[Info-vax] C limitations, was: Re: VMS process communication

[Johnny Billquist]

On 2023-04-12 18:26, bill wrote:
> On 4/7/2023 4:58 PM, Johnny Billquist wrote:
>> On 2023-04-03 14:31, bill wrote:
>>>> PDP-8, as well as very old PDP-11 software usually also used mark 
>>>> parity on all characters. And as far as I know, the ASR-33 variant 
>>>> that DEC used did this, which might be the reason for all software 
>>>> doing it.
>>>
>>> I am not aware of any PDP-11 operating system where the charsets ASCII
>>> values were 128 to 255 as opposed to 0 to 127.  Certainly none where it
>>> was the hardware forcing it.
>>
>> XXDP (the PDP-11 diagnostics) are the oldest PDP-11 software I have 
>> been dealing with. A lot of code in there assumes you are running with 
>> mark parity, which basically means all output characters will always 
>> have the high bit set.
> 
> Yes, but there is a big difference between communications parity and
> memory parity.

Uh? Who mentioned memory parity? Not me.
This has all been communication, as such. But the data as such are 
generated already with mark parity by compilers. It's not something 
added by any hardware. And the parsing of received data is also done 
with the assumption that it was received with mark parity, and that is 
never stripped away.

   Johnny