23 Feb
2014
23 Feb
'14
11:25 a.m.
On 02/23/2014 07:37 AM, Liam Proven wrote:
On 22 February 2014 21:36, Terry Stewart <terry at
webweavers.co.nz> wrote:
It was slow not so much due to workspace but the fact that it ran code from
the 16K window that was video ram. That process was terminally slow.
It effectively stored interpreted code in video ram. Local ram was very
small,
512 words.
Having used the 9900 chip and also having a Technico super starter board
I can say it was as fast a many of the 8 bitter of the day (1978-79).
The 16 bit
architecture was very rich and had much better addressing modes.
The 99/4a was a unusual beast in that there was a lot of software but a
total failure.
and here is how I've described it on the
collections page:
http://www.classic-computers.org.nz/collection/ti99-4a.htm
Nice articles and an
impressive restoration!
I am not sure I've got the details right, but the significance of the
weird CPU of the TI99/4a might be worthy of a mention.
AIUI it was a low-end (single-chip?) version of an existing CPU, which
TI also used in much larger machines, right up to minicomputers.
Possibly the 99/4a's version was the first VLSI version or something.
(So a comparison with the PowerPC chip there - a single-chip
implementation of the IBM POWER architecture, an expensive multi-chip
UNIX server/workstation processor.) Also arguably bears comparison
with the BK Elektronica - that Soviet home-micro PDP-11.
But yes, as you say, the first 16-bit home micro - but very slow, in
fact slower than most 8-bits of its time period. AIUI part of the
reason for this is that the 99/4a CPU has no registers of its own,
uniquely among microprocessors - the registers are kept in main RAM,
meaning very slow bus accesses for /everything./
From the user standpoint practical use was hard as the
truncated keyboard
was not suitable for convenient word processing or other tasks
and the
32 or
40 char screen while colorful was not suitable for practical tasks. For
games
it was ok. All three versions I have use the same CPU the TI9900 in
the 64 pin
format.
Allison