[Info-vax] OT: PDP-11 history in arstechnica

[Rich Alderson]

gah4 <gah4 at u.washington.edu> writes:

> On Monday, March 14, 2022 at 7:18:27 PM UTC-7, Rich Alderson wrote:

> (snip of DEC syntax)

>> "DEC" syntax, hmm? Macro-10: 

>> MOVE 17,SUMWHR 
>> ADDI 17,37 
>> MOVEM 17,ELSWHR 

>> The "destination" AC always follows the opcode immediately, the effective 
>> address of the "source" comes after the comma. Note that since there are 
>> "to-memory" instructions, the notion of "source" vs. "destination" is not 
>> particularly useful... 

> For IBM S/360 and successors, it is right to left, except for store instuctions,
> which usually (or always) have opcodes starting with ST.  That makes them
> easy to recognize.

> PDP-10 "to-memory" instructions are not so easy to recognize.

Nonsense.

ALL the PDP-10 mnemonics for instructions which access memory have the same
form (taking MOVE as a canonical example):

	MOVE	load accumulator with contents of memory at effective address
	MOVEI	load accumulator with immediate effective address calculation
	MOVES	load accumulator with swapped halfwords of contents of memory
		at effective address
	MOVEM	store accumulator into memory at effective address

Look at the last character of the instruction.  You don't even have to remember
the difference between "load" and "store".

-- 
Rich Alderson					  news at alderson.users.panix.com
      Audendum est, et veritas investiganda; quam etiamsi non assequamur,
	  omnino tamen proprius, quam nunc sumus, ad eam perveniemus.
									--Galen