bach@vax1.acs.udel.EDU (Baskaran Subramaniam) (07/06/90)
Is it possible to speed up an old 6Mhz IBM-AT (not a compatible) to 12Mhz by changing the crystal in it? We have an 80287/6Mhz and 512K RAM+1128K AST Rampage card in it. I think, the RAM chips have a speed of 120ns. Would changing the crystal create any problem with using these? Do I have to change the '287 and the RAM chips also? Do I have to change the '286 chip itself? I would appreciate any advice from the netters. Thanks, Baskaran.
sher@bbn.com (Lawrence D. Sher) (07/06/90)
In article <6692@vax1.acs.udel.EDU> bach@vax1.udel.edu (Baskaran Subramaniam) writes: >Is it possible to speed up an old 6Mhz IBM-AT (not a compatible) to 12Mhz >by changing the crystal in it? > >We have an 80287/6Mhz and 512K RAM+1128K AST Rampage card in it. I think, the >RAM chips have a speed of 120ns. Would changing the crystal create any problem >with using these? Do I have to change the '287 and the RAM chips also? Do I >have to change the '286 chip itself? Putting in a higher speed crystal will work, with increasing flakiness the higher the speed. My experience is limited, but I believe it is very unlikely that you will be successful at 12 MHz (24 MHz crystal). The "ISA" bus has a practical upper limit of just about 8 MHz. Even at 8.5 MHz, you may already find some intermittent trouble, like in the disk controller. I wouldn't try for more than 8.0 MHz.
amichiel@rodan.acs.syr.edu (Allen J Michielsen) (07/06/90)
In article <57993@bbn.BBN.COM> sher@labs-n.bbn.com (Lawrence D. Sher) writes: >In article <6692@vax1.acs.udel.EDU> bach@vax1.udel.edu (Baskaran Subramaniam) >>Is it possible to speed up an old 6Mhz IBM-AT (not a compatible) to 12Mhz >>by changing the crystal in it? >>We have an 80287/6Mhz and 512K RAM+1128K AST Rampage card in it. I think, th >>RAM chips have a speed of 120ns. Would changing the crystal create any probl >>with using these? Do I have to change the '287 and the RAM chips also? Do I >>have to change the '286 chip itself? >Putting in a higher speed crystal will work, with increasing flakiness the >higher the speed. >The Isa bus has >practical upper limit of just about 8 MHz. Even at 8.5 MHz, you may already >find some intermittent trouble, like in the disk controller. I wouldn't try >for more than 8.0 MHz. If the at bus has a practical upper limit of just about 8 Mhz, then all the clone 10 & 12 Mhz bus computers must not work. PC magazine had a article on doing this. Of course, the 286 & 287 will have to be scrapped. I too would be weary of taking a old war-horse 6 mhz at above 8 Mhz. But hey buy a 12 Mhz 286 (If you can find 1 with the right config--try harris) and try it. After getting a good max speed you'll be happy wiith, get a 287 to match it. When you get all done, if you pay yourslef $ 2 an hour ypou just spend more than it costs to get a new 12 mhz motherboard. But boy what a sense of self accomplishment you'll have. al
mats@infolog.se (Mats Lordin) (07/06/90)
> In article <57993@bbn.BBN.COM>, sher@bbn.com (Lawrence D. Sher) writes: > In article <6692@vax1.acs.udel.EDU> bach@vax1.udel.edu (Baskaran Subramaniam) writes: > Is it possible to speed up an old 6Mhz IBM-AT (not a compatible) to 12Mhz > by changing the crystal in it? > We have an 80287/6Mhz and 512K RAM+1128K AST Rampage card in it. I think, the > RAM chips have a speed of 120ns. Would changing the crystal create any problem > with using these? Do I have to change the '287 and the RAM chips also? Do I > have to change the '286 chip itself? I believe there might be some problems forcing your 80286 to run at speeds in which it was not designed for, the same might apply for the 80287. Please correct me if I'm wrong. -Madz
pajerek@usenet@kadsma (Don Pajerek) (07/06/90)
In article <3816@rodan.acs.syr.edu> amichiel@rodan.acs.syr.edu (Allen J Michielsen) writes: >In article <57993@bbn.BBN.COM> sher@labs-n.bbn.com (Lawrence D. Sher) writes: >>In article <6692@vax1.acs.udel.EDU> bach@vax1.udel.edu (Baskaran Subramaniam) >>>Is it possible to speed up an old 6Mhz IBM-AT (not a compatible) to 12Mhz >>>by changing the crystal in it? >>The Isa bus has >>practical upper limit of just about 8 MHz. > If the at bus has a practical upper limit of just about 8 Mhz, then all the >clone 10 & 12 Mhz bus computers must not work. >al A lot of clones run the processor at 12, 16, or 20 mHz, and the bus at 8 mHz. This does away with your objection. However, this doesn't help someone who just wants to take an existing 6 mHz AT and crank it up to 12. It probably won't work. Better stop at 8. Don Pajerek
sher@bbn.com (Lawrence D. Sher) (07/06/90)
>In <3816@rodan.acs.syr.edu> amichiel@rodan.acs.syr.edu (Allen J Michielsen) writes: >>In article <57993@bbn.BBN.COM> sher@labs-n.bbn.com (Lawrence D. Sher) writes: >>>In article <6692@vax1.acs.udel.EDU> bach@vax1.udel.edu (Baskaran Subramaniam) >>>>Is it possible to speed up an old 6Mhz IBM-AT (not a compatible) to 12Mhz >>>>by changing the crystal in it? >>>The ISA bus has a practical upper limit of just about 8 MHz. >> If the AT bus has a practical upper limit of just about 8 Mhz, then all the >>clone 10 & 12 Mhz bus computers must not work. Amazingly, the timing specs for the ISA bus have never been published! Look in with a logic analyzer and you will find that above 8 MHz, conventional circuits cannot reliably respond to *some* bus signals in the time available, like <15 nanoseconds. (This time is *not* inversely proportional to the bus speed. It is actually the difference between two times, the difference becoming negative at speeds in the vicinity of 10-12 MHz.) Consequently, if the computer has only one clock cycle time for both processor and bus, then 8 MHz is as high as one should reasonably dare. At 10 MHz, some 3rd party cards will definitely fail to work properly. The solution that has been widely adopted is to run the bus at 8 MHz and the processor at some higher speed. I believe that most (all?) 386-based ISA-bus machines do this. Since the basic 6 MHz IBM PC/AT Model 239 has only one cycle time for both bus and processor, simply changing the crystal is constrained by the timing needs of the bus. That, in turn, is constrained by the cards using the bus. You may be lucky enough to have cards that can work at 10 MHz, but don't count on it. Once you opt for a solution that uses multiple clocks, more upgrade paths become possible, but none of them can reliably run the bus faster than 8 MHz.
poffen@sj.ate.slb.com (Russ Poffenberger) (07/06/90)
In article <3816@rodan.acs.syr.edu> amichiel@rodan.acs.syr.edu (Allen J Michielsen) writes: >In article <57993@bbn.BBN.COM> sher@labs-n.bbn.com (Lawrence D. Sher) writes: >>In article <6692@vax1.acs.udel.EDU> bach@vax1.udel.edu (Baskaran Subramaniam) >>>Is it possible to speed up an old 6Mhz IBM-AT (not a compatible) to 12Mhz >>>by changing the crystal in it? >>>We have an 80287/6Mhz and 512K RAM+1128K AST Rampage card in it. I think, th >>>RAM chips have a speed of 120ns. Would changing the crystal create any probl >>>with using these? Do I have to change the '287 and the RAM chips also? Do I >>>have to change the '286 chip itself? >>Putting in a higher speed crystal will work, with increasing flakiness the >>higher the speed. >>The Isa bus has >>practical upper limit of just about 8 MHz. Even at 8.5 MHz, you may already >>find some intermittent trouble, like in the disk controller. I wouldn't try >>for more than 8.0 MHz. > If the at bus has a practical upper limit of just about 8 Mhz, then all the >clone 10 & 12 Mhz bus computers must not work. PC magazine had a article on >doing this. Of course, the 286 & 287 will have to be scrapped. I too >would be weary of taking a old war-horse 6 mhz at above 8 Mhz. But hey >buy a 12 Mhz 286 (If you can find 1 with the right config--try harris) >and try it. After getting a good max speed you'll be happy wiith, get >a 287 to match it. When you get all done, if you pay yourslef $ 2 an hour >ypou just spend more than it costs to get a new 12 mhz motherboard. But >boy what a sense of self accomplishment you'll have. >al Clones that run above 8Mhz attempt to stay compatible with the 8Mhz (most of them) by using a fraction of the CPU speed as the bus speed. As a matter of fact, my 25Mhz 386 system with C&T neat chipset has the ability to be programmed to set the bus speed to either AT clock speed (8Mhz), CPU speed / 3, or CPU speed / 2. I happen to run mine at CPU speed / 2 which equates to 12.5 Mhz and it works for me. A lot depends on the cards you have plugged in. Russ Poffenberger DOMAIN: poffen@sj.ate.slb.com Schlumberger Technologies UUCP: {uunet,decwrl,amdahl}!sjsca4!poffen 1601 Technology Drive CIS: 72401,276 San Jose, Ca. 95110 (408)437-5254
cramer@optilink.UUCP (Clayton Cramer) (07/07/90)
In article <6692@vax1.acs.udel.EDU>, bach@vax1.acs.udel.EDU (Baskaran Subramaniam) writes: > Is it possible to speed up an old 6Mhz IBM-AT (not a compatible) to 12Mhz > by changing the crystal in it? > > We have an 80287/6Mhz and 512K RAM+1128K AST Rampage card in it. I think, the > RAM chips have a speed of 120ns. Would changing the crystal create any problem > with using these? Do I have to change the '287 and the RAM chips also? Do I > have to change the '286 chip itself? > > I would appreciate any advice from the netters. > > Baskaran. When the AT first came out, it didn't take long to find out that the margins designed into the motherboard by IBM were enough to allow use of faster crystals, thereby speeding up the motherboard. As a general rule, the amount of speed-up you can get is variable from machine to machine. With three different ATs, we found different maximum speeds. One would run at 8Mhz, another at 10Mhz, and another at a speed just under 9Mhz. I didn't see any examples of IBM ATs that tolerated 12Mhz. Make sure that your RAM chips are fast enough to tolerate the higher speed, but if it's a genuine IBM, they PROBABLY will go faster. Note that the change in crystals is easy enough that if it doesn't work at 10, just change the crystal again. Make sure that the machine is COMPLETELY reliable before you commit yourself to that speed -- right at the hairy edge, some such systems would work for a few minutes, until you loaded in a large program, then failures would start to appear. -- Clayton E. Cramer {pyramid,pixar,tekbspa}!optilink!cramer Amtrak subsidies: adults playing with choo-choos. ---------------------------------------------------------------------------- Disclaimer? You must be kidding! No company would hold opinions like mine!
burton@mitisft.Convergent.COM (Philip Burton) (07/07/90)
In article <58011@bbn.BBN.COM> sher@labs-n.bbn.com (Lawrence D. Sher) writes: >>In <3816@rodan.acs.syr.edu> amichiel@rodan.acs.syr.edu (Allen J Michielsen) writes: >>>In article <57993@bbn.BBN.COM> sher@labs-n.bbn.com (Lawrence D. Sher) writes: >>>>In article <6692@vax1.acs.udel.EDU> bach@vax1.udel.edu (Baskaran Subramaniam) > >>>>>Is it possible to speed up an old 6Mhz IBM-AT (not a compatible) to 12Mhz >>>>>by changing the crystal in it? > >>>clone 10 & 12 Mhz bus computers must not work. > >Amazingly, the timing specs for the ISA bus have never been published! Look in >bus at 8 MHz and the processor at some higher speed. I believe that most >(all?) 386-based ISA-bus machines do this. > >of the bus. That, in turn, is constrained by the cards using the bus. You may >be lucky enough to have cards that can work at 10 MHz, but don't count on it. >Once you opt for a solution that uses multiple clocks, more upgrade paths >become possible, but none of them can reliably run the bus faster than 8 MHz. I own an original IBM 6 MHz AT. Years ago, people went wild when the discovered that the original 6 MHz AT was "really" supposed to run at 8 Mhz. A whole niche industry sprung up to replace the original issue AT crystals with faster models. I even spent money on two different solutions. The one I kept was from a company called Ariel, out of somewhere in NJ, I think. Using their product, I unplugged the standard crystal and replaced it with a twist-dial unit that could run the system from 6 to about 12.5 Mhz. My system always locked up at about 9.6 - 9.8 Mhz, but I couldn't tell why. My neighbor has an 8 Mhz AT, and he was able to run his system up to about 11.5 Mhz reliably. This was an unscientific comparison because we didn't try the same complement of adapter and memory cards, etc., in each system. --Phil Burton--
davidsen@sixhub.UUCP (Wm E. Davidsen Jr) (07/07/90)
In article <6692@vax1.acs.udel.EDU> bach@vax1.udel.edu (Baskaran Subramaniam) writes: | Is it possible to speed up an old 6Mhz IBM-AT (not a compatible) to 12Mhz | by changing the crystal in it? | | We have an 80287/6Mhz and 512K RAM+1128K AST Rampage card in it. I think, the | RAM chips have a speed of 120ns. Would changing the crystal create any problem | with using these? Do I have to change the '287 and the RAM chips also? Do I | have to change the '286 chip itself? You can increase the speed of the *old* AT by putting in a new crystal. The later ones didn't go any faster, but IBM put a check in the BIOS to generate an error in POST if you did it. Good marketing... build slow hardware and put the effort into ways to keep people from speeding it up! The RAM probably will run 8MHz, but I'd replace all of it with at least 100ns, maybe 80. RAM is just too cheap to take a chance. You will probably get something which doesn't woirk between 8-10MHz. It's usually the RAM, and if you go to better RAM you can often go a bit more. The CPU and FPU will probably run to 10MHz, but I would suggest putting a heat sink on at least the FPU. This is all stuff we did years ago. If it were mine I'd pull the motherboard and throw it away, and put in a 386SX with 2MB for about $500. Then it will all work, be within rated speed, and be reliable enough to be useful. The last time I pulled a few AT motherboards I posted them on misc.forsale as "best offer" and no one wanted them enough to make *any* offer. The world has moved on. -- bill davidsen - davidsen@sixhub.uucp (uunet!crdgw1!sixhub!davidsen) sysop *IX BBS and Public Access UNIX moderator of comp.binaries.ibm.pc and 80386 mailing list "Stupidity, like virtue, is its own reward" -me
emmo@moncam.co.uk (Dave Emmerson) (07/09/90)
In article <58011@bbn.BBN.COM>, sher@bbn.com (Lawrence D. Sher) writes: > >In <3816@rodan.acs.syr.edu> amichiel@rodan.acs.syr.edu (Allen J Michielsen) writes: > [deleted] > Amazingly, the timing specs for the ISA bus have never been published! > [more deleted] Actually, they have, but only just recently! I've seen a copy, but not for long enough to study it properly, so, for now at least, I'll go along with the rest of the article. Dave E.
beattie@MoFH.UUCP (Grant P. Beattie) (07/09/90)
> as one should reasonably dare. At 10 MHz, some 3rd party cards will definite > fail to work properly. The solution that has been widely adopted is to run t > bus at 8 MHz and the processor at some higher speed. I believe that most > (all?) 386-based ISA-bus machines do this. Agreed. The 386-20 on my desk runs with the bus speed normally at 10 Mhz, but it is switch selectable to 5 Mhz (mind you, I've never had a card that couldn't keep up at 10 Mhz except an old EPROM programmer).
cjdb@midway.uchicago.edu (Charles Blair) (07/14/90)
In article <57993@bbn.BBN.COM> sher@labs-n.bbn.com (Lawrence D. Sher) writes: >[...] My experience is limited, but I believe it is very unlikely >that you will be successful at 12 MHz (24 MHz crystal). The "ISA" bus has a >practical upper limit of just about 8 MHz. Even at 8.5 MHz, you may already >find some intermittent trouble, like in the disk controller. I wouldn't try >for more than 8.0 MHz. My own experience points to 8.2 or 8.3 MHz as the practical upper limit (I installed a variable speed crystal). I wasn't running the Rampage board, but the AST Advantage Premium. -- Bitnet: pmrcjdb@uchimvs1 Internet: cjdb@midway.uchicago.edu