19 Feb
2019
19 Feb
'19
10:14 a.m.
On Feb 19, 2019, at 11:51 AM, Charles Anthony
<charles.unix.pro at gmail.com> wrote:
...
Presumably SIMH is returning RA81_LBN (891072) as the device size; this is calculated
based on the 51 sectors/track. If the h/w is returning a size based on 52, then there is a
mismatch which could be the source of the problem. It has been hypothesised that the
original problem is related to SIMH misreporting the disk size; I was trying to point out
a possible source of error; does anyone know what size the h/w reports?
-- Charles
Some people here probably have an actual drive and can double check.
Meanwhile, I found the "RA60, RA80, and RA81 disk drives" brochure (DEC, August
1982) on Archive.org. It has the details in the back. Page 36 shows "User data
capacity" and says 51 sectors, 14 tracks, 1248 cylinders -- that works out to 891072
sectors which is the number SIMH uses.
So indeed the correct sector count is 51 (the other one is a spare, a technique used by
DEC as far back as the RM80).
paul