Details about IBM's early 'scientific' computers

On 11/14/2017 11:20 AM, Chuck Guzis via cctalk wrote: Pretty much all computers of that early-60's vintage, where a maze of logic was used to decode instructions, and everything was done with discrete transistors and diodes, had quirky arcane instruction sets. Some of this was due to the prevailing thought on instruction sets, but part of it was done to save a few transistors here and there, and to heck with the side effects. Most of these computers had very few registers, or put the "registers" in fixed core locations, due to the cost of a flip-flop. The 709x series was certainly like that. Hard to BELIEVE, with 55,000 transistors! Well, microcode freed them from a lot of these constraints, instead of vastly convoluted decode and sequencing logic, the instruction set became just another computer program. If you compare the amount of logic in a 7094 and a 360/50, the 360 looks like a SIMPLE machine in comparison. I don't know how many transistors there were in a 360/50, but I'm guessing less than 20,000, maybe as little as 12,000. Even then, what they used for a FF (they called them D-latches) took 2.5 SLT modules each. Certainly, going from SMS to SLT, the machine got considerably smaller, but it seems that they got a lot simpler in architecture, as well. But, another current in computer architecture was to regularize the instruction set, what later came to be called orthogonality. The 360 certainly took that to heart. Also, getting rid of all those special purpose registers. The 709x and their ilk had accumulators, multiplier/quotient registers, index registers and all sorts of other things. The 360 just had "registers"! I think a major reason for this current was to make compiler writing simpler. But, it made life easier for the assembly language programmer, as well. Jon