I have a problem with my internal cache. When it is activated in the CMOS setup, I get error messages when I try to start Windows. My computer is a Pentium 100 with 16Mb RAM. My problem started when I changed the jumper settings from 50MHz bus speed with a multiplier of 2, to 66MHz bus speed with a multiplier of 1.5, which is what a Pentium 100 should be running at.
But the weird thing is that when I take out one of my RAM SIMMs and replace it with a different type, everything works. Well, not quite -- I still get GPFs in Windows, but basically it works. The problem is getting rather annoying because there is a noticeable loss of performance. Any help would be appreciated.
- Ben Rautenberg
Firstly, GPF errors in Windows can be caused by a wide variety of problems. Often they can indicate faulty RAM or faulty caches. Even though your computer is booting up with different RAM installed, you may be having the same problem with the cache as before.
There are a number of variants on the Pentium 100 processor, but there are two basic types. All have a core speed of 100MHz. Some support a bus speed of 66MHz. Others can support a bus speed of either 50MHz or 66MHz and were created to work with cheaper, slower motherboards. Any Pentium 100 processor that can operate on a motherboard with a clock speed of 50MHz should be able to work on a motherboard with a clock speed of 66MHz. The 66MHz clock speed is preferable not only because it is a little bit faster, but because the PCI I/O bus runs at 33MHz. Because 33MHz is exactly half of 66MHz, it is easier to coordinate the PCI I/O bus to this speed than 50MHz. A motherboard with a clock speed of 50MHz will exhibit slower performance for PCI video cards and the hard disk controller.
If 66MHz is the ideal, why did your computer?s manufacturer set the motherboard clock speed to 50MHz? There are two likely reasons. First, they tried 66MHz and it didn?t work because of some flaw in the motherboard, but they found that 50MHz did work. (Of course, as a buyer you would be completely unaware of whether your motherboard is running at 50MHz or 66MHz, though it should have been priced accordingly.) Second, you need to have at least 60ns RAM, otherwise it may not work with the higher clock speed. Possibly the manufacturers found they could shave a few dollars off the price by using 70ns RAM, but had to set a lower motherboard clock speed to compensate.
So what should you do? You could restore your old settings. This will give you the best performance with your current hardware. If you can determine what speed your RAM is, then you should be able to work out whether you need to replace it. Your last resort may be to purchase a new motherboard. However, buy from someone who will refund your money if the new motherboard does not do the trick.
- Roy Chambers
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Category: Hardware
Issue: Sep 1997
Pages: 158
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Bus speeds and multipliers