Subject: Re: ISO image of NetBSD 2.0_BETA/mac68k (2004-06-12)
To: 'port-mac68k@netbsd.org' <port-mac68k@netbsd.org>
From: Schwerzmann, Stephan <stephan.schwerzmann@schmid-telecom.ch>
List: port-mac68k
Date: 06/23/2004 17:54:53
>>No? I did a little experimenting, and found that the old Apple 300i
>>can read Memorex 48X CD-R media (burned at 24X for good measure), but
>>not TDK CD-RW.
>
>From my experience, drives older than about 1998 apparently are not able to
>read CD-RW. I've seen this with
>
>- the cdrom drive in a Quadra 650
>- the cdrom drive of a Thinkpad 380D (~1997)
>- a Philips 8x SCSI drive (~1998) with Windows 95.
>

  for my understanding of the matter, it must be so.

  the parameters of the optical systems CD-ROM <-> CD-R <-> CD-RW
are different: for one, on a genuine CD-ROM the pits and lands are
at real different heights (think old mechanical music box for what 
concerns the media), resulting in different lengths of the path 
the light beam has to trace for a '1' to a '0', resulting in  
beam/no-beam at the detector (*)
	<http://entertainment.howstuffworks.com/cd1.htm>
	<http://entertainment.howstuffworks.com/cd5.htm> <- nice!

(* whether phase shift and thus beam annihilation or 
deflection to another spot off the detector I don't know)

  then on CD-R and CD-RW the pits and lands are no more made
with difference heights but different light beam reflection
caracteristics (think black & white), resulting in something more
similar to CW (Carriwe Wave Modulation for morse communication,
no OM round here?) aka beam/no-beam at the detector
	<http://computer.howstuffworks.com/question287.htm>

  finally on CD-RW, much similar to CD-R, the difference between
lands and pits is just weaker (think light gray & dark gray)
calling for more sensitive detectors
	<http://electronics.howstuffworks.com/question655.htm>

  the CD-R system is conceived to be CD-ROM compatible
=> high chance that CD-R media works in vintage CD-ROM drives

  OTOH CD-RW is conceived to be feasible at all, at the price
that drives must be "CD-RW"-ready to be able to read such media
(modern 'read-only' drives are - meaning they probe the media
and then switch the 'pickup' into appropriate operation mode)

  since the 3 system technologies were developed at different 
times, how can you pretend a vintage drive 'is aware' of later
technology?

Stephan

NB: from here go <http://www.pctechguide.com/09cdr-rw.htm>