17 Dec
2009
17 Dec
'09
7:21 p.m.
On Wed, Dec 16, 2009 at 2:05 PM, Tony Duell <ard at p850ug1.demon.co.uk> wrote:
Sure. And there were also commands (which I have used) to read/write
locations of the interface processor address space (at least on the
IEEE-488 units which have 2 processors in them, one to handle the
interface, the other to handle the disk data).
I can;t see why that would be a problem. The HP
protocols are all block,
not file, baeed (unlike the Commodore drives for the PET). The drive
doesn't have any idea what OS is talking to the it, it has no
understanding for the directory or the filesystem.
While Commodore disks do indeed have a firmware "DOS" that handles
file-level access and formatted directory listings and such, the
firmware fully supports block-level access by the B-R/B-W (or U1/U2)
commands. Infocom used that method for their VM implementation for their Z-machine (once you used "CBM DOS" to
read in a ~700 byte
bootstrap loader).
It's a fully-manual scheme - you tell the disk drive to read track X,
sector Y into a buffer, then issue a Memory-Read command to pull the
bytes out, or Memory-Write to stuff bytes in, then tell the drive to
write that buffer back out to wherever on the media you prefer.
My point was that on the HP drives, _all_ you have is the block access.
The HP drives have no internal filesystem (the commodore ones do, but as
you say you don't have to use it).