Re: Which CD-ROM?

[dempson@atlantis.actrix.gen.nz (David Empson)]

In article <787000000.5993@myrias.ab.ca>, Devin Reade <gdr@myrias.ab.ca> wrote:
> In article <3c3ram$geq@werple.apana.org.au> davoesq@werple.apana.org.au (Stephen Davidson) writes:
> 
> >A CDROM150 id single speed, single session PhotoCD compatible drive
> >while the CDROM300 is double speed multi session PhotoCD compatible
> >and multispeed.
> 
> Here's another question for the FAQ, although I would appreciate an
> answer in someone's followup post:
> 
> So what is the significance of the following terms (in the context
> of CD ROM drives), and why would I want one feature vs another?
> 
> 	single speed   vs double (multi?) speed

This one is easy - the speed of the CD-ROM drive.  The big question
(which I've never known the answer to) is whether it refers to the
data transfer speed, the seek speed, or both.

To double the data transfer speed, the CD-ROM would need to spin twice
as fast.

I have also heard of triple speed and quadruple speed drives.

> 	single spin    vs double (multi?) spin

I don't know what this means.

> 	single session vs double (multi?) session

This only applies when using writeable CD-ROMs, i.e. CD-R (recordable)
disks.  With a CD-R disk, you can either write everything you want to
put on the disk in one session, or you can write some information,
then add/replace some of it later by writing to the unused portion of
the disk (any old information that was replaced is still there, but can
not be accessed any more).

The actual writing of the CD-R disk requires a special drive and
software, which are rather expensive.  I doubt there is any CD-R
writing software for the Apple II.

A CD-R disk can be read in a standard CD-ROM drive.

A "single session" CD-ROM drive can only read the data that was
written in the first writing session.  Any data added later cannot be
accessed.

A "multi session" CD-ROM drive can read all of the data written in all
writing sessions (though data that has been replaced may be
inaccessible).


The basic principle behind a multi-session CD is that a new directory
gets written for each session.  A multi-session CD-ROM drive looks for
the latest directory.  A single-session CD-ROM drive only looks for
the first directory.
-- 
David Empson
dempson@actrix.gen.nz
Snail mail: P.O. Box 27-103, Wellington, New Zealand