacked vertically like old computer magnetic platters in data centers or modern hard drives that have platters stacked too. Those 256 platters have each individual electric motors and laser pickups, so each disc can rotate individually, and also discs can be changed individually, so there is connector / disconnector in each motor / pickup / disc combination so that disc can be taken away from “tree” of 256 discs and replaced manually when needed. this 256 disc platter tree is one optical drive, about 1,35 - 1,5 m tall if space between discs is only 5 mm or so, and perhaps 30 X 20 cm wide so very small. Price is perhaps 1000 - 1500 dollars (Discman price per platter). That is for 100 terabyte memory. Petabyte needs 10 such platter-tree drives. Cost is 10 000 - 15 000 dollars. So no advantage over cheapest semiconductor memory of petabyte. But the individual discs cost almost nothing, 2560 optical discs is only about 100 dollars or so (mass order from China). 100 dollars is much less than 11 000 dollars. And no need to wipe out old information when new information is loaded, disc is just taken away from platter tree and put to paper sleeve and then transferred to archive. If archive is full discarded discs can go to recycling center that accepts CD, DVD, and other types of optical discs. They can be recycled, although recycling is more difficult than for example plastic bags. The cost of semiconductor memory demands that information must be wiped out when new information is loaded, therefore “cold” memory storage like LTO tapes and archival disc.
But when memory is really cheap, it can be used as regular computer memory, challenging expensive semiconductor memory. Search time is longer, but when memory is super cheap, that does not matter.
For example platter tree system of 256 optical discs can be in office job PCs, or connected to any PC that is used for work, not in home PCs. Archival disc is write once type, but also write many times type disc can be used that uses Bluray standard, capacity is now about two thirds of archival disc. But those optical discs cost almost nothing.
Home PC can use small platter tree that has only 12 discs, in one frame of about 6 X 12 cm size without individual electric motors in each platter.
There can be several laser pickups per disc side in optical drive because laser pickups are cheap, now information search is very fast.
Home PC with optical drive of 12 platter disc frame has about 4,65 terabyte capacity so it is about 1000 times more than DVD disc one layer. And costs almost nothing. Now video feature films can have 4,65 terabytes accuracy so less video compression needed.
Larger discs can be used, 152 mm (6 inch) is about 625 GB capacity, if 16 platters are in frame that is 10 terabytes. 203 mm (8 inch) disc is 1,115 terabytes so 18 platters is 20 terabytes.
If Bluray discs are used instead of Archival disc format that makes about 2/3 capacity. Optical drive can use both Archival disc format and Blurays.
Old magneto-optical discs had 14 inch large format used in data centers in sometimes (late 1980s / early 1990s?). There can be 410 mm (16,1 inch) optical disc format, 4,55 terabytes per platter, so about 220 such discs in platter tree is one petabyte. Size is not much bigger than smaller system that uses 256 smaller 120 mm discs. But now capacity is 10 times bigger when bigger discs are used. Again this 220 X 410 mm platters optical drive can be used with office PCs and with any PC that is used in work. Now every PC that is used for work can have own super cheap petabyte mass memory. Each 410 mm disc has almost 1000 times capacity of one layer DVD disc. Making optical discs costs almost nothing per disc (when mass manufactured). Situation is same like with magnetic tape, mass manufacturing puts price to extremely low per item (tape cassette or optical disc). Semiconductor memory, although manufactured billions of units, still costs over 10 000 dollars per petabyte.
Why petabyte memory is needed? Virtual reality needs millions or billions of pixels, and holographic video too. And video picture, if it is in virtual reality or holographic form, is linear, it moves from A to B and does not jump from place to place like random access memory, so magnetic tapes and optical discs can be used to present virtual reality movies and holographic movies with great accuracy. And any type of media or computer program which is in linear form and does not require jumping back and forth like PC hard drive does. But optical disc memory can be very fast too if several (cheap) laser pickups are used in each disc side.
Magneto-optical disc is one opportunity, it can perhaps store analog information (analog audio or analog video) easily.
So home PCs (and also PCs used in workplaces) can have very high capacity memory that costs almost nothing. Terabytes of memory with only few dollars cost. Why this opportunity is not used. Why with home PCs have not offered those high capacity optical / magneto-optical or tape drives?.
The difference in price is so huge when optical disc or magnetic tape is compared to semiconductor memory, it must be used for good.

It is possible to build “tree” with optical disc platters that are used like platters in hard disc. If those optical disc platters had their own individual electric motor those discs could all spin individually so search / write speed would be very fast. How to make this happen? Perhaps simplest is sort of “belt drive” where belt from electric motor is connected to outer edge of optical disc, when in contact with disc edge this belt spins optical disc. Those belt drive systems are used in car engines to drive start motor, car electric dynamo etc. Similar belt that goes from electric motor to optical disc outer edge can be used. Perhaps also axle of the “tree” holding vertically stacked optical discs can hold many electric motors. CD / DVD / Bluray has 21 mm central area, if small electric motor and its gear that spins disc is 21 mm diameter and slim enough, about 5-10 mm tall, it can be in the middle of the disc. If the whole 21 mm area that disc has is hole where electric motor fits, this small area that is otherwise just plastic, 1,2 mm thick, can also be used by electric motor and its gear. Or electric motor and gear can be wider than 21mm but then it takes room from laser pickup and separation of discs must then be taller. Or all electric motors are outside of the “tree” axle, and they just spin numerous axles that are each inside each other, so that smallest diameter axle is in the top of the the “tree” and larges axle in the bottom, smallest axle in the top spins top disc and larges axle the disc in bottom, and various sizes of axles spin disc in between. Perhaps 12- 26 axles fits in 21mm diameter, axles inside each other that do not touch each other because they spin in varying speeds, so axles must be thin. Now each disc, 12 - 26 discs, must have each different size hole where its axle fits and spins this particular disc, so optical discs must then be manufactured at 12 - 26 different central hole sizes.
Chinese Discman CD / DVD player is cheap, so those individual optical disc spinning systems in “tree” are also. If this tree has 256 stacked optical discs, and separation from disc to disc is 10 mm, tree is over 2,5 m high, which is lot if and when discs must be loaded manually.
There is “Ecodisc” optical disc manufacturing method that makes disc not only cheaper, but also only half thickness of normal CD or DVD, and also manufacturing is eco friendly, no harmful chemicals used.
Perhaps roll to roll printing methods that are used in printed electronics, can be used in optical or magneto-optical disc manufacturing. Ecodisc is flexible optical disc, it can be bend. This optical memory disc technology needs two-sided discs. Roll to roll printing can make blank write once - or write many times - type discs, blank discs without written optical pits. Now price of optical disc or magneto-optical disc that was low already is even lower. Even large size discs can be manufactured at very cheap price then.
Putting optical discs (or magneto-optical) in protective cartridge error correction does not have to be used, and disc capacity increases, there was “Dataplay” format of optical disc that was miniature size. But with cartridge around disc system becomes complicated and even taller when multiple discs should be stacked.
Ordinary home PC can have LTO tape drive that has cassette size of old VHS library case with extended edges, 285 or 295 mm tall, so cassette is about 280 -285 mm or 290 - 295 mm square size, packed in simple cardboard package like blank VHS cassettes. Also size is now like VHS case with extended edges. Capacity is about 330 terabytes in maximum (9 X tape spool capacity of normal LTO tape, and tape is 1 inch thick not 1/2 inch), but different tape lengths can be used like in VHS tapes. When ordered from China in large quantity direct factory order price is perhaps about 20 dollars per blank 330 terabyte full tape length LTO cassette, when comparison to VHS cassette is made which has about same size tape spool which is in normal LTO tape which has about 10 X 10 cm diameter cartridge cassette.
Also smaller CD case size LTO cassettes can be made that have 2,4 times capacity of normal LTO cassette.
Office/work PC can have 256 disc tall system that can use both 120 mm optical discs and also 380 mm / 15 inch optical discs, both use same “tree” and electric motors, laser pickups etc., only diameter of optical disc varies. When used with 120 mm discs capacity of 256 disc system is 100 terabytes, when used with 380 mm discs capacity is one petabyte. Price perhaps is between 1000 and 2000 dollars with this optical drive, but optical disc platters cost almost nothing.
Smaller version of this system can be used in home PCs, 26 optical disc platters either 120 mm or 380 mm size, like in office PC user can freely change disc platter size, it works with any size discs between 120 mm and 380 mm. All 26 disc platters have their own electric motors etc. individually. Price is about 100 - 150 dollars of this kind of optical drive and capacity is either 10 terabytes with 120 mm discs and 100 terabytes with 380 mm discs. Home PCs can also have smaller systems like 18 X 203 mm size discs and now 20 terabytes in smaller space, or simply 12 X 120 mm discs and optical drive has not individual electric motor for each disc so system is now compact and simple and cheap, and can fit perhaps (120 mm X 60 - 70 mm disc package frame) in laptop PC. Capacity is about 4,65 terabytes.
If Bluray technology is used in write many times- discs, capacity is perhaps only half of Archival disc capacity, or modified Bluray that can have 128 GB write many times discs (256 Gb in two sided disc) so now 2/3 of Archival disc capacity.

If optical or magneto-optical disc is used as PC mass memory, it is possible to stack those discs as a “tree” of discs, so that every disc has its own motor and laser pickups. Or simply use many separate disc drives as RAID - type memory. Chinese “Discman” CD / DVD players cost only few dollars when ordered at large quantities straight from factory. So for example 256 disc optical or magneto-optical RAID system is not so expensive if one optical drive costs only few dollars. It is possible that office / work PC has optical RAID of 256 discs and capacity of 100 terabytes when 120 mm discs are used and one petabyte capacity when 380 mm discs are used. It is possible that same RAID station can use different size of optical or magneto-optical discs, for example 120 mm, 203 mm and 380 mm, user can choose what size disc to use, in disc drive that is large enough for 380 mm disc can smaller discs like 203 mm or 120 mm be used. This kind of optical 256 disc drive can even be used with high performance home PCs. So home PC then has petabyte optical mass memory. Because laser pickups are so cheap it is possible that there are many laser pickups per each disc side (discs are two-sided). Making two-sided discs with “Ecodsic” CD / DVD manufacturing method halves disc thickness and makes discs cheaper. Also roll to roll manufacturing like in printed electronics can perhaps be used to make optical or magneto-optical discs, blank discs without written information (so they are then write-only or write many times- discs).
If optical discs are stacked in a “tree” and they all have individual electric motors and laser pickups, but power of motor must be transmitted to disc in a “tree”. Belt drive or chain drice can be used, belt or chain connected either to outer edge of disc or central axle that spins the disc. When chain drive is used in outer edge of disc there is soft rubber ring connected to disc and this ring is connected to chain that spins the disc. Axle drive can be used, thin metal stick is axle connected to motor, axle goes from sideways outside disc to central axle of the disc itself and 90 degree turn is made using teeths in the two axles, “worm drive” or worm gear, used in old trucks, is one method how to turn axles 90 degrees, so worm gear / drive can be used in optical disc system that needs to be powered off-axle. When stacked in a “tree” each disc can be changed indidividually so lock/unlock mechanism is in each disc / motor / laser pickup combination so that discs can be individually taken out from the tree, “tree” is “cut” during disc change which is done manually, vertical disc tree is turned to horisontal position to some supporting platform and then “cut” when disc is changed and after change has been done “cut” part is connected to “tree” again and tree lifted to vertical position. If discs and their drives are stacked in a tree form floor space is minimized, but if distance between discs is 10 mm, disc tree is over 2,5 m high. So two trees of 128 discs is shorter, but more floor space is now needed. Cost of 256 disc optical drive may be over 1000 dollars, but optical discs themselves cost almost nothing when mass manufactured, so one petabyte or 100 terabyte mass memory then becomes several petabytes or multiple X 100 terabytes mass memory for PC when discs are changed. No need to wipe out old discs, because they are cheap, discs are put to paper sleeves and are archived when are not used in optical drive. Magneto-optical discs are one option for super-cheap mass memory.
Also magnetic tape can be used, not as cheap as optical discs but tape is still enormously cheaper than semiconductor memory when mass manufactured in large quantities (think old VHS tapes and their minimal cost when mass manufactured).
Even laptop PC can use these, small pack of 12 X 120 mm optical or magneto optical discs, as Archival discs 4 layers per side (about 390 GB in two sided disc, when fourth layer has slightly less capacity than previous three layers), 4,65 terabyte capacity if in 12 X 120 mm disc frame, no individual motors per disc needed, but many laser pickups can be used because they are so cheap, one optical drive can handle either just one 120 mm Bluray or Archival disc, two sided, or full pack of 12 X 120 mm discs in one “tree” frame that is perhaps 60 mm thick.
So now in laptop can be used CD-, DVD-, Bluray- or Archival disc, the disc bay is about 60 mm deep, there can be put one CD or DVD or Bluray disc, or there can be put full pack of 6 X 120 mm discs in a frame “tree”.
Also this same laptop PC can have LTO tape drive, (take up reel inside laptop PC), 10 X 10 cm wide LTO cassette cartridge has 18 terabytes capacity, that is super cheap compared to 18 terabytes in USB memory sticks.
Desktop PCs can have RAID station that is made from individual cheap chinese Discman type CD / DVD players modified to use Bluray/Archival disc standard and read/write lasers. 256 those Discman players are in 16 X 16 arrangement stacked in a box in a wall, when disc is changed Discman player is pulled forward from 16X16 Discman box frame and cover of player opened and disc changed. Bad thing about this is that two sided discs cannot be read or written simultaneously, disc must be manually turned when other side of disc is used. But also now individual Discman players can be used as portable Bluray players, there is 256 of them in a box, so whole family can now have own portable Bluray player if they want some, and then they can put back them to RAID box frame of 256 of them when not needed. Capacity is 100 terabytes in 256 X 120 mm discs.
Larger discs can be used in specially build optical RAID station, capacity is 100 terabytes with 26 X 380 mm (15 inch) discs, and 26 X 380 mm discs is still fairly small unit so suitable for PC. This optical disc mass memory can system can use smaller discs, like 120 mm or 203 mm in same 380 mm diameter disc bay. If 256 discs of 380 mm diameter are used in larger system capacity is one petabyte. Discs are in tall “tree” so that floor space is minimized in this large system. One 380 mm disc is 3,9 terabytes.
Price is perhaps only 150 dollars for 26 X 380 mm disc mass memory drive (when compared to Discman price, price of about 26 Discman players). But optical discs themselves cost almost nothing.
Terabyte and petabyte are here counted as 1000 gigabytes and 1000 terabytes, not 1024, Bluray and DVD use similar 1000 not 1024 counting when their capacity is referred.
If Discman players with Bluray/Archival disc capability is used, less than 256 player RAID boxes can be used with PC. For example 64 or 36 Discman players as PC mass memory.
Desktop Pc s can also have LTO tape drive that uses cassette which is size of “VHS library case with extended edges”, old VHS videocassette in a case- sized. Those extended edge cases are about 285 or 285 mm tall. One LTO cassette that is square 285 - 295 mm (because LTO cassette has only one tape reel, takeup reel is inside tape drive) and packed in cardboard case like blank VHS tapes. If tape width is one inch capacity is about 330 terabytes, and if tape is 35 mm width (used in magnetic tapes of film sound editing, before digital sound took over) without holes in the edges that film sound editing tapes had, this 35 mm magnetic tape has 450 terabytes capacity in 285 - 295 mm VHS library case sized cassette. 35 mm tape makes cassette wider than with 25,4 mm one inch tape, but it is still reasonably size when compared to old VHS library cases. Magnetic tape is cheap when mass produced like VHS tapes. Now PC has both 450 terabyte tape memory and 100 terabyte optical memmory. Cassette of max. 330 or 450 terabytes capacity is only maxumum capacity that fits in cassette, shorter tape lengths can be used so that LTO cassette is cheaper and when maximum capacity is not needed. Smaller LTO cartridge would be about CD case sized 152mm/153mm X 160mm LTO cassette with 1/2 inch tape. This has about 43 - 45 terabytes capacity.
If someone wants 330 terabytes in 1 terabyte USB memory sticks that will be 330 USB sticks with price of 50 - 25 dollars each. Cost is 8200 - 16 500 dollars. This same capacity can be in one LTO cassette that costs between 20 - 100 dollars. Cost saving is 16 400 - 8100 dollars. And of course another LTO cassette can be bought, and now cost saving doubles etc. Optical disc memory is even cheaper. And magneto-optical disc too. And when someone tries to find where in those 330 USB sticks is some specific information that is searched, one LTO cassette has find it already when someone is plugging all those 330 USB memory sticks trying to remember which one of those 330 USB memory sticks it was that had information that is searched.

It is possible to build exabyte data store, and it is even extremely cheap, if optical or magnetic tape memory is used. Optical discs are cheap, if made from roll to roll manufacturing like printed electronics, blank optical discs without pits for laser, write once or write many times- types, and magneto-optical discs can be made also. In late 1980s or early 1990s was 14 inch magneto-optical disc platters in data centers.
Exabyte data store can be 10 000 optical disc drives that have each 100 terabytes (or 104,876 terabytes) optical disc, two sided, so disc is 193 cm (76 inch) sized and uses four layer Archival disc technology (nowdays Archival disc uses only three layers, but four layer BDXL Blurays have been made and Archival disc is based on Bluray).
193 cm disc seems to be absurdly large but optical discs themselves are cheap, what is costly in optical drive is spinning system (electric motor) and and electronics of optical disc drive. In China is Discman portable players made that cost few dollars. Laser pickups are actually cheap, so this big 193 cm optical disc can have dozens of laser pickups in each side of disc. Those 193 cm disc optical drives are stacked in a tree form, 250 optical disc drives in a tree, about 3,5 m height. Floor space needed per 250 disc drive tree is about 2 X 2 meters. 40 such drive trees are one exabyte (is exabyte counted as 1000 terabytes or 1024 terabytes or 1048,76 terabytes or more etc.).
This exabyte data store is extremely compact. It is also cheap, although discs are almost 2 meter diameter, it is just another optical disc player, like giant Discman CD player. So cost of 10 000 optical disc drives is how much compared to 10 000 ordinary Discman portable players? The system of operation and components are almost exactly same, only several dozen laser pickups are in 193 cm optical disc drive instead of just one in Discman. Both are mass manufactured products, 193 cm optical disc drive and Discman. Both are almost the same, only disc size is different. If mass manufactured optical disc drive of 193 cm disc cost 50 dollar (and not less than 5 dollar like Discman), 10 000 of them is 500 000 dollars. There is also robotic loading system that changes discs and takes old discs to disc store and brings new discs to optical drives. Distance between optical drive tree-rows is 2 m so that robotic system can move and load 193 cm discs. Optical discs themselves are cheap, so this exabyte capacity means only capacity that is always in use, there can be tens of thousands optical discs in data disc store room, so that capacity can be several exabytes, or several dozen exabytes, every optical disc, roll to roll printing manufactured, costs only few dollars or less than dollar.
Magneto optical discs can also be used.
Also is possible that discs have no error correction so that information space is larger, like old DataPlay discs had. Discs are enclosed in plastic “Minigrip” bags about 2 m size in data store room and when robotic system loads disc to optical drive it opens Minigrip bag and loads disc to drive, disc is few seconds only exposed to air outside disc drive. “Cleanroom” environment that semiconductor factories have can be in data store.
Larger system would be zettabyte optical data store, 1000 X larger than exabyte data store. So that is all internet in the world in place Cost is about 500 million dollars plus something.
Also magnetic tapes can be used, petabyte LTO tape would be about 36 cm diameter cassette with 2 inch (51mm) tape. 1000 or 1024 such tape drives is in exabyte data center. If cost per tape drive is about 200 dollar, tape drive is not so different like VHS player, mass manufactured tape drive. 1000 of them is 200 000 dollars for exabyte data store. But again, tapes can be changed so actual capacity depends on how much LTO cassettes there are in data store s store room where LTO cassettes that are not inside tape drive are held. So it is many-exabyte data center.
Magnetic tape is cheap, when mass manufactured in large numbers, like VHS tape, cost of VHS cassette is one dollar or less in China, both tape inside cassette and cassette itself. Spool of about 14 inch / 356 mm diameter 2 inch tape is higher, but still extremely cheap petabyte compared to semiconductor memory.
Zettabyte data store is then about 200 million dollar cost, for whole internet in one room, if petabyte LTO tape drives are used.

Things like optical discs or magneto-optical discs are cheap, and magnetic tape is cheap also when mass produced. Somehow when these super-cheap mass memories are used, mass memory manufacturers make them for some odd reason super-expensive systems, when LTO drives and optical Archival discs are sold as large system with their robotic loaders, and price is million dollar or so. It is like manufacturers of those mass memory systems have somehow forgot the laws of capitalism, the most illogical thing to do when you have super cheap product, like optical disc that costs almost nothing to make, and magnetic tape, worst thing that you can do is to make some super-cheap product to be super-expensive, which is the way the makers of Archival disc and LTO tape drives sell their product, somehow they managed to turn those super-cheap and easily mass produced produced things that can produced cheaply millions of units, to expensive niche products, aimed for exclusive customers at high price.
No wonder that LTO tape drives are sold less and less by each year, and Archival disc has not been particularly successful. Earlier 1970s Sony and JVC made first commercially successful VHS video tapes and recorders, to exploit cheap mass produced magnetic tape. Sony was in DVD and Bluray business from the beginning. But somehow marketing departments of those firms that make optical disc memory and LTO tape have lost the point. If you have product that has enormous advantage over other mass memory products in price, like optical disc has over semiconductor memory, logical thing is that this cheapness is used to make mass memory successful product that is mass marketed and mass manufactured, like VHS video cassette was made to be consumer product to home users as consumer product. Earlier videotape was for professional use only. But now when home PC users need cheap mass memory, manufacturers of both optical disc and magnetic tape memory have made their products only for data centers. When you have super-cheap product, you don t turn it to super-expensive product, because then it loses competition advantage in free market. Somehow makers of optical mass memory and tape memory have completely lost the fact that optical disc is enormously cheaper compared to semiconductor memory, and magnetic tape too, although tape is not so ultra-cheap that optical disc is. But this enormous price advantage over semiconductor memory is not used. If LTO tapes and optical discs were mass manufactured consumer products their success would be huge, optical disc just needs to have larger amount of data than 300 GB that it has now, but this is easily to be made when discs are larger than nowdays small 120 mm discs or discs are in packs of stacked discs in a “tree”. Price is not a problem.
VHS or Betamax tapes were not made to be expensive products, million dollar large TV broadcast systems made for only TV broadcast stations, they were made to be cheap consumer products. If VHS or Betamax would have been million dollar TV broadcast systems, competing with U-matic and open reel videotape, VHS and Betamax would have been commercial flop. But that is exactly what have been made of LTO tape memories and optical disc memory. LTO tape cassette is practically one half of VHS cassette without takeup reel (which is inside tape drive). VHS cassettes are sold in 1 dollar price or so in China. And somehow this actually super-cheap mass memory of 18 terabytes have been turned to expensive million dollar system for data centers only, where it must compete with expensive semiconductor memory products It makes no sense. Every home PC welcomes cheap 18 terabyte mass memory. It can be used for distributing 3D Hollywood films with almost studio quality with minimal video compression, 4K or 8K films or 360 degree virtual reality environments- and films. It can also be used as multitrack surround sound analog audio tape for analog purists, much higher quality than C-cassette or vinyl LP.
Optical disc too have enormous economics of scale advantage over semiconductor memory, more amount of memory, the bigger price advantage is. 300 GB in USB memory stick and same amount in optical disc makes not so big difference, but when there is 300 terabytes, price advantage is enormous, 300 USB memory sticks with 1 terabyte each is about 7500 - 15 000 dollars. 300 terabytes in optical disc is perhaps 100 dollars in disc prices (or far less) if discs are large enough and there is lots of them. So there is 100 dollar versus 7500 - 15 000 dollars price advantage. Makers of optical disc drives have completely forgotten this huge price advantage.
If home PC has about optical disc drive that 78 - 80 two-sided optical discs in a “tree”, each disc has its own electric motor and laser pickups (many of them per disc side), and discs are 380 mm diameter (15 inch), four layer per disc side version of Archival disc (in 120 mm disc that is about 390 GB) 380 mm disc is then 3,9 TB per disc, and 78 - 80 them is 300 terabytes. LTO tapes are data compressed, so optical discs can be too, about 3,3 X data compression, so now this pack of optical discs is one petabyte. So now home PC has optical drive that has 1 petabyte in compressed and 300 terabytes in uncompressed form.
LTO tapes are data compressed, so if some modern data compression codec is used (modern data compression codecs are compilation of several different data compression methods that selects best of them according to data that is compressed) perhaps 4,4 X compression is possible, LTO tapes are slow compared to other mass memories. so slow data compression / decompression is possible. If instead of mini-size LTO cassette of 10 X 10 cm and 18 terabyte capacity, LTO cassette is size of VHS library case with extended edges, about 285 - 295 mm tall (and square in size, LTO cassette has only one reel not two like VHS cassette), and tape width is 35 mm, now about 450 terabytes fit in LTO cassette uncompressed. 4,4 X compressed that is 2 petabytes. That is 2 petabytes in about the same size that is in VHS videocassette library case with extended edges, and slightly wider. Cost is perhaps anything between 20 to 100 dollars per full tape length LTO cassette. Smaller tape lengths have smaller price.
Home PC can have both optical drive of 300 TB and tape drive of 450 TB, outside PC case, not inside like mass memories like DVD-ROM drive or hard disc is. 78 disc optical drive is not so different like 78 Discman DVD/CD players, so price is around 400-500 dollars for 300 terabyte optical disc drive. Discs themselves cost almost nothing, unlike USB memory stick which at cheapest cost 25 - 50 dollar if one piece of one terabyte USB stick is bought. And pack of 78 - 80 optical discs that are 380 mm size is also manageable size optical drive, although each disc has its own electric motor and laser pickups “tree” is small enough that it fits in a table, about 1,2 m or 1,5 m tall perhaps, but it can be in a floor too. LTO tape drive with 450 TB cassette needs less space although takeup reel is inside tape drive. Price of that tape drive is perhaps 100 - 200 dollars when it is mass produced product manufactured in millions of units like hard disc drives. Larger petabyte LTO cassette (about 36 cm - 37 cm diameter) can be made for data centers, with 2 inch (51mm) tape width. When data compressed 1 petabyte becomes 4,4 petabytes. In home use most of those 450 TB LTO cassettes are perhaps used for films like Bluray discs are used today, but 450 TB is much more than is needed so no maximum tape length in those cassettes. LTO if it uses 4,4 X compression automatically can use then 4,4 X lossless compressed (average compression ratio, may vary) video when compressed video is in LTO compression format.
Most of internet usage is in Netflix type video streaming and Spotify type audios streaming, it is linear data, film goes from beginning to end, and Youtube video too, and song also, so linear data storage like magnetic tape or optical disc suits for it.
So digital films and video / virtual reality games can now be seen without visible video compression artifacts, and practically endless pixel rate, 8K, 16K or whatever 3D virtual reality experience demands, and at super cheap price, in home, so truly “home theater experience” is possible. LTO tape if its 35 mm wide can be used to record and playback up to 48 analog audio tapes at studio quality multitrack surround sound, so in home can be 48 track super high quality analog sound “Dolby Atmos” style surround sound system. In analog sound recording 35 mm wide tape in LTO cassette of 285 mm - 295 mm size can also be used, 48 tracks maximum One studio tape recorder in 1980s used 1 inch (25,4 mm) tape and 32 tracks, so 48 audio tracks should be possible in 35 mm tape. Smaller amount of tracks tape recorder is also possible, like 36 or 32 tracks in 35 mm tape if analog sound is recorded.
203 mm optical disc drive that has 18 discs in tree and each have own motor, and this optical drive can be carried so it is portable, capacity is 20 terabytes, and this portable small box box carried using carrying handle in the box can be plugged to smartphone or tablet PC. Other 203 mm discs are in plastic bag, discs closed in paper sleeves, 27 extra discs in plastic bag, so now 50 terabytes available in portable form when both are carried, 50 terabytes super cheap mass memory connected to smartphone or tablet PC. 50 one terabyte USB sticks cost about 1250 dollars to 2500 dollars, and those optical discs almost nothing.
203 mm optical disc is about 1,115 terabytes if 120 mm disc is 390 gigabytes. The 20 terabyte portable optical mass memory is small box of about 21 X 21 X 25 cm, “tree” of 18 discs fit inside, each disc has individual electric motor and laser pickups, several laser pickups per disc. Box is top loaded like large Discman player, from hatch. There is carrying handle that swings to the the side when not needed. If compression ratio is 3,3 X then it is about 65 terabytes compressed data (data compression rates are always average). 27 other 203 mm discs are in plastic bag in their own paper sleeves, 45 discs in optical drive and in bag together is 50 terabytes uncompressed and 165 TB compressed data. If more data is needed (optical discs cost almost nothing) plastic case, like small suitcase with carrying handle, can have 72 discs and when 18 discs are in optical drive total 90 discs, about 100 terabytes uncompressed and 330 TB compressed. The small plastic suitcase is so small it can be inside bigger real suitcase if someone is travelling with 72 spare optical discs. Travelling with 50 or 100 one terabyte USB memory sticks require room too and USB sticks have weight too. 100 USB memory sticks with 1 TB capacity each cost 2500 dollars to 5000 dollars, optical discs almost nothing. The optical drive box with 18 X disc tree of 203 mm / 8 inch discs is practically 18 X discman player, about 100 dollar perhaps or slightly more is price of this portable optical disc drive that can be ported to smartphone or tablet PC. So cost of two to four 1 terabyte USB memory sticks cover cost of this optical drive, and optical discs cost almost nothing. So super cheap portable 50 or 100 terabyte (uncompressed) mass memory.
If LTO tape is in about CD case sized cassette, 152/153 mm X 160 mm, CD case is 142 mm but some digipak cases are 150 X 150 mm or even bigger, This LTO has capacity of 43 or 45 terabytes uncompressed. If compression is 4,4 X then about 200 terabytes is available in CD case size LTO cassette, it is about 20 mm thick with 1/2 inch tape, two times thickness of LTO cassette compared to CD case which is 10 mm. This about CD case sized cassette can be used in portable LTO tape drive, connected to smartphone or tablet PC. Tape cassette and tape drive are quite small, even when takeup reel is inside tape drive.
Large discs in data centers that can be 100 terabyte or more, 100 TB or 104,576 TB (1024 megabyte X 1024 gigabyte) fit in 193 cm diameter 76 inch disc, if compared to 12 cm 390 gigabyte disc. If those discs have no error correction lot more data fit to those discs, like Dataplay dics that were small size but high capacity. Plastic protective cartridge can be with those large discs, like earliest Bluray discs had protective cartridges. But not so many laser pickups can now be used, perhaps only three per disc side? The cost of that cartridge is not so much perhaps, CD jewelcases are sold in China that cost almost nothing when ordered large quantities straight from factory, like optical discs cost almost nothing. So if 193 cm disc needs protective cartridge that is not so much increase in cost. But perhaps increase in size is bigger problem, although plastic case of almost 2 m size can be thin, it is thicker than just plain disc, and now less discs fit in “tree”, so more floor space is needed (for discs that have much more information than discs with error correction).
But if information is for some streaming service, streaming film or music, if there is dropouts in video or audio that is not a tragedy, in DVD and Bluray discs are scratches and dirt that are played at home, and in CDs also scratches and dust, so video picture and CD sound have dropouts, but that is not much of a problem in video or audio, people are used to it, so if streamed video or audio has some dropouts it is no tragedy. If discs are in “Minigrip” bags and then in open air only few seconds during loading, and if some dust particles go to non-error corrected optical discs, and that leads to some dropouts in streamed picture or streamed sound, that is insignificant. In data centers. So no extreme “cleanroom” environment is needed in data center rooms that have optical discs for video or audio streaming. Home media needs either protective cartridges in optical discs if error correction is not used, or error correction is used and no cartridges.
Magneto-optical disc is one solution if Bluray/Archival disc optical discs are not used. LIMDOW and DWDD writing methods with magneto-optical discs, “Tunable magneto-optical effect” 2021 Yang et. al., “Magneto-optical characterization of melt-textured superconductors” 1999, “Detecting phase-resolved magnetization dynamics by magneto-optic effects” 2021, “Large magneto-optical effects and magnetic anisotropy energy” 2018, “Swiss researches develop first magnetic photoconductor” 2016, “A review of magneto-optical effect and its application” 2017, patent EP97930771A1 Magneto-optical recording medium 1991, "Investigating the vortex melting phenomenon using a novel differential magneto-optical imaging technique.
In laptop PCs ordinary small LTO cassette of 10 x 10 cm can be used, tape drive inside laptop PC, LTO has 18 terabytes uncompressed capacity. LTO cassette is one half size of VHS cassette with only one reel, because LTO cartridge actually really is one half of VHS cassette, its dimensions and other properties are almost identical to VHS cassette without takeup reel. VHS cassettes are really cheap. Somehow LTO cassette has been turned to super expensive system in data center use only, in a time when every home PC welcomes cheap data storage of 18 terabytes and more. I really don t understand that business model, making cheap technology like LTO cassette to super expensive when it can be used to distribute digital films with practically no video compression and large pixel rate, and used in myriad other tasks also in home PC ,or even in laptop PC.
If VHS cassette would have been made for only large TV broadcast stations, not at home use, it would have failed commercially, and optical disc mass memory and LTO is going to same way, nobody really is interested million dollar or 100 000 dollar systems when semiconductor memory is about same cost, making expensive from something really cheap just spoils competing advantage of some cheap product, and advantages in price are enormous when semiconductor memory and optical or tape memory are compared.
Sony sells Archival disc to data centers with up to 5 X 120 mm disc drives, of course with hefty price. That is insanity if Bluray disc can be bought blank writable ROM disc at few cent price in China. So Sony packed 5 of those 0,005 dollar discs or so and then sells that at 100 000 dollar price or so. It is insanity.
Everybody can build at home similar optical RAID station that Sony sells, just buy five Discman players from China, choose DVD option (not CD), and use DVD-ROM discs. Connect those five Discmans to your PC and there it is, practically same system that Sony sells for data centers at 100 000 dollar price or so. DVD-ROM discs have no capacity of Archival disc and discs can be read in one side only, but technology is the same that is in Archival disc, nothing much different. But your own personal “Archival disc system” cost only few dozen dollars, or less than 100 dollars. This is the way that optical disc memory system should be, not mega expensive system that uses discs that cost fraction of an dollar, but whole system is 100 000 dollar or so.

If optical discs are packed in a “tree” optical drive, which is just several optical drives stacked in vertical arrangement, and this stacked optical drive tree can have 77-80 discs in home PC system, each have individual electric motors and laser pickups (several per disc side is possible because laser pickups are cheap. Disc has two sides so at two sides of disc are laser pickups needed). Cost of cheap chinese Discman player can be used as comparison point what each of these disc units in a “tree” cost, and complete cost of system is the price of how many discs (how many individual Archival disc disc drives) are in “tree”. Office/workplace PC workstation can have more expensive 256 -260 disc system, from floor ground to top room ceiling so floor space is minimized but manhandling discs from floor level to room ceiling perhaps little difficult, from ground up to 3 m - 3,5 m high “tree” or “tower”. If discs are 380 mm diameter (15 inch) that is 10 times more than in 120 mm disc, so if Archival disc has four layers that is about 390 gigabytes. 38 cm disc is then 3,9 terabytes. Also smaller discs like 120 mm or 203 mm can be used in 380 mm disc drive, so in home use that disc drive tree can be used to play CDs, DVDs, Blurays and Ultra HD Blurays, and DVD-ROMs etc. It is possible that no error correction is used so discs are inside protective cartridge like earliest Bluray discs. And that plastic cartridge does not even cost much, in China is jewelcase CD cases sold at 0,005 dollar price or so, so then price is small for both disc and its protective cartridge, but now many laser pickups per side cannot be used and perhaps cartridge system is a bit awkward. However Dataplay discs showed that information density is high without error correction. “Tree” of disc drives is also higher if discs have cartridges surrounding them. About 256-260 discs of 38 cm without error correction is one petabyte. About 78-80 discs in home PC system is 300 terabytes.
Each disc needs to encoded/decoded with information. No separate electronics is needed for each disc, in disc “tree” is just one processor that handles all discs, either about 80 or 260 discs. That saves costs (probably). Bluray discs have been about 20 years. Semiconductor circuits have become much smaller since 20 years ago. So one integrated processor can handle all 80 or 260 discs. It can be some cheap available CPU or special ASIC made for this “tree” disc drive. No need for 80 or 260 individual chips for each optical drive in a tree. If it is cheaper that there is only one processor not many.
Electric motors can be outside disc center axle, they can use belt drive or chain drive to spin disc axle, or use straight metal axle that goes sideways to disc axle and spinning power turns there to 90 degrees, like car axles do. There is worm gear (worm drive) etc., possibilities. Another way is to use direct gearwheel connection from electric motor to disc axle, gearwheel must then be about 120 mm diameter like disc itself if electric motor is outside of the 120 mm disc, and this gearwheel makes disc drive bit large. But when electric motor that spins the disc is outside spinning axle of discs “tree” of disc drives can be shorter when discs are close each other and there is no electric motor and its gear in axle of the disc. So belt drive or chain drive, 90 degree turn axle or simply large gearwheel can be used to spin disc if the motor is outside of the disc diameter area, in 380 mm disc gearwheel must be 380 mm size so not suitable for those big discs, but belt drive or axle power possible etc.
Laptop PCs can even have both internal LTO tape drive that has 10 X 10 cm cassettes of 18 terabytes uncompressed capacity and small disc drive of 12 X 120 mm discs, only one motor, for simplicity and cheapness. 12 X 120 mm Archival discs are in a rigid “tree” frame, perhaps 60 mm to 70 mm thick, and this pack goes from hatch (top loading) bay of laptop PC, so it is like Discman player built in laptop PC, but it has deeper bay. Individual discs can be changed in a “tree” frame of 12 discs. Capacity is about 4,65 terabytes, 12 X 390 GB Archival discs, about 1000 times more than in DVD-ROM disc of one layer. Discs themselves cost almost nothing, so it is practically ultra-cheap 4,7 terabyte optical memory in laptop PC. And also 18 terabyte tape drive can be in same laptop perhaps.
Then large data center optical drives and magnetic tape drives. Why they must be so large, one petabyte big LTO cassette of 360 - 365 mm (14 inch) diameter and 2 inch (51 mm) tape, and 193 cm (76 inch) 100 terabyte optical disc? Because both optical disc and magnetic tape are cheap, it is the disc/tape drive that makes the cost. So large 193 cm optical disc needs only one electric motor and laser pickups system (there can be dozens of them in one disc side of 193 cm disc). Only one tape drive is needed for large petabyte LTO cassette, like only one is needed in small 18 terabyte 10 X 10 cm cassette. Maximizing economics of scale, making optical discs (absurdly) large and LTO cassettes too cost of whole system is minimized. And Exabyte data store is now super cheap, and compact, it needs very little floor space. Even Zettabyte data center is now possible, cost is hundreds of millions of dollars over 200 million if petabyte LTO drives are used, and over 500 million (perhaps) if 193 cm Archival discs are used. Both tape and optical disc use robotic loading system in data center. But it is still astronomically cheaper than semiconductor memory of same size.
In home use either 450 terabyte LTO tape or 38 cm optical disc can be used for Hollywood film distribution. Perhaps 450 terabytes is too much so tape length inside cassette is smaller, although now Hollywood films can have almost unlimited pixel count. 360 degree virtual worlds with retina display quality when looked through 3D glasses. Cost is small, magnetic tape is cheap. Also big screen IMAX films or normal silver screen films with retina display quality. Cinema theaters can use big petabyte LTO cassettes, several cassettes can be consumed in normal 1,5 hour to 2 hour film, two tape drives are used, other starts when another one stops, like film projectors in cinemas are two, when reel is changed other projector is working. So multi-petabyte Hollywood digital films are now possible to be shown in cinemas.
Films can be video compressed, no need to use uncompressed or not even lossless compressed. But perceptually / subjectively compressed video will do. If human eye cannot see difference between compressed and uncompressed video, makes no sense to use uncompressed video, compressed video is as good quality if humans cannot see the difference. But nowdays video compression is visible, it is possible to see video blocks (stiff / freezed background and then moving objects like people and cars in front of this stiff background) in big screen, and motion blur also. When video compression reaches level that video compression artifacts cannot be detected, that is perfect video coding. It is reported that success of 3D films have waned. Perhaps because in 3D people see video compression clearer than in 2D screen, so they dislike it. Making video compression invisible can bring 3D films back to success and every film can be shoot at 3D. When shooting digital film for example news groups can use portable cameras that store video in 450 terabyte portable video recorder, it is a small bag sized but it is portable. In Hollywood films petabyte cassette can be used when filming and using two or more tape drives “on the fly” so fast change from one cassette to another is not a problem and endless amount of cheap data store, many petabytes, is possible.
38 cm optical Archival disc can be used to distribute Hollywood films, capacity is 3,9 terabytes. Smaller than in 450 terabyte tape drive, if only one disc is used, but now fast search and skip options can be used like in DVD or Bluray. One 38 cm disc cost almost nothing, four 1 terabyte USB memory sticks is 100 dollar to 200 dollars, and content in that memory has cost too. Discs packed like vinyl LPs, they are now videodiscs, 38 cm size, in cardboard sleeves. They are thinner and lighter than vinyl LPs. Ecodisc optical disc manufacturing, if that is suitable, can be used.
Large petabyte LTO cassette can be used in analog sound recording, if tape is 2 inch wide 64 tracks or 48 tracks is possible, or 32 tracks if budged-priced analog tape recorder is used. Tape cassette is put to table like normal old 24 track tape recorder, tape pulled out and put to takeup reel like normal 24 track recorder, so now normal razorblade editing can be used with LTO cassette. Downmixed to 48 tracks or 32 tracks surround sound in 450 terabytes home PC LTO cassette that is now used to store multitrack analog surround sound for home theater. Two track stereo mix also included in that multitrack capacity. Analog sound tape use different tape surface formula than digital data tapes, but that analog audio tape can be packed inside LTO cassette, even to small 10 X 10 cm LTO cassette.

For large 193 cm 100 terabyte discs in data centers, it is even possible to use stamping process to make them if they have prerecorded content. Roll to roll manufacturing can be perhaps used to make blank optical or magneto-optical discs, but if already stored content is needed perhaps DVD / Bluray factory can be converted to use 193 cm diameter stamping of optical discs. Ecodisc manufacturing, cheaper and environmental friendly, no harmful chemicals used. Because stamping optical disc is same process if either 120 mm disc or 1930 mm disc is used, only disc is bigger, so price of making 193 cm discs like normal Bluray discs (with Ecodisc method) is perhaps not so expensive at all, mass manufacturing of large numbers of them for datacenters.
Floor space needed is smallest if petabyte tape drives are used and possibly cheaper than optical disc drives per information capacity. Million (if 1000 petabytes are used not 1024) petabyte LTO tape drives are needed in Zettabyte data store. if one petabyte tape drive cost is compared to VHS player, perhaps 200 dollar is suitable for petabyte tape drive of one cassette. So 200 million dollars without robotic loading system and building costs.
If tape drive is 0,75 m X 0,4 m X 0,15 m size, and they are stacked to 25 in vertical, 25 X 0,15 m is 3,75 m high. 1000 000 : 25 = 40 000. Then 0,75 X 0,4 m is 0,3 square m floor space. Then 40 000 X 0,3 square m is 12 000 square m floor space needed for tape drives if they are 25 stacked vertically. Robotic loading system needs 0,4 m and two tape drive walls are back to back, robotic loader can load to left and right, 0,4 X 0,4 m is 0,16 square meters, which is needed space per each tower of 25 LTO tape drives that robotic loader needs, then 40 000 X 0,16 = 6400 square m, that divided by two (robotic loader can load both left and right) is 3200 square m. 12 000 + 3200 = 15 200 square m. Zettabyte data store fits in a building that is 125 X 122 m sized, in one floor. That is ridiculous low amount of floorspace for Zettabyte data store. If I counted everything right. And then also “cold storage” space is needed where robotic loading system takes LTO cassettes and loads them to tape drives and takes back to storage. So now Zettabyte data store is many-Zettabyte data store. But magnetic tape is cheap. And only one Zettabyte can be used at same time in tape drives, others are in “cold store” waiting to be loaded.
But basically whole internet information of the world, from every country, whole internet with its cloud services, can be in one quite small data center, only lots of petabyte LTO cassettes are needed, perhaps about 25 LTO cassettes per available tape drive in Zettabyte data room, and now one quite small data center can have all internet of the world, which represents about 60% of all data in the world, rest 40% is in home PCs or other places outside internet and its cloud services. And in cheap price too, in that data room and its cold store LTO cassettes stored outside of that Zettabyte data room.

Optical store will be larger, if 333 of 193 cm disc (100 terabyte each) drives are stacked in a “tree”, that is perhaps 4 m high. Disc drive is 2 x 2 m about. 333 X 0,1 petabyte is 33,3 petabytes. Zettabyte is 1000 000 petabytes (1000 not 1024 is used for counting binary data in this case), 1000 000 : 33,3 = 30 000 square meters. Robotic loader needs 2x 2 m too, disc drive tree walls are back to back, loader loads left and right, 30 000 : 2 = 15 000 square meters, 45 000 square meters together. That is building of 215 X 210 m size, in one floor. Still very little floor space for Zettabyte data store. If I counted right. And optical discs are much faster than tape drives, and cheaper too. But if one 193 cm optical drive costs only 50 dollars, cost of 10 million of them in that data center is 500 million dollars, plus robotic loading system and building cost. Also cold store is needed for extra optical discs, Zettabyte is only capacity that is used all time in 10 million optical drives in data room. Many Zettabytes can be in extra discs that are not in optical drives at that moment. Costs of optical discs and petabyte LTO cassettes must also be counted if cost of Zettabyte data store is counted, but price is relatively low of optical discs and magnetic tape when mass produced in large quantities.
But for example ordinary small 10 x 10 cm LTO cassette can store 580 terabytes in future generation of LTO tape, in 1255 m long tape that is thinner than 1065 m long 18 terabyte LTO tape. Also already in 2013 almost 10 years ago 1000 terabytes (one petabyte) was put to 120 mm DVD disc in experimental optical system.
If multilevel recording is used, so that intensity of laser pits varies, lots of more information can be stored. If two lasers with two different frequency are used, two color coordinate system can be used, and now color can be used to store information, not only black and white pits, and information space comes larger again. Multilevel recording of intensity of pits and color recording of two or three lasers that form two-color or three-color coordinate system can perhaps be combined so information space expands once more. Length of the pits can be also varied, like in Laserdisc, and then length of pits, intensity of them, and colors can be used together, information space is larger again. If analog data recording is used, without quantization steps, in color and pit length and intensity multilevel recording, data space then becomes even larger again.
If Zettabyte optical data center needs 45 000 square meters, then if this store is in 15 floor high building, each floor needs 3000 square meters, which is 50 m X 60 M. Now room is small enough so that when “cold storage” of optical discs are placed just outside of this room, robotic loading system can perhaps only in few seconds find and load optical discs from cold storage and put them to disc drives. Zettabyte means that those are discs that always are in optical drives, those that are in cold storage are extra discs, so this data center can have several Zettabytes or several dozen Zettabytes capacity, because optical discs themselves are cheap, it is the cost of optical disc drives that makes the cost.
LTO tapes are slow, because they are designed to be archive data store where speed is not important. So they must be much higher speed than nowdays if they are used for something else than just data archive duties in big data centers. If LTO tapes are used to store things like high quality digital film, that is linear information so LTO tape drive can be used faster than when information is divided to be in several places in LTO tape. Future 580 terabyte LTO tape has read/write speed of 1,9 terabytes / second? So less than 10 minutes is one petabyte LTO tape fully written / read? Next generation LTO from 18 terabytes upwards (LTO 10) is designed for 1,1 gigabytes / second, which still sounds bit slow, then in digital picture video compression must be used, or if tape is wider than 12,7 mm 1/2 inch, does wide tape read/write faster? If LTO tape is used in filming digital movie then several LTO tape drives must be used together so that data speed is fast enough, or use several optical disc drives like in a “tree” arrangement so that data speed is fast. But optical discs themselves and magnetic tape is cheap.
TOMdisc is one of several firms that past 15 years have promised terabyte optical disc in 120 mm. Folio Photonics in 2019 did the same. None of those terabyte- class 120 mm discs have materialized, at least not yet. “Sub-terabyte optical disc realized with three-dimensional pit selection”, “Multilayer 500 Gbyte optical disk”, “Large format multifunction 2-terabyte optical disk storage”, “Toward terabyte two-photon 3D disk”, “Real-time storage and retrieval of SAR imagery using optical disc jukebox” 1992.

If there is optical disc mass memory that use large discs, 8 inch (203 mm), 15 inch (380 mm) or even 76 inch (1930 mm), that is not so strange, 1980s / 1990s were 12 inch and 14 inch magneto-optical discs platters used in data centers. Optical or magneto-optical discs are also cheapest form of mass memory.
Their information density can be increased if error correction is not used. Old Dataplay discs were small but they had high information density, during that time.
Instead of error correction discs can be enclosed in protective cartridges like earliest Bluray discs, and that cartridge does not even rise the cost of disc (with cartridge) much, price of for example CD jewelcases are about the same as CD discs, when bought from China, so cost of both CD and its plastic case is ultra cheap when bought in large amounts from factory.
But is it possible not to use error correction and not to use protective cartridge? If there is cleaning method in the disc drive that clears dust particles in front of laser pickup.
For example in laser pickup is miniature air nozzle that blows air to optical disc about 45 degree angle forward, so that dust particles fly away from laser pickup, and then is miniature brush in laser pickup that clears path for laser rays just before laser. This brush is microscopic size wide, because the pits that laser reads are microscopic size too. So there is physical contact with the disc in laser pickup but that is very gentle and small-area.
Also is thing called “Milty Zerostat” used for making Vinyl LPs antistatic. In optical disc drive can be inbuild zerostat- type device that when disc is loaded in disc drive disc will have zerostat treatment, that makes disc antistatic and lets dust particles loose so that air blower in laser pickup can blow dust away. In disc drive also can be larger air blower that in the moment when disc is loaded to disc drive and has got zerostat treatment, also blows air and blows loose dust particles away from disc drive. If optical discs are enclosed in “Minigrip bags” that are antistatic when discs are outside disc drive and they are taken from Minigrip bags when loaded to disc drive and when taken away from them, discs are only few seconds exposed to open air. In robotic loading systems of data centers can be similar washing/cleaning machines that are sold for vinyl LPs for cleaning vinyl LPs. In data centers those automatic washing/cleaning machines clean optical discs and enclose them to “Minigrip bags”. Process happens automatically, when robotic loading system takes away disc from disc drive and loads another disc to it, old disc from disc drive is robotically put to Minigrip bag, and taken to washing machine where possible dust particles that disc may have when exposed to open air few seconds are taken away, and then put to MInigrip bag again and taken to “cold storage” where is thousands or millions of optical discs when they are not in the disc drives.
Also “cleanroom” environment can be in automatic robotic data center, but not so absolute clean that semiconductor factories have, smaller amount of sterility is enough in data center which uses optical discs without error correction? If disc cleaning systems are used?
Perhaps is possible that protective cartridge which is included with each optical disc is not needed, only cleaning methods in data center and discs put to hermetically enclosed “Minigrip bags”. In home PC optical disc systems also perhaps only disc cleaning methods are enough, zerostat, air blower, and brush in laser pickup, and discs are manually loaded and offloaded from “Minigrip bags”. But protective plastic cartridge does not make disc price much more, actually cartridge makes optical disc price double, if cartridge has about same cost as disc itself, but both cartridge and disc itself are so cheap that price per disc is neglible. But cartridge perhaps makes optical disc system bit awkward.
Also many laser pickups can be used to read one disc side, and they each can have own air bowing miniature (almost microscopic) air blowing nozzle and miniature microscopic brush.
But optical discs are cheap, so error correction can be used, and is used in Archival discs and Bluray discs (Archival disc is version of Bluray disc).