Zip Drive

The Zip drive is a medium-capacity removable disk storage system, introduced by Iomega in late 1994. Originally it had a capacity of 100 MB, but later versions increased this to first 250 MB and then 750 MB.
The format became the most popular of the super-floppy type products but never reached the status of a quasi-standard to replace the 3.5-inch floppy disk. It has been superseded by flash-drive systems as well as rewritable CDs and DVDs, and is fading in popularity. The Zip brand was also used for an external CD writer known as the Zip-CD.

Design

The Zip system is based loosely on Iomega's earlier Bernoulli Box system; in both systems, a set of read/write heads mounted on a linear actuator flies over a rapidly spinning floppy disk mounted in a sturdy cartridge. The Zip disk uses smaller media (about the size of a 9 cm (3.5") microfloppy, rather than the compact disc-sized Bernoulli media), and a simplified drive design that reduced its overall cost. This resulted in a disk that has all of the 9 cm (3.5") floppy's convenience, but holds much more data, with performance that is much quicker than a standard floppy drive (though not directly competitive with hard drives). The original Zip drive had a data transfer rate of about 1 megabyte/second and a seek time of 28 milliseconds on average, compared to a standard 1.44 MB floppy's 500 kbit/s (62.5 kB/s) transfer rate and several-hundred millisecond average seek time (today's average 7200 RPM desktop hard drives have average seek times of around 8.5-9 ms).

Interfaces

Zip drives have been made with a variety of interfaces to the computer. Internal drives have been made with both IDE and SCSI interfaces. External drives with parallel and SCSI interfaces and (some years later) USB. For a while, there was a drive called the Zip Plus which was supposed to be able to autodetect between parallel and SCSI, but there were lots of compatibility problems reported and the drive was later dropped. The Zip Plus drive included additional software and a smaller power adapter than the original Zip drives.

Capacity

The initial Zip system was introduced with a capacity of 100 megabytes. Plans were considered for a lower cost 25 MB version that would work in the same 100 MB drive — the idea being to bring the price of a Zip disk closer to that of an ordinary floppy — but these disks seem not to have been released. The introduction of the 100 megabyte disk quickly made Zip a success and people used them to store files larger than the 1.44 MB capacity of regular floppy disks. As time went on, Iomega eventually increased the capacity to 250 and later 750 megabytes, while improving the data transfer rate and seek times.

Media

Zip media is thicker, but otherwise similar in size to 3.5" (9 cm) floppy disks, which means the drive slot is large enough to accept such a floppy. To prevent drive and disk damage, the underside of Zip media cases include a retroreflective spot in one corner. The drive mechanism will not engage if the reflective spot is not detected.

Compatibility

Higher capacity Zip disks must be used in a drive with at least the same capacity ability. Generally, higher capacity drives also handle all lower capacity media, although the 250 MB drive is much slower than the 100 MB one to write data on a 100 MB disk. The 750 MB drive, however, cannot write to the 100 MB media, which is the cheapest and most common. The retroreflective spot differs on the three media sizes such that if a larger disk is inserted in a smaller capacity drive, the disk is immediately ejected again without any attempt being made to access the disk.

Features and implementation

Unlike other diskette formats, the Zip's write protection is implemented both in software and in hardware instead of just in the disk controller itself. The metadata on the disk indicates the write protection status, which the drive then enforces to the host computer. To change protection settings, the computer issues commands to the drive to change the metadata on the Zip disk. This means that the disk must be loaded in a drive and accessed on a computer with the appropriate software to turn write protection on or off. It also means that, in theory, a rogue driver or a modified Zip drive could be created which ignores the write protection flag. The Zip system also introduced media access protection via a password. Like write protection, this is also implemented on the software level. When a disk is inserted, the Zip drive reads the metadata; if the data indicates the disk should be read-locked, the drive awaits a password from the computer. Until it receives such a password, the drive pretends to still be empty (to basic disk I/O commands). Once the password has been sent and verified, the drive "activates" the disk in the drive and allows access. One side effect of this implementation is that, on some drive models, it is possible to trick the software into allowing access to a different disk than it believes to be in the drive, thereby bypassing the password protection. The protection does not use any encryption; it simply is a combination of metadata on the disk and cooperation from the Zip drive's firmware.

The ZipCD Drive

Iomega also produced a line of internal and external recordable CD drives under the Zip brand in the late 1990s, called the ZipCD 650. It used regular CD-R media and had no format relation to the magnetic Zip drive. The external models were installed in a Zip drive-style case, and utilised standard USB 1.1 connections. Iomega used the DirectCD software from Adaptec to allow UDF drive-letter access to CD-R or CD-RW media. The company also released their own CD-R and CD-RW media under the same ZipCD name. However, the ZipCD drives would burn to any blank CD-R or CD-RW media.