AOH :: REFRESH.TXT|
Altering RAM refresh rate for more speed
A PC refreshes it's RAM every 2mS. However, most modern RAM's can keep their
memory for up to about 1S without refreshing. The average PC spends about 7mS
per second on memory refreshing, so it is very easy to see that if you
decrease the time spent on refreshing, the more time for computation.
"... You can easily experiment on your own. Use DEBUG to change the frequency
of the 8253 timer that drives the DMA chip. A count of 900h loaded into the
8253's Timer1 gives a one second period.
The BIOS loads the count with 12h and the point of diminishing returns
comes around 30h or 40h. After 40h refresh happens so infrequently as to
have no effect on system performance. Benchmarks show no difference
between 40h and 900h.
A value of 40h gives a 2.6% speed increase on my Hollistan 186 board and a
5.8% increase on a standard 4.77 MHz 8088. I haven't had any problems using
this speedup. ...."
DEBUG session for altering RAM refresh rate.
C:>DEBUG ; invoke DEBUG
-A ; call the assembler
????:0100 MOV AL,74 ; configure 8253
????:0102 OUT 43,AL
????:0104 MOV AL,40 ; LSB for counter 1 ....
????:0106 OUT 41,AL ; change to alter refresh rate
????:0108 MOV AL,00 ; MSB for counter 1
????:010A OUT 41,AL
????:010C INT 20 ; back to DOS
????:010E ; <cr> exits assembler
-NREFRESH.COM ; name the file
-RCX ; file size stored in CX
:E ; file is E bytes long
-W ; write file to disk
Writing 000E bytes
-Q ; quit debug.
....... The above comes out of the Sept./Oct. 19887 issue of
I have tested the above programme on my PC, and my PC's performance
according to the Norton utilities has increased from 2.8 to 3.2.
That is for an 8MHz system with a V20 CPU.
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