27 Mar
1998
27 Mar
'98
11:22 p.m.
<Obviously this is meant to over clock the 286, with the rotary switch
<allowing increasing the clock frequency until the 286 fails.
Overclocking another retrorevionistpc idea.
No most likely it allowed you to buy the fastest 286 and clock it at it's
native speed.
<1) Does this really work? I thought you couldn't over clock a true AT?
< (This particular motherboard is a "256/512 K System Board" with
< piggy-backed RAM chips. It has lots of "ECOs" on the pin side of
< the board. I don't know if my other one does, too. Note: ECO =
< Engineering Change Order.)
The AT might go a little faster, at some point the DRAM timing goes flakey
and otehr things start to get cranky.
That's especially true of the ISA cards!
<2) Would increasing the 286-6 to a 286-8,10,12 increase the frequency
< at which it could reliably run? I have a PGA 286-8, but I'm not
< sure there are faster PGA 286s?
There are it went all the way to 12 or 16mhz. I have a LCC version thats
12 and the PS/2m50s I have are 10mhz.
<3) Any software needed? (The ROMs appear to be the same as on my other
< machine.)
None but the rams may get unhappy of pushed to fast (data takes time to
get out).
Allison
27 Mar
27 Mar
6:48 p.m.
Overclocking another retrorevionistpc idea.
Heh...just for fun value usually.
No most likely it allowed you to buy the fastest 286 and clock it at it's
native speed.
Right, that is best way. What I would do: find a PLCC socket and a
spare 286 12mhz CPU and plug them all in. Did that either way on
same pinout of either PGA oe PLCC packages. I liked especially
Harris C286 chips. Runs very cold even at full power. :) Simens is
HOTTEST, ow!
There was changes to bios to block o/c and that is why this device
went around this either by manual after post test or automatic.
Start up the machine at normal mhz, after post, crank up the clock
rate.
NOT really! the 14.38181mhz thingy take care of DMA, irq's and
ISA. In newer boards some changes the clock rate on the ISA by that
area also that o/c the whole ISA shebang. But the problem is with 2
specific chips that splits the clock feeds sometimes are rated at
specific clock rate.
Simply: change out those ram with lower nS rating using 256K x 1
chips for either type 1 or 2 motherboard. I did that for fun!
I preferred AT type 2 for compactness and low wait states, plug
either 100ns or 80ns ram, change cpu for 12mhz and watch the
operation. Someting might go cranky or you get a bit faster machine
but not by long shot.
That is why I prefer Model 50Z for no o/c required total package and
well tuned performance even I did not own one YET. I have a 286 12
motherboard 1' square clone that feels like type 1 8mhz board even
with fast ram. YUK.
Jason D.
PS: I wondered why I got a dud 286-8 cpu by IBM when I was given
boxful of junk parts. Don't think it was by o/c but CPU failures
how rare that are! :)
Allison
email: jpero(a)cgo.wave.ca
Pero, Jason D.
28 Mar
28 Mar
9:04 a.m.
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8:22 a.m.
Nah. It was done all the time on the original AT's which went from 6mhz to
8 in seconds.
However, IBM hacked up the new (8mhz model roms) to stop this from happening.
So, while IBM had 8mhz AT's until Microchannel the clones ran up to 20Mhz
286's. (Which beat early 386 16's at raw dos speed).
Bill
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10:54 a.m.
New subject: 286 Overclocking
In the summer of '86 I bought two 286 clones -- one for me, one for spouse
-- from Rose Hill Systems in Scotts Valley, CA. These were 8MHz, 1 MB RAM,
20 MB disk, 5.25 HD floppy, and 14" Quimax green-screens. The total bill
should have been $5,130 but the vendor discounted it to $5,000 flat.
The vendor himself gave me, in a Ziploc, the xtals to overclock these pups
to 10MHz, at which speed the base computers worked flawlessly. The 2MB AST
RAMpage card I installed in mine went flaky at the higher speed, and AST
said that fitting the new ROMs was a factory job; rather than pay AST's
price I sold the card and bought an Everex equivalent which handled 10MHz
with a shrug.
These were the machines that convinced me, my wife, and everyone who saw
them that clones were the wave of the future. We later sold one, but the
case of the other is still here with a running computer in it.
__________________________________________
Kip Crosby engine(a)chac.org
http://www.chac.org/index.html
Computer History Association of California
9849
days inactive
9850
days old
4 comments
5 participants
participants (5)
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allisonp＠world.std.com -
ard＠p850ug1.demon.co.uk -
engine＠chac.org -
jpero＠cgo.wave.ca -
pechter＠shell.monmouth.com