tea6219@evtprp0b (Terry E. Acker) (07/10/90)
I know there has been a similar discussion about 80287's, but I need related info on the 8087: I have an XT with a V20 processor running at 8/4.77Mtz. What speed coprocessor do I need. If there are different speed 8087s, can I use a 4.77Mtz 8087 and set the system speed to 4.77? What if I run the system at 8Mtz with a 4.77Mtz 8087? Will it work? Will it overheat? Thanx in advance!
sonny@charybdis.harris-atd.com (Bob Davis) (07/11/90)
In article <169@evtprp0b.UUCP> you write: >I know there has been a similar discussion about 80287's, but I >need related info on the 8087: > >I have an XT with a V20 processor running at 8/4.77Mtz. What speed >coprocessor do I need. If there are different speed 8087s, can I >use a 4.77Mtz 8087 and set the system speed to 4.77? What if I run >the system at 8Mtz with a 4.77Mtz 8087? Will it work? Will it >overheat? > >Thanx in advance! 8087's run synchronous with the CPU. Therefore, if you want to run at 8 MHz, you need an 8 MHz 8087. When you are running a 4.77 MHz 8087, there is no possibility at all of having it run at 8 MHz. It is not merely a matter of the chip overheating: it simply will not be able to keep up with the fast clock rate. It will stumble and drop clock pulses and just royally fail. It will be totally useless. So, if you want to run at 8MHz, you must have an 8 MHz 8087. 80387's share with the 8087 this trait of the coprocessor clock operating synchronous with the CPU clock. 80287's, on the other hand, do not HAVE to be operated synchronous with the 80286 CPU. Most often, in fact, the 80287 is clocked at 2/3 the CPU rate - but this is more convention than requirement. As I understand it, one may buy whatever rate 80287 one wishes, and if you can find a clock on the motherboard to clock it with (or you can provide your own), you can run it at that rate. Good luck... ______________________________________________________________________________ Bob Davis \\\INTERNET : sonny@trantor.harris-atd.com | _ _ | Harris Corporation, ESS \\\ UUCP : ...!uunet!x102a!trantor!sonny |_| |_| | | Advanced Technology Dept.\\\AETHER : K4VNO |==============|_/\/\/\|_| PO Box 37, MS 3A/1912 \\\VOICE : (407) 727-5886 | I SPEAK ONLY | |_| |_| | Melbourne, FL 32902 \\\ FAX : (407) 729-2537 | FOR MYSELF. |_________|
mussar@bcars53.uucp (G. Mussar) (07/12/90)
In article <169@evtprp0b.UUCP> tea6219@evtprp0b (Terry E. Acker) writes: >I have an XT with a V20 processor running at 8/4.77Mtz. What speed >coprocessor do I need. If there are different speed 8087s, can I >use a 4.77Mtz 8087 and set the system speed to 4.77? What if I run >the system at 8Mtz with a 4.77Mtz 8087? Will it work? Will it >overheat? If you plan on always running at 4.77 MHz, no problem. If you switch to 8 MHz, chances are the system won't even boot/run. This is based on trying the same experiment with a 4.77/10 MHz XT. YMVM. Even if if does boot/run, the 8087 (which normally runs pretty warm) will run VERY hot and this will decrease its life significantly. -- ------------------------------------------------------------------------------- Gary Mussar |Bitnet: mussar@bnr.ca | Phone: (613) 763-4937 BNR Ltd. | UUCP: ..uunet!bnrgate!bcars53!mussar | FAX: (613) 763-2626
klh@mtune.ATT.COM (Ken Hinds) (07/12/90)
From article <1990Jul11.172043.525@bigsur.uucp>, by mussar@bcars53.uucp (G. Mussar): > In article <169@evtprp0b.UUCP> tea6219@evtprp0b (Terry E. Acker) writes: >>I have an XT with a V20 processor running at 8/4.77Mtz. What speed >>coprocessor do I need. If there are different speed 8087s, can I >>use a 4.77Mtz 8087 and set the system speed to 4.77? What if I run >>the system at 8Mtz with a 4.77Mtz 8087? Will it work? Will it >>overheat? > > If you plan on always running at 4.77 MHz, no problem. If you switch to 8 MHz, > chances are the system won't even boot/run. This is based on trying the same > experiment with a 4.77/10 MHz XT. YMVM. Even if if does boot/run, the 8087 > (which normally runs pretty warm) will run VERY hot and this will decrease its > life significantly. Well, I have a dual speed 8088 micro processor in my Leading Edge Model D and I have added an 8087 math coprocessore but, it is listed as an 8087-2 which implies dual speed... Sorry I don't recall the manufacturer but, I'm sure you could find it if you ask for it specifically. ============================================================== Kenneth Hinds _ _ AT&T DSG Lincroft,NJ ' ) ) ' ) ) / UUCP: ...!att!mtune!klh /--' _ ,_ /--/ @ ,_ __/ klh@mtune.att.com / \_</_/) ) / \/ /_/) )_(_/\/)_ ==============================================================
johnv@metaware.metaware.com (John Vinopal) (07/13/90)
> Stuff about 8087's overheating deleted.
It is common (risky) practice to overdrive chips. There were 25Mhz 386 boxes
long before the i386-25 was released. Why then can this not be done with the
387 chips? I have heard that at least with the 287s the chips are all basically
the same but they have been verified at different clock speeds. Thus an 8Mhz
is no different than a 10Mhz, but for the fact that the 10 is guarenteed to
work at 10. Could someone expand on why a 25Mhz 387 could not be used in a
33Mhz box? If overheating is the only problem then whats the deal, install a
cooling system.
johnv@metaware.comjohn@wa3wbu.UUCP (John Gayman) (07/14/90)
In article <169@evtprp0b.UUCP>, tea6219@evtprp0b (Terry E. Acker) writes: > > I have an XT with a V20 processor running at 8/4.77Mtz. What speed > coprocessor do I need. If there are different speed 8087s, can I > use a 4.77Mtz 8087 and set the system speed to 4.77? What if I run > the system at 8Mtz with a 4.77Mtz 8087? Will it work? Will it > overheat? > Unlike the 286 machines, your coprocessor runs at the same clock speed as your 8088 or it your case V20. So if buying a 8087 you want to get one designed for the highest clock rate you'll be running.... 8 Mhz. You *could* if you so desired, purchase a 4.77 Mhz chip and run your machine at the slower clock rate. I ran into an interesting situation regarding 8087's. When I bought my first XT-class machine way back when it was to be a standard 4.77 Mhz unit. I had applications which insisted on a coprocessor. So I ordered ahead of time a 4.77 Mhz 8087. When my machine arrived, low and behold there was a note telling me they were shipping "turbo" machines (8 Mhz) at no extra charge. I could not return the 8087 for a faster one so I put it in anyway. I ran that machine that way for about 3 years. I can't really advise you to intentionally buy a slower chip and run it at the faster speed but if you alread have a chip I would certainly try it. In my case had I known I would be getting a 8 Mhz unit, I would have purchased a 8 Mhz 8087. John -- John Gayman, WA3WBU | UUCP: uunet!wa3wbu!john 1869 Valley Rd. | ARPA: john@wa3wbu.uu.net Marysville, PA 17053 | Packet: WA3WBU @ WB3EAH
kdq@demott.COM (Kevin D. Quitt) (07/17/90)
In article <673@mtune.ATT.COM> klh@mtune.ATT.COM (Ken Hinds) writes: > >Well, I have a dual speed 8088 micro processor in my Leading Edge >Model D and I have added an 8087 math coprocessore but, it is listed >as an 8087-2 which implies dual speed... ^^^^^^^^^^ Uh, not quite. The -2 states that the chip has a maximum rated speed of 8MHz. -1 means 10 MHz. -- _ Kevin D. Quitt demott!kdq kdq@demott.com DeMott Electronics Co. 14707 Keswick St. Van Nuys, CA 91405-1266 VOICE (818) 988-4975 FAX (818) 997-1190 MODEM (818) 997-4496 PEP last 96.37% of all statistics are made up.
mussar@bcars53.uucp (G. Mussar) (07/18/90)
In article <673@mtune.ATT.COM> klh@mtune.ATT.COM (Ken Hinds) writes: >Well, I have a dual speed 8088 micro processor in my Leading Edge >Model D and I have added an 8087 math coprocessore but, it is listed >as an 8087-2 which implies dual speed... Sorry I don't recall the >manufacturer but, I'm sure you could find it if you ask for it specifically. > >============================================================== >Kenneth Hinds >AT&T DSG Lincroft,NJ >UUCP: ...!att!mtune!klh Sorry, close, but no cigar. An 8087-2 does not signify a dual speed part. The suffix indicates the maximum rated speed of the part. Of course you can run them slower than maximum rated speed if you wish. 8087 - 5 MHz 8087-2 - 8 MHz 8087-1 - 10 MHz -- ------------------------------------------------------------------------------- Gary Mussar |Bitnet: mussar@bnr.ca | Phone: (613) 763-4937 BNR Ltd. | UUCP: ..uunet!bnrgate!bcars53!mussar | FAX: (613) 763-2626
browner@rm1.UUCP (Michael Browner) (07/20/90)
In <673@mtune.ATT.COM> klh@mtune.ATT.COM (Ken Hinds) writes: >Well, I have a dual speed 8088 micro processor in my Leading Edge >Model D and I have added an 8087 math coprocessore but, it is listed >as an 8087-2 which implies dual speed... Sorry I don't recall the >manufacturer but, I'm sure you could find it if you ask for it specifically. The 8087-2 does not imply dual speed the -2 designation means the chip will run the 8Mhz. The 8087-1 will run 10Mhz, while the 8087-3 is a 5Mhz chip. As for the orignal post, I tried running a 8087-3 in a turbo XT, if the machine was booted at 4.77Mhz it would run, if I changed the speed to 8Mhz after it booted or booted at 8Mhz then it would lock up. My advice is get a 8087 that matches the highest speed of the machine.
test@sparc1 (07/27/90)
johnv@metaware.metaware.com (John Vinopal) writes: >> Stuff about 8087's overheating deleted. >It is common (risky) practice to overdrive chips. There were 25Mhz 386 boxes >long before the i386-25 was released. Why then can this not be done with the >387 chips? I have heard that at least with the 287s the chips are all basically >the same but they have been verified at different clock speeds. Thus an 8Mhz >is no different than a 10Mhz, but for the fact that the 10 is guarenteed to >work at 10. Could someone expand on why a 25Mhz 387 could not be used in a >33Mhz box? If overheating is the only problem then whats the deal, install a >cooling system. > > johnv@metaware.com Chips which are rated for a specific speed are tested by driving them at differ-ent speeds; when a speed is reached where the chip no longer works reliably, it's assigned the speed at which it last functioned properly. If you run a chipfaster than its rating (which, as you say, is a common occurrence), you're prob-ably safe if you only push it a couple of Mhz. I wouldn't recommend buying a 16 Mhz 386 and trying to run it at 33 Mhz, however :-). 16 Mhz 386, and trying to run it at 33 Mhz, however :-).