18 May
2020
18 May
'20
10:11 p.m.
On Sun, May 17, 2020 at 12:24 PM Paul Winalski <paul.winalski(a)gmail.com>
wrote:
On 5/16/20, Steffen Nurpmeso
<steffen(a)sdaoden.eu> wrote:
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
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, 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
characters.
Regarding a "mem" type, take a look at BLISS. The only data type that
language has is the machine word.
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.
+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.