RK05 size and DEC systems

[utzoo!decvax!duke!bcw]

Correction to Dennis Rockwell's comment that DEC software uses
the last 72 of the 4872 blocks on an RK05 for bad block
replacements:  DEC software does bad block replacement by
creating files which "use" the bad blocks, not by pointers to
"spare" blocks at the end of the disk.  That was the original
purpose behind the extra 72 blocks, but as usual the hardware
people weren't talking to the software people.  In fact, the
extra 72 blocks aren't really useable as spares because there
is no hardware assist in the drive (as there is on certain
fixed-head drives) so that the software still has to intervene
and might as well use the DEC software people's scheme.

Why the extra 72 blocks aren't actually used is probably just
pure stupidity.

			Bruce C. Wright @ Duke University