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From: eepjm@cc.newcastle.edu.au
Newsgroups: alt.msdos.programmer,comp.sys.ibm.pc.misc,aus.computers.ibm-pc
Subject: Setting the Turbo mode by software
Message-ID: <1991Apr10.104737.9962@cc.newcastle.edu.au>
Date: 10 Apr 91 00:47:37 GMT
Organization: University of Newcastle, AUSTRALIA
Lines: 28

My apologies to those who have seen this before - it looks as if I gave my
original posting too restricted a circulation, because the only replies I
got were from those who didn't know the answer.

Background: on many IBM-AT clones, one has a "turbo" mode or something similar
to select the processor clock rate.  On some such machines the switching is
obviously hard-wired since the only way to change the speed is with a
front-panel pushbutton.  On many others, however, the speed can be changed
via the keyboard (using Ctrl/Alt/+ or something similar), which implies that
the speed can be changed by software.

Question: how does one do this?  Presumably by writing something to a port,
but which port and what is the code?

(Yes, I know that the answer might be different for different clones, but
 if I can find out the answer for at least one clone, that gives me a
 starting point.  And you never know, a de facto standard might have arisen.)

While I have your attention, here's another tricky question to which I
would love to have the answer:

How does one tell MS-DOS that it's in-memory copies of a disk FAT and
directory are invalid - i.e. how can one force it to re-read the disk rather
than rely on its obsolete in-memory copy?  Re-booting the machine works
(but by then it's usually too late, another disk-full of vital files has
been corrupted), but I'd like to have a less drastic solution.

Peter Moylan                    eepjm@cc.newcastle.edu.au