John W Kennedy  <jwkenne@attglobal.net> wrote:
+---------------
| I said "machine language" and I meant it. I haven't touched a 1401 since 
| 1966, and haven't dealt with a 1401 emulator since 1968, but I can 
| /still/ write a self-booting program.
+---------------

Heh! I never dealt with a 1401 per se [except when running a 1410
in 1401 emulation mode to run the Autoplotter program, which wasn't
available for the 1410], but I still remember the IBM 1410 bootstrap
instructions you had to type in on the console to boot from magtape.

    v         v
    L%B000012$N

where the "v" accent is the "wordmark" indicator.

That says to read in a whole tape record in "load" mode (meaning
that wordmarks & groupmarks in memory are overwritten), synchronously
(stop & wait), from tape drive 0, starting at memory location
decimal 12, which, since the 1410 used *1*-based addressing,
was the location just after the no-op at location 11 above.

[Note that these are actual *machine* instructions, *not* "assember"!!
Like the 1401, the 1410 was a *character* machine, not an 8-bit-byte
binary machine. The bits in a character were named 1, 2, 4, 8, A, B,
and W (wordmark). Oh, and C, but that was character parity -- the
programmer couldn't set that separately.]

What was the corresponding 1401 boot sequence?

Oh, for the record, IMHO the DEC PDP-8 had a *much* simpler machine
language and assembler than the IBM 1401/1410.  ;-}


-Rob

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Rob Warnock			<rpw3@rpw3.org>
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