29 Jul
2014
29 Jul
'14
2:18 a.m.
On Mon, 28 Jul 2014, Eric Smith wrote:
On Mon, Jul 28, 2014 at 11:21 AM, Mark Kahrs
<mark.kahrs at gmail.com> wrote:
Speaking of microcode and data paths: let's add the Dietz Mincal 523. It's
a very cleverly designed microprogrammed minicomputer (19 bit word
length) from around 1970 (the precursor was the Mincal 4 series). The most
exciting thing about it (apart from the odd word length) are 1. the
microcode lies in normal address space and 2. the copper trace/transformer
ROMs (some pics can be found on the preliminary page at
http://computermuseum.informatik.uni-stuttgart.de/dev/mincal523/).
Point 1 along with the fact that the macrocode (i.e. machine language)
registers are in core memory makes the machine incredibly slow, but makes
it possible to execute arbitrary microcode from core memory, too.
The machine has complex I/O and interrupt hardware suited for all kinds
of process control and the like, but the CPU itself consists of only
several not so big circuit boards with LSI TTL parts (I think the most
complex part are the five 7483 ALU ICs).
Christian
PS: I had to completely reverse-engineer the machine and microcode due to
the complete absence of any information on this machine.
Let me add that the PDP 11/44 was microcoded...
Specifically, it was used
by CMU to do C.mmp and Cm*.
I think you mean the PDP-11/40? IIRC, in addition to replacing the
microcode ROMs, they modified the hardware to add additional data
paths to make it more useful for the custom microcode.