RK05/RL02 Boot Sequence

From: Tony Duell <ard_at_p850ug1.demon.co.uk>
Date: Fri Jul 2 18:16:17 2004

> Tony> Or from ROM (originally diode matrix [1]. later on bipolar PROM
> Tony> chips)
>
> Tony> [1] Chosen, I am told, because the user could program it
> Tony> without special equipment like a PROM programmer. All you
> Tony> needed was a pair of cutters (the 'blank' boards shipped with
> Tony> all the diodes fitted), and a soldering iron to correct errors.
>
> That's certainly a benefit. Another likely reason is that PROMs
> didn't exist yet (only, if anything, mask ROMs, which didn't make

Hmmm. The PDP11/45 used bipolar PROMs for the CPU and floating point
microcode. But the bootstrap board was a diode matrix. Now admittedly it
could have been designed for the 11/20 (which was a couple of years
earlier), and perhaps bipolar PROMs were not available then, but they
were certainly around in 1972.

> sense in quantities less than 1 million). And even if PROMs existed
> back then, 256 diodes were likely to be cheaper.

The board I am thinking of has 32 locations of 16 bits, so 512 diodes. I
have reprogrammed a couple...

-tony
Received on Fri Jul 02 2004 - 18:16:17 BST