Self modifying code, lambda calculus - Re: ENIAC programming

[Don North]

On 9/18/2015 9:51 PM, tony duell wrote:
>> The VAX-11/730 would have to have the microcode on TU58, as that is the
>> console media. Quite possible that it actually do load the microcode
>> from there at power up. I've heard that those machine were slow in so
>> many ways... :-)
> The 11/730 has no microcode ROM as far as I can see. However part of the
> instruction decoding is done in hardware, so implementing a totally different
> instruction set would be inefficient
>
> The craziest thing I have found in the 11/730 is that the control store is
> dynamic RAM (lots of 16K*1 chips). Every few milliseconds the CPU is
> halted while the control store is refreshed. There is space for 4K more
> of control store (1K of that is fitted if you have the integrated disk
> controller or floating point board) which is SRAM. Quite why the whole
> lot isn't SRAM is beyond me.
>
> -tony

Simple answer. The control store functionality had to fit in the available space 
on one hex
sized card, and 16K density DRAM was the only option. Allocating additional 
space to use
4K or 1K SRAM would have pushed the CPU design to an additional board, which was not
a design option at the time.

Don