3 ms·

Oh, I bet you'd have loved the TMS 9900. Tons of registers with switchable windows, mini-computer oriented ... and big-endian.

ggm 3y ago
Looks good, but from a business perspective, another dead end -What I read says TI decided to get out of the general CPU business. Probably it means they couldn't find somebody interested in buying into this ISA and chipset to sustain their investment in developing it, where they had solid business in the other specialised spaces. Yes, heaps of registers which map into the address space means (I am guessing) simple C compiler and Unix porting, once virtual memory is there. I wonder why nobody ran with it?
- FullyFunctional 3y ago
  The TI-99/4A was atrocious on many level, but the reason for the abysmal performance is well documented on Wikipedia -- the architecture was inherited from TI-990 which assume fast 16-bit memory and TMS9900 had neither.
- canucker2016 3y ago
  Looking at the specs for the TI TMS9900, Zilog Z80, and the MOS 6502, the TI chip came in a 64-pin DIP and required +5V, -5V, and +12V power supply while the other two chips came in a 40 pin DIP package and only required a +5V power supply. The 6502 was cheap (<$30), the Z80 was more expensive at introduction, but looking at price lists, dropped down close to the same price as the 6502 within a few years. from https://www.cpushack.com/2015/02/05/ti-tms9900sbp9900-accidental-success/ https://www.cpushack.com/2015/02/05/ti-tms9900sbp9900-accide...: " In 1978 a 9980 cost $30 while a TMS9900 cost $70." Also, in the comments from the above link: "Many years later, the processor architect for the TMS9995 (Karl Guttag) pointed out to me that whatever context switch benefits the WP offered were quickly outweighed by the required memory access cycles only a handful of instructions into an interrupt service routine. It was a false economy."

ggm 3y ago

Looks good, but from a business perspective, another dead end -What I read says TI decided to get out of the general CPU business. Probably it means they couldn't find somebody interested in buying into this ISA and chipset to sustain their investment in developing it, where they had solid business in the other specialised spaces. Yes, heaps of registers which map into the address space means (I am guessing) simple C compiler and Unix porting, once virtual memory is there. I wonder why nobody ran with it?

FullyFunctional 3y ago
The TI-99/4A was atrocious on many level, but the reason for the abysmal performance is well documented on Wikipedia -- the architecture was inherited from TI-990 which assume fast 16-bit memory and TMS9900 had neither.
canucker2016 3y ago
Looking at the specs for the TI TMS9900, Zilog Z80, and the MOS 6502, the TI chip came in a 64-pin DIP and required +5V, -5V, and +12V power supply while the other two chips came in a 40 pin DIP package and only required a +5V power supply. The 6502 was cheap (<$30), the Z80 was more expensive at introduction, but looking at price lists, dropped down close to the same price as the 6502 within a few years. from https://www.cpushack.com/2015/02/05/ti-tms9900sbp9900-accidental-success/ https://www.cpushack.com/2015/02/05/ti-tms9900sbp9900-accide...: " In 1978 a 9980 cost $30 while a TMS9900 cost $70." Also, in the comments from the above link: "Many years later, the processor architect for the TMS9995 (Karl Guttag) pointed out to me that whatever context switch benefits the WP offered were quickly outweighed by the required memory access cycles only a handful of instructions into an interrupt service routine. It was a false economy."