Burroughs B5500 and successors (Was: Happy DEC-20 Day!)

[Alan Perry]

>
> From: "Jonas Otter" <jonas at otter.se>
> The architecture has so-called display registers, each of which pointed
> to a stack frame for a lexicographical level in the code, i.e. the
> procedure call level. Data is addressed as an address couple consisting
> of a display register number and an offset, stored in a so-called
> Indirect Reference Word (IRW). Data outside of the stack can be
> addressed by means of descriptors. Data in another program's stack is
> addressed by means of Stuffed Indirect Reference Words (SIRW), which
> include a stack number and an offset. The operating system keeps track
> of individual program stacks by means of a tree of pointers to job
> stacks. Also, to keep track of the procedure calling and return linkage,
> Mark Stack Control Words (MSCW) are created whenever a procedure is
> called. The Display Registers point to the MSCWs.
>   
Yes, that all sounds familiar.

Do you recall the sizes?
> All this is designed to support block-structured high level languages, in
> fact all the operating system software is (was) written in various ALGOL
> dialects.
>   
My favorite dialect was NEWP.  I particularly liked the UNSAFE directive.

I worked for Burroughs from just before the name change to Unisys 
(summer '86) to spring '89, my first job out of college.  I worked on A 
Series, V Series, B1000, BTOS and DOS stuff while I was there.  At 
school, I used BSD Unix on VAX and DEC-20, so the Burroughs stuff was 
really different (from stack machines to two-wire direct, poll/select 
terminals) and fun to play with and learn.

alan