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486 processor, runs the same software and otherwise behaves just like a 486, but it runs at four times the speed of the motherboard. (The 486SX and 486DX ran at the same speed as the motherboard; the 486SX2 and X2 ran at double
that speed, and despite the name the IntelDX4 and Am486DX4 run at three times the speed of the motherboard.
The Pentium processor runs at one to three times the motherboard speed, depending on the model.)
Kingston has adapted the Am5x86 to existing 486 systems with a special adapter that runs the chip at the 3.45 volts it needs (instead of the usual 5 volts) and a cooling fan glued to the top to keep the chip cool.
Installing the TurboChip 133 varies depending on your computer but isn't hard to do. Basically all you do is unplug the old 486 chip and plug in the TurboChip, and when you turn on the computer it'll run a lot
faster. (If your motherboard runs at 40 or 50 MHz you'll need to lower the speed to 33 MHz, since the Am5x86 isn't designed to run faster than that. For that matter, if youhave a 20 or 25 MHz motherboard you may be able to
increase its speed to 33 MHz to get the best performance from the new processor.) In some cases there may be a jumper to be changed to use a 486DX processor instead of a 486SX, but I found that the TurboChip often works fine
with the "wrong" setting. It even works in older 486SX systems that had a second socket for an Intel OverDrive processor; in such a system plugging the TurboChip 133 into the second socket turns off the 486SX that's already
installed. Kingston's manual explains this well, though they don't recommend changing any jumpers; be sure to read the manual for your system carefully before making any such changes, since there may be several other parameters
(refresh rates, ISA bus speed and so on) that would need to be changed as well.
The TurboChip 133 is compatible with most 486 desktop systems, but in a few cases the chip may not work because the BIOS isn't
written to handle it properly. AMD says that one common problem is with a BIOS that mis-identifies the chip as being a Cyrix product and uses settings that don't allow the Am5x86 to work properly; usually these BIOSes will
display a start-up message that mentions Cyrix when the TurboChip 133 is installed. I tried the TurboChip 133 on four 486 systems and found that it did not work at all on one, but that one was originally designed to use the IBM
Blue Lightning processor (co-developed by Cyrix) so it may not have been intended to use any other 486-class processors.
The other three systems I tried, all designed to use the Intel 486, worked quite well
with the TurboChip 133; the folks at Kingston were worried that some of them may have been incompatible, but I had no problems in any of them. As expected I got the best results in the newest of the three systems, which runs
the processor
at a full 133 MHz. I used Technical Pixies' WindSock benchmark utility, which emulates Intel's iCOMP 1.0 performance index, and got a result on that system of 616 – slightly higher than the value of 610 that
Intel quoted for the 75 MHz Pentium processor, and comfortably faster than the 83 MHz Pentium OverDrive that
goes in newer 486 systems. On my own 486 system, which has an older BIOS, the value I got was a bit slower (but
still nothing to sneeze at) at 574. Part of the Am5x86's performance boost comes from its use of 16K of internal cache memory; the original Intel 486 had 8K, so many systems' BIOSes are written to use only that much and won't
get every last ounce of the Am5x86's performance. While it's possible that newer applications won't run as fast with the TurboChip 133 as they would on a 75 MHz Pentium processor – since they may be optimized for the Pentium,
and the Kingston product is a 486-class chip – I'd expect performance to be more than adequate for any normal computing tasks.
The TurboChip 133 is best suited to the many major-brand 486 systems that use
proprietary case designs and won't accept an upgrade motherboard – and particularly for those that won't take the Pentium OverDrive.. If you have an industry-standard machine (especially if it uses 72-pin SIMMs that you could
keep) you may do well to upgrade to a new motherboard that will take a 100 MHz, 133 MHz or faster Pentium processor, though this may require new video and/or I/O cards as well, but if that sort of upgrade is beyond your budget
the Kingston TurboChip 133 is something to consider.
-- Ed Ellers
Link to Kingston Technologies Web Page
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