On Sun, May 17, 2020 at 12:24 PM Paul Winalski <paul.winalski@gmail.com> wrote:
On 5/16/20, Steffen Nurpmeso <steffen@sdaoden.eu> wrote:
> Why was there no byte or "mem" type?

These days machine architecture has settled on the 8-bit byte as the
unit for addressing, but it wasn't always the case.  The PDP-10
addressed memory in 36-bit units.  The character manipulating
instructions could deal with a variety of different byte lengths:  you
could store six 6-bit BCD characters per machine word,

Was this perhaps a typo for 9 4-bit BCD digits? I have heard that a reason for the 36-bit word size of computers of that era was that the main competition at the time was against mechanical calculator, which had 9-digit precision. 9*4=36, so 9 BCD digits could fit into a single word, for parity with the competition.

6x6-bit data would certainly hold BAUDOT data, and I thought the Univac/CDC machines supported a 6-bit character set?  Does this live on in the Unisys 1100-series machines? I see some reference to FIELDATA online.

I feel like this might be drifting into COFF territory now; Cc'ing there.

or five ASCII
7-bit characters (with a bit left over), or four 8-bit characters
(ASCII plus parity, with four bits left over), or four 9-bit

Regarding a "mem" type, take a look at BLISS.  The only data type that
language has is the machine word.

>   +getfield(buf)
>   +char buf[];
>   +{
>   +       int j;
>   +       char c;
>   +
>   +       j = 0;
>   +       while((c = buf[j] = getc(iobuf)) >= 0)
>   +       if(c==':' || c=='\n') {
>   +               buf[j] =0;
>   +               return(1);
>   +       } else
>   +               j++;
>   +       return(0);
>   +}
> so here the EOF was different and char was signed 7-bit it seems.

That makes perfect sense if you're dealing with ASCII, which is a
7-bit character set.

To bring it back slightly to Unix, when Mary Ann and I were playing around with First Edition on the emulated PDP-7 at LCM+L during the Unix50 event last USENIX, I have a vague recollection that the B routine for reading a character from stdin was either `getchar` or `getc`. I had some impression that this did some magic necessary to extract a character from half of an 18-bit word (maybe it just zeroed the upper half of a word or something). If I had to guess, I imagine that the coincidence between "character" and "byte" in C is a quirk of this history, as opposed to any special hidden meaning regarding textual vs binary data, particularly since Unix makes no real distinction between the two: files are just unstructured bags of bytes, they're called 'char' because that was just the way things had always been.

        - Dan C.