Extra chips in PDP11/23 plus cpu board

[Paul Koning]

> On Dec 20, 2017, at 1:16 AM, Nigel Williams via cctalk <cctalk at classiccmp.org> wrote:
> 
> On Wed, Dec 20, 2017 at 4:45 PM, Douglas Taylor via cctalk
> <cctalk at classiccmp.org> wrote:
>> There is a CPU board for sale on ebay, M8189, and it has the usual 3 chips
>> CPU, MMU, FPU.  However, there are 2 extra chips and I've never seen that
>> before.
> 
> https://en.wikipedia.org/wiki/PDP-11_architecture#Optional_instruction_sets
> 
> Microcode ROMs for the CIS (Commercial Instruction Set)

I believe PDP11 COBOL makes use of those if available, and the RSTS kernel will use the string move instruction for block memory copies if it sees CIS.

	paul