cjdb@sphinx.uchicago.edu (Charles Blair) (02/13/88)
I have a "vintage" IBM PC/AT with a 6 MHz clock that I would like to upgrade to 8 MHz. What's the best chip to buy for this, and are there potential problems? (Also, what's the approximate cost?) Thanks in advance. -- Bitnet: lib.cb@uchicago.bitnet Internet: lib.cb@chip.uchicago.edu uucp: ..!ihnp4!gargoyle!sphinx!cjdb
tr@wind.bellcore.com (tom reingold) (02/14/88)
In article <3415@sphinx.uchicago.edu> cjdb@sphinx.uchicago.edu (Charles Blair) writes: $ I have a "vintage" IBM PC/AT with a 6 MHz clock that I would like to $ upgrade to 8 MHz. What's the best chip to buy for this, and are there $ potential problems? (Also, what's the approximate cost?) The reason people started changing them to 8 MHz is that they noticed that the AT was built to a tolerance that would allow that speed. You don't have to change the chip. You just have to buy a crystal. It should cost you about $5. Tom Reingold INTERNET: tr@bellcore.bellcore.com Bell Communications Research UUCP: rutgers!bellcore!tr 435 South St room 2L350 SOUNDNET: (201) 829-4622 [work] Morristown, NJ 07960 (201) 287-2345 [home]
madd@bu-cs.BU.EDU (Jim Frost) (02/15/88)
In article <5471@bellcore.bellcore.com> tr@wind.UUCP (tom reingold) writes: >In article <3415@sphinx.uchicago.edu> cjdb@sphinx.uchicago.edu >(Charles Blair) writes: >$ I have a "vintage" IBM PC/AT with a 6 MHz clock that I would like to >$ upgrade to 8 MHz. What's the best chip to buy for this, and are there >$ potential problems? (Also, what's the approximate cost?) > >You don't have to change the chip. You just have to buy a >crystal. It should cost you about $5. Alternatively there are several packages that let you do this. We use one called "AT TurboSwitch", which was advertised in Byte last summer and was reviewed by PC Magazine some time ago. I believe it cost around $50, but has many advantages over using a different crystal. More on that later. The thing is a small plate with a twist knob and a toggle switch with some circuitry on the other side (you can guess what the circuitry is so I won't elaborate). The toggle switch is used for putting the PC in 6Mhz mode for normal operation. The knob sets higher speeds, up to 12 Mhz, in .5 MHz increments. You just run your AT and keep raising the speed until the machine stops working. Our true blue AT runs at 9.5 Mhz but has problems (probably board related -- our system is "interesting" to say the very least) at 10. You mount the switch on the back of the AT. The company did a real good job designing this -- there is a small plate on the back of true blue ATs (above the keyboard port) that apparently serves no purpose. This device mounts on that and looks as if it came with the AT. The only problem is that you will not be able to put the plastic back cover back on because there is no hole in it. We just threw the cover away; it was pretty useless to begin with. After installing the switch, you run some wires and you're done. Very simple; takes about 10 minutes including pulling the cover off and putting it back on. The documentation is good enough to allow anyone who can open their PC and play with the cards to install this device. In some places it's a bit skimpy but it's followable. The documentation covers different problem cases (like 80287 problems) and goes off on tangents describing how to handle them. In actual use, the product works as advertised. You can even switch speeds during operation without a reboot, something of a boon. You'll probably never do that; you get accustomed to watching your AT fly at 9.5MHz or more. Now normal machines are painfully slow. I'd recommend this product over manually replacing the crystal because it provides you with the ability to change speed on the fly, to run your machine at its absolute peak speed, and some assurance that the enhancement will actually work with your particular AT. I'm sorry that I don't have more information on the company that makes this product -- the machine is 150 miles away right now -- but I believe the company's name is something like "Personal Computer Enhancements" or "Micro Computer Enhancements". You can probably find out by poking around in any reasonable IBM PC related magazine. Obviously there are possible problems with this setup. Some cards for the AT won't work correctly at 8MHz (or more). This is almost never a problem so I wouldn't stay awake worrying about it. Some software can have timing problems. Again, not usually a problem. Since the product is switchable back to 6MHz, software problems are solvable by the flick of a switch. Hardware problems are more of a hassle. To give you a feel for how well this product works with a variety of boards, here's our system configuration: IBM PC/AT 512k (ugly piggybacked 64kbit chips) EGA Expansion chassis with 6 processor cards and serial/parallel Standard AT drive controller 8" floppy drive controller (backwards compatibility) 2 processor cards (only 7 slots in the expansion chassis :-) I was surprised that the expansion chassis worked at the boosted speed, but there was no problem at all. I can't comment on whether or not this enhancement will work on clones. For technophiles that wonder what you can do with a PC with 9 CPUs and 8.5Mb storage, the answer is "anything you want." jim frost madd@bu-it.bu.edu