10 Nov
2006
10 Nov
'06
10:31 a.m.
On 10 Nov 2006 at 11:54, Julian Wolfe wrote:
There's a utility called 'fastv20' that
speeds up NEC V20 chips, and fixes a
compatibility problem with them through software. I don't exactly remember
what it does to make it faster, since I don't have the docs in front of me
right now. It does do a pretty good job though!
It's a program based on an early PC magazine article about
"Supercharging the PC". It changes the DRAM refresh interval which,
because of the lower DMA traffic, gives a slight improvement in
speed, even on an 8088-equipped PC. Early DRAM varied quite a bit on
how long a chip could retain data between refreshes. (I remember
being surprised by some NEC 16K DRAMs hanging on to their data after
2 seconds without refresh).
You can tinker with refresh yourself. Here's the program source, in
all of its glory in debug form:
0100 B074 MOV AL,74
0102 E643 OUT 43,AL
0104 B08F MOV AL,8F
0106 E641 OUT 41,AL
0108 B002 MOV AL,02
010A E641 OUT 41,AL
010C CD20 INT 20
The instructions at 104 (low byte) and 108 (high byte) are the ones
to tinker with. I guess I wouldn't bother with the slight
improvement, but it was all the rage back then.
OTOH, replacing an 8088 with a V20 or an 8086 with a V30 is
worthwhile--the improvement in chip architecture does give a boost in
speed without risking anything--and gives you access to many of the
186/286 instruction set extensions, as well as a somewhat buggy 8080
emulation in hardware (e.g. JRT Pascal programs will die because of
an emulation bug).
Cheers,
Chuck