[Info-vax] Assembly languages, was: Re: OT: PDP-11 history in arstechnica

[Simon Clubley]

On 2022-03-18, Johnny Billquist <bqt at softjar.se> wrote:
> On 2022-03-17 01:48, Simon Clubley wrote:
>> On 2022-03-16, Rich Alderson <news at alderson.users.panix.com> wrote:
>>>
>>> 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".
>>>
>> 
>> Doesn't anyone else find it strange that the mnemonic across all
>> architectures is some variant of MOVE or MOV instead of COPY or CPY ?
>
> You mean across all of these two (or three) DEC architectures (PDP-10, 
> PDP-11 and VAX)?
>
> Because some others use LOAD, LD, or some variant thereof. And then you 
> have (as mentioned) the PDP-8 which only have TAD (two complement add), 
> so if you want to read something out of memory, you better make sure the 
> AC is 0 before you do. Which of course is helped by the store 
> instruction which implicitly also clears the AC (DCA - Deposit and Clear 
> AC).
> And there are other things out there as well, if we talk about "all 
> architectures".
>

Yes, but that doesn't change my point that with every architecture
I know (both DEC and non-DEC) that uses a MOV/MOVE mnemonic variant,
then MOV/MOVE is actually a copy to destination instead as the source
is not destroyed during the copy.

Simon.

-- 
Simon Clubley, clubley at remove_me.eisner.decus.org-Earth.UFP
Walking destinations on a map are further away than they appear.