Numerous removable magnetic disk formats are available. Unfortunately, many are proprietary designs, so you may find yourself in a technological dead-end. In addition, magnetic disks are gradually being pushed out of the market, particularly with the increased capacity of solid-state storage devices and the falling cost of CD and DVD-based drives.
The following types of magnetic disk are commonly used:-
This 100 MB 31⁄2-inch disk is based on high-density floppy disk or super floppy technology, giving a respectable average seek time of 29 milliseconds (ms). At one time, the format was so popular that such drives were built into Apple computers. Early models had mechanical problems, a common failing in non-Winchester drives, but are now reasonably reliable.
This 250 MB version of the Zip 100 drive, which is also compatible with the original 100 MB disks, is 40% faster than the older version, although it’s actually slower when used with a 100 MB disk. The seek time is once again 29 ms, although the new drives provide an increased data transfer rate of up to 1.4 MB/s and have a 32 KB buffer built-in.
Yet another variation of the original Zip 100 drive, this time holding 750 MB and offering a transfer rate of up to 8 MB/s. These drives can read 100 and 250 MB disks and write to 250 MB disks, but can’t write to 100 MB disks.
This 120 MB 31⁄2-inch format is popular with PC users. Such drives also accept DS and HD floppy disks (but not the older SS variety), making them ideal for anyone who regularly works with diskettes.
The original version of this 4-inch format provides 1 GB of storage, employing a cartridge that contains two platters. The Jaz 2 format has an increased capacity of 2 GB, although the newer drives also accept the older 1 GB cartridges. Jaz disks are ideal for large graphics files, giving an average seek time of 12 ms and a transfer rate of up to 8.7 MB/s.
This 31⁄2-inch format, available in 400, 720, 800 and 1440 KB sizes, is used older Macs and PCs., although some sizes don’t work in some drives or in some versions of the Mac OS. The limited capacity of this format has made it almost obsolete.
Most of the following formats are either on the way out or are in the process being introduced:-
This hard disk format provides a very useful 2.2 GB of storage space with a transfer rate of up to 12.2 MB/s. The mechanism uses a single platter for improved reliability.
DCT, which is currently at the prototype stage. is a credit card-sized format that accommodates 1.5 GB on a 50 mm diameter disk. This is housed in a steel cartridge, the whole thing weighing only 9 grammes.
Most cartridges consist of a simple box containing a disk. However, the Peerless cartridge, based on IBM’s Travelstar technology, is sealed and also contains the heads. Each cartridge, accommodating 10 or 20 GB, is the size of a personal organiser and plugs into a matching base station.
This 40 MB format is small, making it useful for hand-held computers and electronic cameras.
A miniature 730 MB 50 mm format pioneered by Olympus, Sanyo, Hitachi and Maxell. Although primarily designed for use with cameras this format can also be used in other devices.
Several proprietary formats have come and gone over the years, so anyone who buys pioneering products should take note. The 10 MB floppy disk once produced by Verbatim has disappeared without trace, whilst the original Bernoulli (Iomega) 44 MB and Ricoh 50 MB cartridges were displaced by SyQuest products, which in turn have been replaced by Iomega devices.
This type of 51⁄4-inch floppy disk, as used in older PCs, comes in 160 KB, 180 KB, 320 KB, 360 KB and 1.2 MB sizes, but has been entirely superseded by the 31⁄2-inch diskette and other modern formats.
Also known as a Bernoulli disk, this format uses well-proven Winchester technology. The bulky 51⁄4-inch cartridges are available in 44 (45) MB, 88 (90) MB and 200 MB versions.
This is SyQuest’s first convenient 31⁄2-inch format, providing 105 MB of storage, later expanded to 270 MB but with backwards compatibility. Other makers have also produced drives with capacities of 540 MB or 750 MB, most of which can also read data from the smaller capacity cartridges.
A low-cost 31⁄2-inch format that arrived with the EZDrive EZ135, providing a capacity of 135 MB. The later EZFlyer drive accommodates similar 230 MB cartridges, although it also accepts the original 135 MB disks. Both formats are incompatible with the earlier 31⁄2-inch formats described above.
A 1 GB format, also available in a drive with USB connections.
A later SyQuest format that never really became established. It has a capacity of 1.5 GB, an average seek time of 10 ms and a transfer rate of up to 3.7 MB/s.
©Ray White 2004.