Very interesting. I would consider doing this to my K6XV3+/66, but I suspect that board has severe aging issues, so at this point I don't feel like investing into a board that may die any day...

Limiting factor are the crappy green electrolytics in the VRM circuitry around the CPU socket. So I would recommend a recap before going any further.

I forgot to mention the cacheable areas:

"Write Through"
512K -> 128MB RAM
1024K -> 256MB RAM
2048K -> 512MB RAM

"Write Back"
512K -> 64MB RAM
1024K -> 128MB RAM
2048K -> 256MB RAM

majestyk wrote on 2022-11-16, 08:47:

Limiting factor are the crappy green electrolytics in the VRM circuitry around the CPU socket. So I would recommend a recap before going any further.

This is most likely what I will do when it starts crashing too frequently.

IIRC, if your installed RAM is larger than the cacheable areas, and you don't have a 2+/3+ CPU (with internal cache), then you will experience performance drops, correct? Can stability suffer as well?

Depending on the OS and it´s memory usage there will be performance drops. Stability will not be affected.

I should also add that if you are using a "K6 plus" CPU onboard (then) L3 cache becomes an issue of lower importance that doesn´t play a major role in performance.

Don´t wait too long with a recap. Fading electrolytics cause higher ripple on the supply voltages and can stress the chips.

I found one of my old K6BV3+ /66 the other day that was equipped with just one 1MB cache chip.
I always wanted to upgrade to 2MB but some component was always missing.

The first step is to solder a second 64x128K chip in it´s place.

The second step is to adjust the jumpering. R145 has to be moved to position R143 and R 137 (or R138) to position R203.

The third step is replacing the TAG RAM:
On 512K or 1MB versions there is a 256K chip (32Kx8, 28 pin SOJ 300 MIL) while 2MB boards have a 512K chip (64Kx8, 32 pin SOJ 300MIL). All chips are 8nS.
These 512K chips were made bei Utron and one more manufacturer and are virtually non-existent today. You will find datasheets but no seller offering them.
That´s why I chose a 1MB chip (128Kx8) 10nS hoping a good sample of a 10nS type today might be as good/fast as a bad sample of a 8nS type back in 1999.
These chips are still available, but you have to make sure they´re 300MIL SOJ and that they have the old pinout with Vss and Vcc at pins 32/16. Modern chips have these pins in the middle of the package due to advantages at high frequencies.
Of course there´s one unused address line in the 1MB chip (A16). This line needs to be grounded, the system won´t work with this pin open. There´s a ground pad nearby so this is no effort.

I still have to test this setup to make sure there are no instabilities at 100MHz FSB.

The FIC VA-503+ has 1MB L2 cache and two 512K chips. The TAG RAM is 256K and the layout only provides the 28 landings for this chip.
I have repeatedly read in online boards that there is a "rare 2MB version" of this model. I doubt this ever exixted due to the TAG limitation.

I tested this setup with both 256MB and 512MB RAM:
In the 256MB case all 256MB are being cached in "Write Back" mode, "Write Allocation" gets enabled by BIOS.

If there´s 512MB RAM present, 512Mb are being cached, but BIOS switches to "Write Through" mode to avoid half of the RAM being uncached. Write Allocation is disabled in this case.
Th data from the table of cacheable areas (see above) is correct as we see.

And here´s a picture of the finished product:

It seems that Utsouce has all available needed for the 2mb cache upgrade:

https://www.utsource.net/en/sch/ut61512jc-8.html
https://www.utsource.net/en/sch/lp61l64128f-4.html

majestyk wrote on 2022-11-16, 08:40:

The DFI K6XV3+/66 is a great socket 7 mainboard and I used it in one of my office PCs for years. For no obvious reasons most of the sold mainboards of this model had 512K onboard cache, a few had 2MB (unlike the baby-ATX version that came with 1MB or 2MB more often).

Seems I have one of the "rare" (?) in-between variants, with 1MB (using one LP61L64128F-4 chip, with the second socket empty). If I understood this thread, it seems that it is not worth it to attempt to upgrade the cache to 2MB, given that the system currently runs with a K6/2+ CPU and 256MB of RAM.

According to this article Windows benchmarks gain about 11% profit from 2MB vs 0MB, while there's no difference for 3D gaming:

https://www.anandtech.com/show/211/3

dr_st wrote on 2023-07-14, 19:58:

... If I understood this thread, it seems that it is not worth it to attempt to upgrade the cache to 2MB, given that the system currently runs with a K6/2+ CPU and 256MB of RAM.

As long as you are using 256MB RAM, 2MB won´t make a difference - when you´re running a "non-plus" CPU, because 1MB L2 cache is sufficient for caching 256MB.

Note that Anand doesn´t say a word about the RAM size used for the tests.

I've got an update on getting the required chips. The super rare UT61512JC-8 was not available on Utsource. I googled a bit and found this source:
https://www.wlschip.com/ut61512jc-8-p0719001p1.html

I ordered 12 pieces there and they arrived today:

When having a look at the label printed on the antistatic bag you'll also get this source:
https://www.sic-chip.com/products/ut61512jc-8-719001

Wlschip asked $5 per chip, $40 shipping costs with FedEx (took 5 days from China to Germany) and $6 PayPal fees. FedEx additionally charged EUR 16,60 customs. Altogether this was not cheap, but we have an existing source.

Thanks for sharing this source!
I think I´ll order a couple just to be prepared for future upgrade projects.

Glad I came across this thread.. been wanting to do this mod for a long time.

Going to order everything to upgrade 2 of my super 7s

Epox EP-MVP3G2 to G5 (Currently 1MB Upgrade to 2MB with TAG)
DFI K6XV3+/66 (Currently 1MB, Upgrade to 2MB with TAG)

Haven’t had much luck finding the EliteMT 64128 chips so far..

I'm a little confused about the comment on this page:
https://theretroweb.com/motherboards/s/dfi-k6xv3-66-rev.-b
Board is not 2MB L2 capable since it does not support the 64K x 8bit (SOJ-32) SRAM for the necessary TAG addresses.

Is all this is saying that you cannot simply upgrade the cache chips, and also need to upgrade the TAG SRAM chip?
Or is there something in Rev. B+ that makes it incompatible with the upgraded TAG chips? (what can it possibly be)

Both B1 and B2 versions provide the additional 4 landings for SOJ32 TAG chips.
As soon as you upgrade L2 cache for 2MB the TAG chip nedds to be replaced ba a 64K x 8 or 128K x 8 SOJ32 chip (10 or better 8nS).

@majestyk
Great thread. I have one DFI K6XV3+/66 which does not boot with L2 enabled. Will look into it with this information.