Byte sizes (was Re: 2.8M 3.5' floppy

Bjørn bv at
Tue Mar 15 13:46:12 CST 2005

On Tue, 15 Mar 2005 07:21:42 +0100, woodelf <bfranchuk at> wrote:

> William Donzelli wrote:
>>> Well the 1620 was a variable length machine ... A sign/flag bit made  
>>> more sence at the time since
>>> you only had as many BCD digits as you needed.
>> It is still very inefficient, with lots of wasted bits. It would not
>> matter with a small machine like a 1620, but it does when the system  
>> gets
>> larger. Even a small S/360 dwarfs a 1620. All those wasted bits add up.
> The 1620 is BCD serial ... slow but then lots less $$$ than a 360.
> Since I only got to know small computers like a PDP 8 and a IBM1130
> I never had to deal with the bigger stuff.

The 1620 was one of the first computers I used, but only at high-level  
Compiling was interesting - put the source cards in the reader, punch out  
an intermediate deck, then pass both through for the second pass. I used  
it for my physics lab tests, plotted nice graphs on the Calcomp drum  
plotter. We also had a line printer making 50 lines per minute. I never  
saw one like it, characters were on quarter-circle segments which rotated  
back and forth.

The Univac 1107 was a more impressive beast, with both a drum storage and  
a drum printer.
One of my major goofs was when I first used the drum, not knowing that it  
did not write any end of file marker.
Computer time was valuable in the sixties, and my program was reading from  
the drum for 20 minutes before the operator terminated it.

My favourite old big iron is the NCR 315. I worked for NCR Norway, who  
hade one in their data processing center. The 315 was, of course, a BCD  
system. It had 12-bit bytes (which were calles slabs, since the byte term  
was not established when it was new), and 24-bit words. I just found a  
couple of old pictures of the operator looking helplessly at a mess of  
magnetic tape. The really cool thing was that most of the input came from  
OCR - cash register journals written with National Optical Font. Scanned  
by a rotating drum with a tiny diamond-shaped opening and a  
photomultiplier inside.


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