4 Jul
2004
4 Jul
'04
5:39 p.m.
Jules Richardson wrote:
Silly question, I know...
I need to create a CD with files on for access by an SGI system. Of
course, the SGI uses a CDROM drive that uses 512 byte blocks. My desktop
PC's the only thing with a CD burner in it, which is naturally set to a
block size of 2048.
From the point of view of creating a CD, does this matter? Or is the
block size issue only to do with transferring data from the CD unit to
the host, and iso9660 is the same on both platforms?
It's one of those stupid questions that I really don't know the answer
to - I'm used to either just dealing with CDs on a PC, or using original
vendor media on systems which use 512 blocks (such as Sun and SGI)
I've only got a couple of decent branded blank CDs left in the house, or
I'd just risk trashing one and find out for myself :-)
Jerome Fine replies:
NOT a silly question at all!!
From what I have found, probably almost ALL CD-R(W)
media use a sector size of 2048 bytes.
When a block size of 512 bytes is required, usually the
CDROM drive (perhaps in conjunction with the controller
or host adapter) manages to make the conversion. This is
not a difficult as it sounds since ONLY read requests are
used.
My personal experience is that it is not trivial. While I understand
that Zane Healy has managed this with a PDP-11 system and is
able to use a CD in a suitable CDROM drive, I have not been
successful myself. BUT, I have never been take concerned or
motivated to sole the problem for a PDP-11 system.
However, using an emulator under Windows 98 SE on a
750 MHz Pentium III system with a standard motherboard,
I am successful in running old RT-11 software. To do so
requires the conversion from the 2048 bytes sectors to
512 byte blocks which are totally transparent as far as
a hard drive comparison is concerned. In fact, when I
recently acquired a DVD reader and the newest version
of E11, I am even able to read the first 64 blocks on the
CD (16 CD sectors) and boot RT-11 from the CD during
a test. The reason that I call it a test is because it is obviously
much easier to just use the ISO file for the CD and run that
file using the SIMH emulator.
What I am trying to say is that it may be necessary to
do something special, but the use of a CD when 512 byte
blocks are required for use with software which does not
understand 2048 byte sectors on a CD should not be
impossible if you can find a CDROM drive which will
take care of the problem for you.
Sincerely yours,
Jerome Fine
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