ASUS P4B533 - Workaround to set 3:4 CPU/Memory Ratio Above 133 MHz

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Like it says – Dinglehoser, aka Susuk Lim

I have found a way to get a 3:4 CPU/Memory frequency ratio at above 133 MHz FSB on the ASUS P4B533 series motherboard. Like the P4B266 series preceding it, the P4B533 has the curious “feature” of disabling the 3:4 ratio at any FSB above 132 MHz and replacing it with a nearly useless 4:3.

There is a somewhat inelegant hack floating about the ‘net to rectify the problem on the P4B266 via a bit of BIOS trickery, but it doesn’t work on the P4B533 (in my experience, at least). With the P4B266 hack, you can’t have your cake and eat it too – memory timing is locked at 2.5-3-3-7, and any change to the BIOS, however minor, causes the ratio to revert back to 1:1.

The workaround I’ve discovered (I’m assuming this is new information, being as I haven’t seen anyone else talk about it) does not have these limitations. I have no idea if it works for the P4B266, or if it even works with other P4B533 BIOS revisions; I only know that it works for my setup.

First, the important info. I’m running a P4 1.8A at 2.7/150/1.65V, with
Corsair XMS3200 512 MB running at 200 MHz (DDR400). Timings are tCAS=2,
tRCD=2, tRP=3, and tRAS=6; voltage is set at the board’s default of 2.6V. I have a P4B533-E running the 1007 beta 11 BIOS (this workaround works for
1004 and 1007b9, the only other ones I’ve tested).


  1. Power down (obviously) and set the DIP switches to 100 MHz and whatever multiplier corresponds to your processor. Do NOT change the jumper to jumpered mode – leave it on jumperfree.

  2. Power up and select 70/35 for the AGP/PCI frequency, and 1:1 for the CPU:Memory ratio. Select any FSB above 132 MHz and an appropriate memory timing, and the actual ratio will be 3:4 at the timing you selected.

Setting the memory to 4:3 will cause the memory to run at 1:1; setting it
to 1:1 will make it run at 3:4. Strange, but it works. Attached are a
couple of Sandra screenshots.

There are a couple of bothersome quirks, however:

  1. When running any memory frequency above 166, tRP=2 or tRAS=5 will prevent the board from posting regardless of VMem setting.
  2. VMem = 2.9V prevents board from posting.

  3. VMem = 2.7V provides less overclocking potential than the default of 2.6V.

All in all, however, these annoyances are pretty minimal, as tRP and tRAS
have little if any impact on performance, and this board clocks both the
processor and memory higher at default voltage than any other 845D/845E
board I’ve encountered, even when the voltage is maxed out. (On a Gigabyte 8IRXP, the same processor could only do 2520 MHz/140 MHz/1.850V; the memory could only manage 183 MHz at 2.9V.)

With this little workaround, I think I’ve finally found the perfect P4 board in the ASUS P4B533-E.



Dinglehoser, aka Susuk Lim

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