UT85C501 chipset (alias MMXPRO, alias VXPRO-II, alias UT801x...)

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VXPro-II chipset

What I found about this exotic socket 7 chipset...

The UT85C501 has some disadvantages:

A further weak point is: NetBSD and older Linux versions (kernel 2.4) have no PCI-bridge driver for this chipset. With exception of a VGA card you can't use any other PCI-slots (no PCI devices are found).

OpenBSD and newer Linux versions (tested with Slackware 14.2) have no problems.

Some additional stuff:

PcChips M558, M559 and M592

The three motherboards are very similar.
I own two versions of M558. On the first one the chipset is labeled as "MMXPRO" (produced end of 1997). The second one is marked as revision 3.0 (produced begin of 1998) with the more common chipset label VXPRO-II:

M558 with MMXPRO labeled chipset M558 with VXPRO-II labeled chipset

The M559 has a CMI8330A ISA sound chip on board (was relabeled by PcChips as HT1869V+), 512kB single chip cache and two additional DIMM sockets (for 5V modules only):

M559

M592 has also CMI8330A ISA sound plus SiS6215 graphic chip (1MB Video-RAM, optional 2MB) on board, only two PS/2 SIMM sockets (but with 16MB RAM already mounted on the board) and one 168 pins DIMM socket for 3.3 or 5V FPM / EDO modules:

M592

Benchmark in comparison to PcChips M537 and PcChips M558

The M537 is the "sister" board of the M558 but it uses the VIA VT82C580VPX with USB1, Ultra-DMA33 and 3.3V SDRAM support. Both boards were produced nearly at the same time (end of 1997) so they are well suited for comparison. I used an AMD K6-233 processor (clocked with 66MHz x 3) which is a suitable processor (date code 1997) for both motherboards... The exact setup is documented in this LibreOffice spread sheet. If you startup both motherboards the M537 feels much faster than the M558...

First we tested the IDE-interface. The result here should be clear because of the missing Ultra-DMA mode in the UTron chipset. It achieves only one third of the performance of the VIA chipset during the write test and a half of the performance during the read test:

IDE performance M537 / M558

But also the cache / memory interface was not state of the art:

Memory performance M537 / M558

Now we understand the bad reputation of the VXPro-II chipset boards. They have only one more thing left: the most exotic chipset of all socket 7 boards... :o)

A little bit tuning on M558

My M558 boards were only equipped with 256kB cache and 8kB tag-RAM. 64MB RAM can be cached with this size but the maximum capability of the M558 is 128MB.

Two additional cache chips can be mounted on the motherboard but this is only a task for advanced electronic hobbyists:

  1. Remove the old tag-RAM chip, which was a UTron UT6164JC-15 (8KBytes x 8) in my case. It is much easier if you temporarily remove the electrolytic capacitor which is place between tag-RAM and edge of the board.
  2. Place a tag-RAM with 32kBytes x 8 and 5V power supply in a SOJ28 package. I used an ISSI IS61C256AH-12J here which still was available on ebay in 2019.
  3. If you have a wired jumper as cache size selector: removed it and place a three pins jumper instead.
  4. Place two additional cache chips: you need 32kBytes x 32 chips with 3.3V power supply in a 100 pins QFP package. I used here ISSI again: IS61C632A-7TQ (bought also on ebay).

Now we have 512kBytes cache for 128MB RAM:

M558 with 512kB cache.


falk.richter*at*yandex.com
Last update: February 17, 2020