[Simh] pdp11 and unix

[Paul Koning]

> On Feb 27, 2016, at 5:09 PM, Johnny Billquist <bqt at softjar.se> wrote:
> 
> On 2016-02-27 20:57, Paul Koning wrote:
>> 
>>> On Feb 27, 2016, at 2:49 PM, Bill Cunningham <billcun at suddenlink.net> wrote:
>>> 
>>> Thanks much. Yes I know you were speaking of assembly. I was just considering history. I've always heard binary was first. What that might mean IDK. And there was no evidence presented for that.
>> 
>> It may just be a case of people not familiar with early documents, extrapolating from the fact that early programming was in machine language and many early machines were binary.  In other words, overlooking the fact that the use of octal or even decimal would be a pretty natural choice even right at the beginning.
> 
> Yes. In fact, from what I remember, decimal was used on many early computers. And you didn't really program them they way we think now. You didn't necessarily even have memory in the way we think now. Programming was done by connecting wires on large boards similar to telephone switches.
> 
> Octal is a natural extension once you go binary. But really early on, people obviously was thinking decimal, and thus the computers were too.

A couple of the earliest computers were indeed decimal, but binary was also used, and probably the majority.  And for good reasons; decimal arithmetic is MUCH harder, and the difference really shows up when you're implementing gates with dual-triode tubes.

ENIAC is a decimal machine (and a plugboard programmed one, i.e., not a Von Neumann computer).  But other very early machines were binary; for example, Booth's ARC machine, or the Manchester SSEM which Wikipedia says was the first Von Neumann computer.  EDSAC also. 

Decimal did show up at times even into the 1960s, for example in the IBM 1620.  But it never made all that much sense; converting between binary and decimal is quite easy even in those very old machines.  The one plausible application area is business data processing where the arithmetic is trivial and most of the work is I/O or other non-arithmetic operations.

I would assume there are lists of early computers and their characteristics such as binary vs. decimal.  

BTW, I think that plugboard programming, other than for some business applications with IBM "accounting machines", disappeared rather quickly as Von Neumann machines appeared.  That too would be interesting to look for.

	paul