CDROMS

Q. What is a CDROM drive?

A. A CDROM drive is a device which allows a computer to read
data stored on a Compact Disk. The CD is placed on a tray
(or sometimes in a caddy), and the contents of the disk read
by computer as with any other disk drive.

The disks themselves may contain nothing but audio
information (in which case they are normal "music" CDs) or
both audio and computer data or only computer data (in which
case they are CDROMS). The drives are made in standard 5.25
inch sizes, which fit into the drive bays of PC cases. For
Amiga users, the drives are usually housed in external boxes
which include power supplies.


Q. How does it work?

A. The CDROM is a plastic disk, coated with a reflective
surface on one side. Data is stored on the disk by making
little "pits" in the surface of the disk which are detected
by a low-power infra-red laser in the player. Each disk can
hold about 800Mb of data, or less if some space is reserved
for audio tracks. If the disk is a combined audio/CDROM, then
track one contains the computer data and subsequent tracks
contain the audio information.


Q. How can the Amiga deal with Audio CDs?

A. Usually the amount of control the Amiga has over an audio
CD is limited to the ability of playing, pausing and
skipping tracks. The audio output is available from the
front panel of the CDROM drive (most drives have headphone
sockets) or at the rear on a miniature connector.

Some CDROM drives support a feature called "CDDA". This
allows the audio data to be transmitted over the data bus
and into the Amiga. From here it can be converted into audio
data and replayed through the Amiga audio outputs. It's also
possible to store the data on disk: effectively working as a
high quality sampler.


Q. Can you write to a CDROM?

A. You cannot store data on a standard CDROM with a standard
CDROM drive. They are "Read Only" which is where the name
"Compact Disk Read Only Memory" comes from. However, there
is software available which gives the impression of writing
to the disk by storing the changes on a hard disk. When data
is read from the CD, any new material is actually read from
the hard disk and not the CDROM. 

If you want to create your own CDROMs, you'll need a special
CDROM Burner, which costs at least £500 and up, and special
write-able blank CDROMs. You'll also need special software,
such as MasterISO from Blittersoft, and an Amiga with a very
fast SCSI interface. The art of DIY CDROMs is still in its
infancy, and devices such as the Iomega Jazz can usually do
the job better and faster for the small-scale distribution
of data.


Q. Should I consider getting a CDROM drive?

A. Definitely. CDROMs store an amazing amount of data, and
if you like shareware or public domain you'll be in seventh
heaven. Buy a few Aminet disks for example, and you'll have
enough gigabytes of software to keep you busy for weeks.
Buying software on CDROM is also a lot cheaper than
downloading it all from BBSs or the Internet. DTP fans will
love the amount of fonts and clip art available. Anyone with
an interest in graphics will also appreciate the many disks
available, packed with images.


Q. What types of CDROM drive are there?

A. There are two main types: SCSI and a form of IDE. Other
standards exist from the PC world, where it was common
practice to connect the CDROM drive to an internal sound
card. This lead to several proprietry interface standards.
These days SCSI and IDE are the clear leaders. Most PCs have
IDE hard drives, and the IDE CDROM drive simply attaches to
the same cable.


Q. Which should I use on my Amiga?

A. It's up to you. The A600, A1200 and A4000 computers have
an IDE hard drive interface built-in, and Blittersoft are
selling a cable and software package which allows IDE CDROM
drives to be used. It's also possible to get a device which
houses a harddrive and CDROM drive in an external tower
case, such as the Intrinsic Tower. Alternatively, any Amiga
SCSI interface (e.g. Squirrel, Surf Squirrel or one which is
part of an accelerator card) can be used with a SCSI CDROM
drive.


Q. How do I connect one to my Amiga?

A. That depends on which Amiga you have. if you have an
A1200, the easiest way is probably to buy an all-in-one pack
which includes a SCSI interface and a CDROM drive and power
supply already housed in a single box. This will cost about
£180. Amiga Technologies demonstrated a drive which
connected directly to the PCMCIA port of the A1200 for £240.


Q. What speed of drive should I get?

A. CDROM drives are getting faster and faster -- eight speed
models (that is, drives which are eight times faster than
standard audio CDs) are the latest thing. That said, a
double speed one will do fine for 99% of the time, and also
save you quite a lot of money into the bargain.


Q. Can I use PC CDROM titles?

A. The Amiga can read the information on the CDROMs, but you
cannot run the programs. For example, a CDROM sold for PCs
containing GIF graphics files is perfectably useable by the
Amiga. However, a game for the PC released on CDROM cannot
be used. Yes, you can get just about run DOS software with
an emulator (PC Task includes CDROM driving software) but
the emulator runs so slowly you would not be able to play
games for example.