>From: Johnny Billquist <bqt@update.uu.se>

>> Potential nitpick:  I don't know about bad144 the *program*, but the
>> Massbus-style last-track bad block file is also used on the RK06/RK07,
>> and (sort of) on the RL01/RL02 (minus the 18-bit copies).
>
>18-bit copies?
>Ah, perhaps you're talking about if the packs are used for -18(36) bit
>systems. Hmmm, I think you really need to reformat the packs to use them
>on the other system, and thus need to rewrite the bad block list.

I've never seen the actual DEC spec for this, just the stuff in the RK07
manual, so I may be wrong but my understanding is:  the last track (with
the bad block file on it) is always formatted in 16-bit mode even when
used on an 18-(36-)bit system.  There are two copies (actually, many copies
of each, but two *sets*) of the bad block file, one of which shows which
sectors are bad when the pack is formatted in 16-bit mode, the other shows
where the bad spots land when you format the pack in 18-bit mode.  The
RL01/RL02 has no 18-bit mode so they omit all the 18-bit stuff in the bad
block file.

The RK06/RK07 *does* support 18-bit mode but, does anyone know of a system
which actually used it?  I don't think the 10s or 20s ever did (DM:s are
really too small for them anyway), but I thought I read somewhere that the
PDP-15 had a Unibus (option?), could that be it?

John Wilson
D Bit