MTech R581-A SiS 5591 Socket-7 Board

-AGP R581-A itself, what forced this review to continue on to The Bad was the publicity that the motherboard received before its release, the consensus being that the R581-A fully supported the 90/100MHz bus speeds.  Hype will surround just about any product's release, what made the R581-A's release even worse was that vendors were selling the motherboard as being the first official 100MHz bus speed Socket-7 AGP motherboard, which is very wrong. 

The R581-A will boot at the 100MHz setting, however unless you use your computer to watch the memory counter you'll receive a bit of a disappointment from the R581-A.  In theory, you shouldn't be disappointed by the erratic behavior of the motherboard at the 100MHz bus speed setting, however because just about everyone that sells the motherboard calls it a 100MHz Socket-7 motherboard you will naturally be disappointed to find out that your new purchase isn't filling the shoes you imagined it would.  Why doesn't the R581-A work at the 100MHz bus speed?  Three reasons:

1) RAM - although this is probably the factor that makes the least difference, if you don't have PC100 SDRAM, there is no guarantee that your memory will work at the 100MHz bus frequency.  However if you do have PC100 (Revision 1.0) SDRAM, then you can rest assured that any problems you have at the 100MHz bus frequency are due to components other than your RAM.  Which leads us to the next reason...

2) CPU - here's something most people overlook, running your K6 at 100 x 2.0 and 66 x 3.0 both yield a clock rate of 200MHz...but why is it that we can obtain benchmarks of the K6 at 66 x 3.0 much easier than the K6 at 100 x 2.0?  Well, think of it this way, if you increase the bus speed of your memory above the recommended specification you're going to have excessive amounts of noise in the signals which traverse that bus...more specifically, signals coming from and going to your processor.  If you have too much noise in your signal, then your processor will start receiving signals that are difficult to interpret, this is where the processors that are manufactured with quality in mind separate from those that are designed only to run at the speed they are rated at...and not one megahert more.

3) L2 Cache - this is the biggie.  The L2 cache on the R581-A takes the biggest hit when running at the 100MHz bus speed, the 8ns Tag RAM used on all current R581-A motherboards is able to keep up with the 90MHz bus speed, which is why clocking the Pentium MMX using a 90MHz bus speed works flawlessly, however the Tag RAM is simply too slow to function at the 100MHz bus speed.  In theory, a 6ns Tag RAM is required for operation at 100MHz...if this does end up being the one cause (which is very unlikely) for the instability at the 100MHz setting then you can expect a revised R581-A to be released in the near future...sporting a 6ns Tag RAM.

The above is definitely not the fault of MTech, but the media in general (this site included).  It must be made clear now that the R581-A should be considered a great motherboard because of its performance, stability, and quality, not because it features a bus speed setting the competition has yet to produce...we all remember the last time that happened with a motherboard...

If you do decide to experiment with the R581-A's 100MHz bus speed setting do so at your own risk, the Western Digital Caviar drive used in the R581-A tests died after some experimentation with the 90/100MHz bus speeds...just one of the unfortunate casualties of overclocking.

As mentioned before, not all CPU's will work at the 90MHz bus speed setting, the Pentium MMX had no problems at all clocking in at 180/90, 225/90, and 270/90.  The AMD K6 and Cyrix 6x86MX test systems kept on corrupting the Windows Registry file, however with extreme and unorthodox cooling methods Winstone 97 did complete a single test run, revealing the performance of the 90MHz bus speed on Socket-7 processors is quite dramatic itself...whetting our appetites for an impressive introduction of the first true 100MHz bus speed Socket-7 motherboards later this quarter.

 

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IRQ Usage

• Allows user to individually set IRQs for each Legacy ISA card

• Allows user to Assign IRQ for Modem

 

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BIOS Settings