For the purpose of this module removable media includes external
devices such as CD-ROM, tape, and floppy drives. These are
also referred to as storage devices as they are used to hold program data
and other information.
Each vendor provides documentation regarding which removable media devices
are known to work with its system. This generally means that the
appropriate device drivers are a standard part of the operating system.
Other peripherals may work with a given system, but the device drivers
will have to be added. Additionally an unsupported device may not be
compatible with other utilities on the system.
Selecting a CD-ROM or floppy drive is a fairly straightforward
process. There are, however, a variety of tape drives available for
different tape formats and capacities.
- Quarter Inch Cartridge. This acronym is also reported to stand for
Quarter Inch Committee. There are standards for QIC drives so that drives
produced by different companies are interchangeable. Additionally
hardware and software development standards for QIC subsystems allows
a quarter-inch data cartridge recorded on one system to be used with
another compatible system. These drives are made to work with differing
lengths and can copy at different densities. The last three digits of
the model number refer to the drive capacity in MB. The most
common cartridge tapes are QIC-150, QIC-320, and QIC-525. Usually
QIC drives can read tapes written in a less dense format, although
they may not be able to write to them. QIC drives cannot
- 4mm DAT (Digital Audio Tape)
- The DAT standard for data storage is DDS (Digital Data Storage).
However, the drive and the media are similar to audio DAT. DAT tapes
are about the size of a match box and are the smallest magnetic
media available. Each tape holds around 2 GB of data. This can be
increased up to 8 GB with compression.
- 8mm DAT (Digital Audio Tape)
- These drives are sometimes referred to as "Exabytes" as they were
the first company that made them. They record to standard 8mm videotapes.
Original format holds 2 GB of data while the newer format will hold
5 GB. Compression on some drives can push the capacity up to 10 GB.
8mm tape drives contain drive mechanisms that are know for drifting
out of alignment every few years.
- DLT (Digital Linear Tape)
- These drives have a storage capacity of up to 40 GB per tape
with compression. DLT drives are designed with a dual-channel
read/write head which allows them to record data twice as fast
as other drives at a given speed and recording density.
An additional note on floppy drives and disks:
there are utilities
available that allow Unix to read DOS or Mac floppies.
Mtools is set of public domain programs that
enables Unix to manipulate MS-DOS files. SGIs will read both DOS and Mac
floppies. Under IRIX, the mediad daemon
determines the format of the floppy disk and if it is Mac or DOS,
mounts the filesystem on the default mount directory. From this
directory regular Unix commands can be used to access the files.
Adding removable media to a system involves three basic steps:
The specific details vary from system to system.
- Powering down the system.
- Installing the device. This includes connecting it physically,
setting the SCSI ID, and making sure the proper device drivers are
- Powering the system back up.
Up to six SCSI devices may be daisy chained together. This means
that rather than attaching peripherals to the computer itself they
may be hooked up to each other. The last device in the chain must
be terminated with an active terminator. This terminator should
come with the device.
Each SCSI device must have a unique SCSI ID or address. This
is a number between 0 and 7. One of these IDs is reserved for the
controller, either 0 or 7. To find out which SCSI addresses are
Unfortunately there is no single solution for getting this information
under Linux. The command dmesg may work. If Linux is
running with a fairly new kernel, cat /proc/scsi/scsi
may work. There is also a file in the /proc/scsi directory for
the SCSI host adapter that the system is using. Depending on which
driver is in use, this file may also contain the relevant information.
The SCSI ID can be set with a switch, dial, or jumper as per the
instructions that come with the device. The device should also come with
instructions on how to physically attach it to a system, including
which cables are needed, etc.
For details on the installation process for each
platform please see:
QIC, DAT, compression, DLT,