TI 990 architecture / was Re: TI-99/4A Floppies
ajp166 at bellatlantic.net
Wed Oct 3 14:26:08 CDT 2007
>Subject: Re: TI 990 architecture / was Re: TI-99/4A Floppies
> From: woodelf <bfranchuk at jetnet.ab.ca>
> Date: Wed, 03 Oct 2007 13:04:51 -0600
> To: General Discussion: On-Topic and Off-Topic Posts <cctalk at classiccmp.org>
>Peter C. Wallace wrote:
>> The registers-in-memory architecture might be suitable for a FPGA CPU
>> where BlockRAM (as system memory) is almost as fast as registers. Why
>> not have registers in memory instead of simulatiing it badly (and
>> expensively power wise) via caching, that is, why move data if you dont
>> have to?
There was a late version of 9900 that was done in I think bipolar or
some strange combo process that was many times faster than the
earlier machine be they NMOS or TTL. TI was not a MOS house for the
most part and were ahead by doing like PDP-8 and PDP11 putting their
earlier TTL machine on a chip. What they did wrong was to lag severely
in marketing and advancing the technology.
The 9900 was slow becuase at the time 2102s (fast ones were 400ns) were
slow. By 4 years later ram would be down to 45NS (2147 and 2167 as
examples). If the 9900 were to ramp up the clock as did the 8085 and Z80
by 1980 it would have gone from 2mhz to around 6-8mhz and that speed
increase would have made it from a pure performance standpoint, fast.
The speed would ahve been aciveable as the total transistor count on
the die was far lower than most (few registers) and the complexity
was fairly low. The sad story is they didn't.
The TI99/4a was a sad detour that really didn't show off the CPU
but did embody some interesing ideas. Grom was one.
>Simple registers are expensive. Look at the PDP-5. This is the 1960's
>when most architectures where developed. Even the PDP-10 I think
Registers were costly when a FlipFlop was an entire board. Then they
started to get two in a 16legged chip the cost was way lower and
the advantage of having more registers was nowhere near as costly.
Also PDP-5 was mid 60s and and we had PDP-10, PDP-11, CDC monsters
UNIVAC 1180s and VAX ahead of us at that date.
>was designed to use core memory as registers unless you want the
>optional module for F/F registers.
Your thinking pdp6 and earlier.
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