🚀 go-pugleaf

In article <817993224snz@jasper.demon.co.uk>
           mike@jasper.demon.co.uk "Mike Tomlinson" writes:

>In article <817942727snz@wookie.demon.co.uk>
>           wookie@wookie.demon.co.uk "John Beardmore" writes:
>
>> In article <817725354snz@jasper.demon.co.uk>
>>            mike@jasper.demon.co.uk "Mike Tomlinson" writes:
>> 
>> >I don't think this is the case: the 286 has a bug that makes it 
>> >possible to access to first 64k of memory above the 1Mb barrier, 
>> >and this was taken advantage of to allow DOS to be loaded high. 
>> 
>> But a 286 can access a lot more than 64k of extended memory. 16 meg once
>> out of real mode.
>> 
>> Anyway, that's an addressing mode, not a bug !  :)  It was quite rational
>> behavior that differed from an 8088 because the '88 didn't have enough
>> address lines to do it.  :)
>
>That's not the point: the 286 has a bug which allows the first 
>64k of extended memory to be accessible from *real mode*

Yup, I know it's real mode. No doubt the debate is still raging about
if this a bug or a feature...


> - in 
>other words, DOS can be loaded high on a 286 without the need to 
>switch into protected mode to access it,

Granted 64k or so of memory can be reached without a mode switch but is
that actually enough for dos and its data stuctures ?  I guess it might be
with command.com only being 50 something k.


> Switching into protected mode is done by a 
>kludge involving the keyboard controller, so it is inherently 
>slow.

Not as far as I recall. You are thinking of switching back to real mode
which is much harder.

Getting from real to protected mode is just a matter of setting a bit
in the machine status word as far as I recall.

And on the 286 there was always the LOADALL instruction which Intel
took the precaution of telling almost nobody about until the 286 was
almost obsolete !


>You've let NT spoil you... Get a 286 - get a life! <grin>

Got a 286 and a life. Granted the 286 has 11 meg of RAM and was a bit of a
brute in its day. Now it's got a clock doubling 286 to 486 CPU in it but
it's not really up to running win 95 in real time. Not if you've got a life
to get back to anyhow !  The time is comming when it won't even be fit for
comms !

It's not just NT that spoils you, it's the P/133 !

-- 
John Beardmore