The first time that we all heard of 75 MHz bus speed was, when the
Shortly after the announcement from Cyrix about the 75 MHz bus, boards with the
I know for sure now that the Asus P/I-P55T2P4 even supports 83 MHz bus speed !!! Markus Sundstrøm was so nice to share this little secret with me. It's the following jumper setting: JP8 1-2, JP9 1-2 and JP10 2-3. 83 MHz bus speed means 41.5 MHz PCI clock, and the following CPU speeds: 125 MHz, 166 MHz, 208 MHz and 250 MHz. However do I have my doubts that FPM or EDO RAM will be able to put up with this speed. IMHO 83 MHz bus speed will be reserved for SDRAM, which unfortunately isn't supported by the HX chipset.
Here the comment of two visitors, who've been using the Asus P/I-P55T2P4 successfully at 83 MHz bus speed with EDO:
Thought you would like to hear about the 83MHz bus speed on the Asus P/I-P55T2P4. I had thought it wasn't possible without instability, but after hearing of a friend's success I tried it. I am running a B-step P133 at 83MHz x 2.0, with 2 8x32 60ns micron EDO, and have yet to experience any sort of crash, even in win95. Guess SDRAM is not a requirement. My memory speed is set on 60ns in the system BIOS. If you'd like I can post quake, ctcm or whatever benchmarks you like. My overclocked system is a good bit faster than a true p166.
Hello, I would also like to tell you that I have successfully overclocked by P-133 using an 83Mhz BUS speed, from a 133Mhz to 166Mhz without any problems at all. In fact, the chip runs cool and the heatsink doesn't even get warm. I am using plain old OKIDATA 60ns EDO RAM (nothing expensive like Micron). I can use the 60ns RAM setting on my P55T2P4 board and everything is completely 100% stable in Win95 and DOS. Interesting though, is that I had to change my CPU voltage from Standard to VRE to get this to work successfully. When it was at Standard, my Windows 95 would get wierd errors occasionally even at 75Mhz BUS, and it wouldn't even run any programs at 83Mhz BUS. But when I put it to VRE to give it a little bit extra voltage, everything runs 100% at all the BUS Speeds.
It looks like both my SC-200 SCSI card and Matrox Millennium both agree with the 83Mhz bus speed because I have never had a problem. I have heard bad things about the Adaptec 2940UW card though, like the older revisions don't even work with 75Mhz, and you would be VERY lucky to get one running on 83Mhz BUS speed.
Just thought I'd let you know.
Sounds like this is the way to go. I've been ordering one of these boards myself and can't wait to run my CPU at 208 MHz (2.5 * 83 MHz).
Now as already said, running a 430VX or HX board at 75 MHZ bus speed or more is something which isn't supported officially, and that is why no motherboard manufacturer ever would announce the support of this bus speed. The reason for this seems fairly simple, they probably don't want to get in trouble with giant Intel, because after all does Intel not even have one Pentium CPU, which officially would run at 75 MHz bus speed and neither do their chipsets. Hence an announcement of a motherboard manufacturer, which says that their boards support 75 MHz bus speed, would be something like an invitation to overclock Pentium CPUs - something that Intel certainly won't appreciate.
There are some more things to consider, if you would like to run your motherboard at 75 MHz bus speed. In this case you'll certainly have to overclock your Pentium CPU and just as well you are overclocking your Intel chipset. This is of course invalid, if you should be using a Cyrix 6x86 P200+ and/or a VIA 580/590VP chipset. However in both cases you are also running your PCI bus at busclck/2 = 37.5 MHz. This certainly is a nice thing, as long as your PCI devices are able to put up with it. The new PCI 2.1 specifications anyway define the PCI bus to be able to work at up to 66 MHZ.
Another problem is your main memory. Will it be able to put up with 75 MHz? It most certainly will run just fine, in case you are using
Hence for most of the users, there are these things to be considered:
- you are overclocking your (Pentium) CPU
- you are overclocking you (Intel) chipset
- you are overclocking your PCI devices
- you might overclock your RAM
I'd say that for us overclockers (the typical visitor of my site :)) this is sounding just great - three dimensional overclocking in one go - let's go for it!
But don't forget:
You are overclocking your system at your own risk!!! I'm not responsible for any damage, that might be caused by using 75 MHz bus clock at your system.
Now what are the benefits? Well, there are even 3 of them.
- Your CPU runs faster than before.
- Your memory performance has increased by 12.5 %, that's more than switching from 60 to 66 MHz!
- Your PCI (video) performance increases too.
The best benchmark to show how much you are actually gaining by switching to 75 MHz bus speed is the
Does my board support 75 MHz ?
I got a very interesting mail from Jason Langhoff concerning this question. I think, it's best, to just put it up here:
There is a way you can tell if your motherboard can run at 75 MHZ. If the clock generator has either of the following brands, it is overclockable. The two brands are PLL52C59-14 and PLL52C61-01/21. If you are unfortunate enough to have ICS9159-14, it can't be overclocked (this includes me).
I'm not completely sure about the following:
The jumper settings for the PLL52C59-14 are DS3-OFF, DS4-OFF, and DS7-ON.
The jumper settings for the PLL52C61-01/21 are DS3-ON, DS4-OFF, and DS7-OFF.
If you already know this, no loss, but if not it should be able to help others find out if they can overclock their MB to 75MHZ. I do plan on getting a different motherboard, if I can successfully overclock it, so all might not be lost. I enjoy your page and think you do a great job. Thanks for your time.