>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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Received on Sun Jul 04 2004 - 21:39:22 BST