Path: utzoo!attcan!utgpu!watmath!iuvax!purdue!mentor.cc.purdue.edu!l.cc.purdue.edu!cik
From: cik@l.cc.purdue.edu (Herman Rubin)
Newsgroups: comp.arch
Subject: Why 36 bits.
Summary: Interesting reasoning, but wrong.
Message-ID: <1451@l.cc.purdue.edu>
Date: 28 Jul 89 12:49:08 GMT
References: <355@torsqnt.UUCP> <3490016@wdl1.UUCP>
Organization: Purdue University Statistics Department
Lines: 29

In article <3490016@wdl1.UUCP>, bobw@wdl1.UUCP (Robert Lee Wilson Jr) writes:
> And note that the tube type machines from which the 709x evolved were also
> 36 bitters, and in turn that 36 is a nice multiple of 12 which is the
> number of rows in an "IBM" card. Since old machines like the 704/701 read
> cards as binary images into core, and translated bit patterns into
> (EBCDIC) characters via internal software rather than something in an I/O
> channel, this was not a coincidence!
> The past marches on!
> Bob Wilson
> (bobw@wdl1.fac.ford.com)

This reasoning happens to be totally false.  It was not until much later
that cards were read by columns.  The 704 and 709, certainly read by ROWS,
not columns.  The first word read was the left 36 bits of the 9's row,
the next bits 37-72, then the left 36 bits of the 8's row, etc.  The
right 8 columns were not read at all; this is the reason why Fortran
used only 72 columns.

The early computers used 6-bits (some even 5) per character.  Thus 36
bits was 6 characters.  The standard tapes were 7 tracks including parity.
There were several 6 bit character codes on different machines.

The CDC 1604 and 3600 were 48 bits, and the CDC 6x00 was 60 bits.  These
machines only had upper case, and 6 bit character sets.  They did use the
more efficient column binary.
-- 
Herman Rubin, Dept. of Statistics, Purdue Univ., West Lafayette IN47907
Phone: (317)494-6054
hrubin@l.cc.purdue.edu (Internet, bitnet, UUCP)