We had the 5ľ inch floppy disks then we had the 3Ĺ inch floppy disks. In both cases the media will only last a few years. The magnetic coating begins to flake off the Mylar disk taking the data with it. Within a decade or so the media is unreadable even with ďproperĒ care. Not to mention the small amount of data that they actually held, just 1.2 and 1.44 MB respectively.
And those two formats are not available today. In just a few years time, (remember we are talking about long term here) the industry has changed. You canít buy floppy disks in a store anymore and even if you had one can you find a computer that has a floppy disk drive in it?
Magnetic tape is even more outdated than floppy drives. Even back when it was the only choice it was a poor choice. Just finding the data somewhere along that long strip of tape made them very slow. And the magnetic material would flake off and accumulate on the tape heads, of course taking the data with it. Backup tapes often had to be replaced two or three times a year. Suffice it to say, I have never been a fan of tape systems.
OK I am going way back now. In the computer world that ended thirty years ago, although some election officials didnít seem to get the message until much later. The little holes punched in the cardboard were supposed to represent data bits but just get one card in the stack out of order and the system fails. Slow and error prone data storage meant that computers were just not reliable devices back in those days.
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CDís, DVDís and Blu-Ray disks are much more durable that floppy disks. Eventually the polycarbonate plastic will degrade and become milky white rendering the disk unreadable. But if you keep them out of sunlight they may last for millennia. That helps with the first basic question of how long will the media last. The second question is more problematic. CDís have largely been replaced by DVDís and Blu-Ray is beginning to replace DVDís. A thousand years from now the CD itself may still be good but will there be any CD players around?
Another feature of optical disks is that once the data is recorded it is permanently burned to the disk. Once the laser burns the little dots or dashes into the media there is no way to un-burn them. Even the rewriteable disks still have the original data encoded. They just keep moving to the unused part of the disk. Eventually the disk fills up anyway. The exception to this is the phase change storage used in some of the new rewritable Blu-Ray disks. Those can be erased and rewritten.
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Flash memory was developed by Toshiba back in the early nineteen eighties. There are two basic types, NAND and NOR named for the type of logic gates they are based on.
The NOR type is more commonly used in Computer BIOS, Set-top boxes and automotive computers where the program seldom changes. It has long write/erase times but allows random access to any memory location but the endurance may be as little as 100 erase cycles.
NAND type is more commonly used in USB, flash drive and solid state drive devices. It is faster and requires less chip area per cell. But it does not allow random access, data must be read on a block-wise basis and the block size may be thousands of bits. NAND type also has much greater endurance with over a million erase cycles.