1 Zip Drive Basics

Zip® disks are high capacity, removable, magnetic disks, which can be read or written by ZIP drives from IOMEGA corporation. ZIP disks are similar to floppy disks, except that they are much faster, and have a much greater capacity. While floppy disks typically hold 1.44 megabytes, ZIP disks are available in two sizes, namely 100 megabytes and 250 megabytes. ZIP drives should not be confused with the super-floppy, a 120 megabyte floppy drive which also handles traditional 1.44 megabyte floppies.

IOMEGA also sells a higher capacity, higher performance drive called the Jaz®/JAZZ drive. Jaz drives come in 1 gigabyte and 2 gigabyte sizes.

ZIP drives are available as internal or external units, using one of three interfaces:

1. The SCSI (Small Computer Standard Interface) interface is the fastest, most sophisticated, most expandable, and most expensive interface. The SCSI interface is used by all types of computers from PC's to RISC workstations to minicomputers, to connect all types of peripherals such as disk drives, tape drives, scanners, and so on. SCSI ZIP drives may be internal or external, assuming your host adapter has an external connector.

   Note: If you are using an external SCSI device, it is important never to connect or disconnect it from the SCSI bus while the computer is running. Doing so may cause file-system damage on the disks that remain connected.

   If you want maximum performance and easy setup, the SCSI interface is the best choice. This will probably require adding a SCSI host adapter, since most PC's (except for high-performance servers) do not have built-in SCSI support. Each SCSI host adapter can support either 7 or 15 SCSI devices, depending on the model.

   Each SCSI device has its own controller, and these controllers are fairly intelligent and well standardized, (the second `S' in SCSI is for Standard) so from the operating system's point of view, all SCSI disk drives look about the same, as do all SCSI tape drives, etc. To support SCSI devices, the operating system need only have a driver for the particular host adapter, and a generic driver for each type of device, i.e. a SCSI disk driver, SCSI tape driver, and so on. There are some SCSI devices that can be better utilized with specialized drivers (e.g. DAT tape drives), but they tend to work OK with the generic driver, too. It is just that the generic drivers may not support some of the special features.

   Using a SCSI zip drive is simply a matter of determining which device file in the /dev directory represents the ZIP drive. This can be determined by looking at the boot messages while FreeBSD is booting (or in /var/log/messages after booting), where you will see a line something like this:

   da1: <IOMEGA ZIP 100 D.13> Removable Direct Access SCSI-2 Device
   

   This means that the ZIP drive is represented by the file /dev/da1.

2. The IDE (Integrated Drive Electronics) interface is a low-cost disk drive interface used by many desktop PC's. Most IDE devices are strictly internal.

   Performance of IDE ZIP drives is comparable to SCSI ZIP drives. (The IDE interface is not as fast as SCSI, but ZIP drives performance is limited mainly by the mechanics of the drive, not by the bus interface.)

   The drawback of the IDE interface is the limitations it imposes. Most IDE adapters can only support 2 devices, and IDE interfaces are not typically designed for the long term. For example, the original IDE interface would not support hard disks with more than 1024 cylinders, which forced a lot of people to upgrade their hardware prematurely. If you have plans to expand your PC by adding another disk, a tape drive, or scanner, you may want to invest in a SCSI host adapter and a SCSI ZIP drive to avoid problems in the future.

   IDE devices in FreeBSD are prefixed with an a. For example, an IDE hard disk might be /dev/ad0, an IDE (ATAPI) CDROM might be /dev/acd1, and so on.

3. The parallel port interface is popular for portable external devices such as external ZIP drives and scanners, because virtually every computer has a standard parallel port (usually used for printers). This makes things easy for people to transfer data between multiple computers by toting around their ZIP drive.

   Performance will generally be slower than a SCSI or IDE ZIP drive, since it is limited by the speed of the parallel port. Parallel port speed varies considerably between various computers, and can often be configured in the system BIOS. Some machines will also require BIOS configuration to operate the parallel port in bidirectional mode. (Parallel ports were originally designed only for output to printers)