23 Feb
2014
23 Feb
'14
5:22 a.m.
On Feb 23, 2014, at 6:37 AM, Liam Proven wrote:
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./
That's part of the problem, yes, but not the only factor. It was a 16-bit CPU but the
designers of the system hobbled it with an 8-bit data bus. On top of this as you say the
only internal register it had was the workspace pointer register (and I think maybe the
PC? not sure about that), and then all the working registers were in system RAM...of which
it had a ridiculously small amount of... like < 512 bytes or so IIRC. All program
information was pulled off of GROMs (a special type of serial ROM in cartridge) and any
user programs on unexpanded systems was stored in video RAM.