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

[chris]

On 03/19/22 01:21, gah4 wrote:
> On Friday, March 18, 2022 at 12:22:10 PM UTC-7, Simon Clubley wrote:
>
> (snip)
>
>> 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.
>
> In the case of overlapping operands, the source might get,
> at least partially, destroyed.

The whole original point that was being made was that for sequences
like mov (a5)+. (a5), the (A5)+ always completes before the store to
(A5). That's how one would expect it to work, but it does require
a scratchpad store for the result of the first half of the expression.

Vax and pdp11 would work that way, as would later micros like 68000...

Chris



>
> In the days of magnetic core memory, which has a destructive read
> cycle, one could have designed processors that did clear the source.
>
>