10 Jun
2014
10 Jun
'14
8:47 a.m.
On 06/10/2014 01:47 AM, Eric Smith wrote:
As far as I know there wasn't any
"standard" CP/M 8-inch double-density
disk format, with many vendors doing their own, incompatible formats, but
was there any reason to prefer any one of those formats over any other? If
I hack my own BIOS, I can obviously do it however I want, but it seems like
it might be nice to be compatible with something.
The Quay boot ROM wants track 0 head 0 to contain eight 1KB sectors, but
since I'm hacking my own boot ROM anyhow, I'm not necessarily tied to that.
A quick survey of my library shows the 26x256 (IBM System/34) was a
common format, particularly among Japanese CNC makers. 15x512 and
8x1024 are also common. And there's the occasional 9x1024 and 17x512.
However, I do recommend that you not go with 128-byte MFM sectors--NEC
765-based controllers have a real problem with those due to an internal
bug. And do remember to include an IAM.
Other than that, remember that a larger sector size will require a
larger in-memory blocking/deblocking buffer. If you intend to equip the
unit with a hard disk, it's probably prudent to use the same sector size
on both floppies and fixed disks.
As to the logical organization of those sectors, there seemed to be no
consistently-used single one.
--Chuck