[Simh] pdp11 and unix

[Paul Koning]

> On Feb 26, 2016, at 7:13 PM, Clem Cole <clemc at ccc.com> wrote:
> 
> 
> On Fri, Feb 26, 2016 at 6:28 PM, Nigel Williams <nw at retrocomputingtasmania.com> wrote:
> Perhaps not unusual for the 1960s but laborious none-the-less.
> 
> ​Depends who you are.   For grins look for the original Cray-1 "assembler" box.   You'll discover there are no mnemonics like "add", "branch" - just octal codes.   Seymor didn't need them. ​

Obviously, to get an assembler you'd first have to bootstrap *that*, unless you could write a cross-assembler.  And early assemblers weren't necessarily all that fancy.  

I've been reading some 1950s era computer descriptions, for machines without assemblers.  Opcodes are simply written as op/addr so you'd remember, say, that 0 is add and 6 is store, and so forth.  A machine introduced in Holland in 1958 -- the EL-X1 -- had a very bare-bones assembler, or slightly smart loader, depending on how you'd want to think about it.  Just a few hundred instructions; it had opcodes like "0A" (add to A) or "6S" (store S register).  And it had symbolic addresses, but you couldn't label individual locations, only "paragraphs" because symbols were only pairs of one of 13 letters, i.e., a max of 169 symbols per program.  Still, with that primitive tool some large software was written, such as the world's first ALGOL compiler.

It isn't really all that much harder than a modern assembler once you get used to the different look.

	paul