4 Oct
2020
4 Oct
'20
1:50 p.m.
On Friday, October 2, 2020 at 13:51, Al Kossow via cctech wrote:
Those would already be broken with Bob's use of
large negative numbers
for physical end of tape and 'bad block is here' (you don't get to know
how big that bad block was, so that is hell with tapes with
variable-length records, grumble..)
I'm not sure I understand. SIMH metadata markers are treated in the tape
library code as unsigned values, so EOM and erase gap are seen as large
unsigned values. The format limits record lengths to 24 bits (so about 16
MB maximum per record), reserving the upper 8 bits to indicate the type of
the marker, and the bad record marker is the top byte = 0x80. The record
length of a bad block is encoded in the lower 24 bits and indicates how big
the bad block was.
What am I missing?
-- Dave