Honeywall mainframe CPU front panel ID?
charles.unix.pro at gmail.com
Wed Jul 26 16:16:36 CDT 2017
On Wed, Jul 26, 2017 at 1:50 PM, Ed Sharpe via cctalk <cctalk at classiccmp.org
> define hardware diff. 635 and 645......ed#
Disclaimer: I wasn't there; this is my understanding from my work on the
The 635 was GE's flagship mainframe. 36 bit word, 256K word limit on
memory. No virtual addressing, but 'base and bound' addressing. (A
contiguous region of memory contain "user" program would be set up to
appear to it as it was occupying memory starting at address 0. Physically,
the memory would contain the operating system in low memory and user
programs in high memory. When the OS task switched to the user program, the
'base and bound' memory location made the user program appear to start at
address 0 and the operating system memory would be hidden (and protected)
The OS was GECOS (or GCOS), I forget which came first).
The Multics project selected the 635 as the base of a new machine and
worked with GE to develop the 645 to meet the needs of Multics; most
specifcally the "Append Unit" (APU) which implemented Multics' [unusual]
virtual memory model.
Functionally, the APU sits between the CPU and memory and maps virtual
addresses to physical ones. In reality, it invades the entire CPU; new
registers, new instructions, new addressing modes, the whole concept of
page faults, extending the maximum memory configuration from 256K words to
The 635 had two modes, absolute and BAR (base and bound). The 645 had a new
mode, "append" (and much to the consternation of the emulator developers,
also 'append with base and bound'; Multics uses that mode to run GCOS
programs in a GCOS emulator).
In absolute and BAR modes, the 645 is quite similar to the 635, but once
you switch to append mode, it gets pretty wild.
At some point in the evolution from the 635 to the 6180, the instruction
set was extended with string and decimal math operations: Extended
Instruction Set (EIS). I don't know the timeline or model designations.
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