Details about IBM's early 'scientific' computers

Rick Bensene rickb at
Wed Nov 15 15:57:37 CST 2017

On 11/15/2017 11:59 AM, Rick Bensene via cctalk wrote:

> While the definition of the term "personal computer"  varies depending 
> on who is using the term, these machines, and others like them, were 
> designed to be used at a much more personal level than the large-scale 
> mainframe machines housed in the glass-walled rooms where only "special"
> people were allowed anywhere near them.   

Chuck responded:

>How about "small systems", able to be powered solely from a 115V/20A source (or its 220V equivalent)?

>The PB 250 would certainly fall in this category also.

Indeed, a notable omission from my list.   

The PB 250 definitely is in that class of machine, and the unique part about it is that its main memory and register storage was made of recirculating delay lines.  This made the machine somewhat slow, but in most cases, a bit faster than most of the tube-based machines with magnetic drum memories.  The delay lines could be a little temperamental, but were less expensive than magnetic drums, making the machine a pretty good value for the time.  It was fully-transistorized, and had a Friden Flexowriter for I/O.  The machine had interfacing capabilities that allowed a number of various I/O devices to be connected to it.

The PB 250  benefitted from the design genius of Stanley Frankel, the Manhattan Project nuclear physicist that went into computing after his A-bomb development work had finished.  Frankel assisted with many of the design aspects of the PB 250, as well as doing the complete logic design of the LGP-30, which was based on a small machine he built on his own known as MINAC.  He also did the design of the SCM/Marchant Cogito 240 & 240SR electronic calculators, as well as the brilliantly-designed, microcoded Diehl Combitron electronic calculator.

Rick Bensene
The Old Calculator Museum

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