> CD's are normally 1024 byte blocks 2048 Bytes/sector is the ISO std for CD-ROMs (Mode 1). Mode 2 omits ECC for2336 B/sector - but I don't know of a case where someone was crazy enough to use it for data.
> we might have done at DEC was mess with the block size on a CD DEC does not modify the physical sector format - it is implemented in the drive. VMS packs four 512 B logical sectors into one 2048 B physical sector; the driver handles buffering and provides the illusion of a 512B sector size. Most FILES-11 CDs use unmodified ODS-2. But distribution CDs would do things like omit (or truncate) the bit table to save space. For that reason, ANA/DISK would fail. There are some CDs that use a slightly modified HOM block (FILES-11 B Level 0), but it wasn't widely adopted. There are other oddities - drives & drivers tell different lies about the geometry (cyl/track/sector) of a CDROM; multiplying these out frequently will not match the file system's idea of the volume size. (As recorded in the SCB for FILES-11, equivalent for other formats.) The lies vary by OS, version, drive & phase of the moon. The same CD read under different conditions will report alternative facts. These will not trip up a DEC OS on DEC HW - but can create obscure issues with simulation - especially if you try to pass geometry from a physical drive thru SimH. Writing a CD is rarely supported by a standard driver - typically, CD writing software issues direct SCSI commands to the drive (encapsulated in whatever the real transport is). This may be by direct IO, or via a class driver. It can be somewhat tricky - note that most drives can not tolerate buffer underruns when writing. > I wasn’t able to figure out how to make it work in RSTS/E. To be bootable, a CD needs an appropriate boot block (LBN 0). For VMS, it's written by 'writeboot' - not initialize. I don't remember the details for RSTS - look at SAVRES->RESTORE and BACKUP for possibilities. Or wait for Paul K to fill that in. Also note that dual format CDROMs are possible - 9660 reserves the first 16 sectors for this; thus it's possible to write a disk that is readable as both FILES-11 and & 9660 (with file data being in the same sectors; only the metadata differs.) Such disks were actually created. On 01-Sep-18 15:28, Clem Cole wrote: > below... > > On Sat, Sep 1, 2018 at 2:39 PM Zane Healy <[email protected] > <mailto:[email protected]>> wrote: > > Create a virtual disk in SIMH the size of the CD-R blank. Prep > the disk, then burn it to CD-R. This is how I created my bootable > CD’s for RT-11 and RSX-11M+. I’ve then used those CD’s to do > installs on my PDP-11/73. I wasn’t able to figure out how to make > it work in RSTS/E. I could create the CD-R, but not boot and > install RSTS/E from it. > > > Just curious ... aren't there funnies because CD's are normally 1024 > byte blocks and disks are usually 512? IIRC, there are places that > store numbers of blocks (not bytes), and you have to be careful. I > have >>not<< played in any of that in years. > > IIRC one of things we might have done at DEC was mess with the block > size on a CD -- that's a Tim Litt type question. Those bits are so > long ago depreciated/garbage collected in my acitve brain cells. ;-) > ᐧ > _______________________________________________ Simh mailing list [email protected] http://mailman.trailing-edge.com/mailman/listinfo/simh
