[Info-vax] Moving away from OpenVMS

[Johnny Billquist]

On 2012-05-24 15:21, Ken Fairfield wrote:
> On Thursday, May 24, 2012 2:38:12 PM UTC-7, glen herrmannsfeldt wrote:
>> Phillip Helbig---undress to reply<helbig at astro.multiclothesvax.de>  wrote:
>>
>> (snip)
>>> So the 6-character limit for node names has another source (no pun
>>> intended) than the limit on a variable name in Fortran before
>>> Fortran90.
>
> DECnet node names.
>
>> Hmmm. Fortran was developed on 36 bit machines with a 6 bit
>> character set. (The IBM 704 and BCDIC.)
>>
>> DEC conveniently also build 36 bit machines that, in addition
>> to using ASCII (five per word) also used SIXBIT with six per word,
>> among other place for file names.
>>
>> It certainly wouldn't surprise me if node names could be traced
>> back to the PDP-10 (maybe TOPS-20), from there to its IBM ancestors,
>> and then to Fortran. But note that it would be that both traced
>> back to 36 bit machines, but no causal relationship between them.
>
> Yeah, I expect this goes back to the 36 bit machines.  DECnet
> is supported (first appeared?) on PDP-10, then that 6-character
> restriction was carried forward to VMS (and PDP-11 operating
> systems) so that all of them could talk to each other.

Nice try, but wrong. DECnet was initially developed on PDP-11 running 
RSX. The 36-bit machines were very much behind the leading edge during 
their whole time on DECnet. Eventually VMS became the leading edge, but 
it stayed with RSX for quite a while...

However, 6 characters also pack nicely into two 16-bit words, using 
Radix 50...

The PDP-10 often used 7-bit ASCII, packing five bytes to the word, yes. 
SIXBIT was used in lots of cases when a more restricted character set 
was enough, such as for symbols, filenames, usernames, and god knows 
what else. But it was also not totally unheard of to use 9-bit 
characters and pack 4 to a word. The PDP-10 had variable sized bytes, so 
they can be anything from 1 bit to 36 bits... Even nicer, even files 
(atleast in TOPS-20) actually know what bytesize they are in.

	Johnny