Hi, I have a similar card in the PCs in my collection, the motherboard I have is a PCChips M506 V1.1 and it's a socket7. He installed a Cyrix 6X86 P166 + CPU, which goes to 133MHz, I remember he has the COAST cache module, but I should see what model it is.
As a CPU Surely you can put all those single voltage, then Pentium i200 (not MMX), Amd K5 if you find a very rare 200 or more easily a 166, Cyrix or IBM 6X86 P200 + if you can set FSB at 75 MHz or P166 + with FSB 66. Then there would also be the IDT Winchip C6, there are various models, the most common is 200MHz, but there is also a 225MHz and a 240MHz.
For the AT power supply, I would recommend an ATX-AT adapter, so could you use a cheap, good quality ATX that you might already have? The cost of the adapter is certainly cheap, while an AT power supply is probably expensive, of course you can take a look at the online auction sites.
For the possible installation of the Pentium MMX you must first understand the exact model of the MB (including the version), this information can be found by starting a program like CPU-Z or CPUID (also goes well with the P100) in the motherboard section.
But from what I remember, maybe you need a special VRM card, to support Pentium MMX, alternatively there would be the adapter for Socket5 / 7 is explained here what you can do:
http://www.thg.ru/howto/20010212/print.html

(1) is this motherboard really a PC Chips M506 or M507? Is it really a Socket 7 motherboard? Or is it actually a Socket 5? PC Chips M506/M507 is my best guess so far, but please correct me if I'm wrong. Warnings are welcome.

No idea on the PC Chips model number (did you check the PC Chips Lottery?) but it is definitely So7 as you can select 2.5x and 3x multipliers. That means the second multiplier pin (the biggest difference between So5 and So7) is supported.

(2) what is the fastest Pentium CPU supported by this motherboard? I have lost the manual, but judging from the Rainbow Software website, it seems I can use 200 MHz Pentium CPU by selecting 66 MHz CPU clockspeed (pins 1 & 2 closed on JP01, JP11 closed, JP12 open) and setting CPU internal clockspeed configuration at 3x speed (JP13 open and JP14 closed).

Yep, P200 is the fastest Pentium that can run on here unmodified.

(3) will putting a 512 KB cache on a stick (COASt) on the motherboard's SL1 slot help improve frame rate in non-accelerated, texture mapped 640x480 3D games? And where to find such COASt? Is this one compatible with my motherboard?

The board already seems to have 256kB (?) PLB onboard, unless PC Chips was up to its usual fake cache stuff. If the onboard stuff is fake, adding real cache will improve performance a lot. If it's real, upgrading 256kB to 512kB isn't going to make a massive difference, but certainly won't hurt. As for where to find... the usual places for old PC stuff, which differ from location to location, and I'm afraid any NW-European tips I could give would be utterly irrelevant in your neck of the woods.

(4) where is the best online store to find AT (instead of ATX) PSU?

Same as above. If you want new, look for the Startech PSUs, but you could also consider one of the better ATX-AT cables with an ATX PSU.

(5) Can I put Pentium MMX CPU on this board? I remember you need a voltage regulator module (VRM) to use MMX CPU on an Intel 430FX motherboard, but this board seems to have VRM connector slot (labelled as CN7 on the manual). Where could I find such VRM? Tried ebay but to no avail.

Boards with VRM connectors were all the rage around 1996 - a simple way to sell old stuff while promising an upgrade path that in reality was almost never used, as by the time your non-MMX CPU needed replacing you were probably already in Celeron/K6-2 period if not P3/Athlon and that VRM wasn't going to help you there (nor would it have been availalble). I can't recall ever having seen a VRM for a regular AT board like this. They probably do exist, but no clue as to where to find one. Not sure about BIOS support either.

I'd agree with PC@LIVE that a socket converter a la Kingston/Evergreen would be a more realistic option - but given that they tend to cost more than a whole So7 split voltage board, only go down that path if you really, really want to keep this specific motherboard.

VRMs were more common in PPRO systems, most folks end up having to build one if they want one, they were quite rare.

Best bet would be one of the overdrive sockets with its own vrm onboard

dionb wrote:

(4) where is the best online store to find AT (instead of ATX) PSU?

Same as above. If you want new, look for the Startech PSUs, but you could also consider one of the better ATX-AT cables with an ATX PSU.

Startech no longer has that model of AT PSU for sale. The only ones available through new channels now are from a very non-reputable brand, and I haven't purchased one for teardown, nor have I looked at any internal shots to know how well it's constructed. I suggest the best option is probably the used market or a new ATXv1.3 PSU from Startech with a converter cable. The ATXv1.3 PSUs provide all the required voltages, so the cable can be the basic type with no -5V regulator.

Wouldn’t an overdrive cpu run at typical P-100 voltages? I’d bet an mmx overdrive would work.

BinaryDemon wrote:

Wouldn’t an overdrive cpu run at typical P-100 voltages? I’d bet an mmx overdrive would work.

The overdrive CPUs have onboard voltage regulation. So externally, they run at the regular old Pentium Voltages, but then the onboard regulation circuit changes it to the needed voltage for the CPU.

According to webhq, it supports P55C (pentium mmx) with VRM http://www.elhvb.com/webhq/models/pcchips/m507.htm
The jumper manual archive also contains the latest bios which is from april 1997.

The cache looks definitely fake as I can (hardly though) read "WRITE BACK" on them which screams for pcchips' fake cache

I have a M520 motherboard which is based on the i430VX, has absolutely no cache (not even fake chips) and uses the same VRM connector. But I do have a VRM that fits in there, I can take pictures of it if somebody wants to reproduce it

I would like to add some info on the M506 V1.1 card I have on my PC.
I found a note on the COAST module in my PC, it's a 512KB module and it says "RAM REALTEK", has soldered 4 HY534256S-70 chips
I don't know if this info can be useful, but the suspect 256KB on-board cache is fake.
The configuration of my PC would be like this:
MB M506 + 512KB cache module
CPU CYRIX 6X86 P166 + 133MHz
PCI S3 Virge / DX 86C325 4MB Video Card
HD Conner 1620MB-CFS1621A
ISA Creative CT2770 Sound Card

I ran some time ago with some programs, including HWinfo 3.05 and these are the results:
Benchmark 122,311 Dhrystones / s
Video Throughput (text): 18.791KB / s

70ns cache?

Well don’t that beat all

Interesting posts, thank for the replies, guys. This is the first time I rebuild something older than 440BX.

While we're at it, I just remembered something; my Pentium 100 often froze during Windows 95 startup screen. I had to use the reset button, and then Windows went to safe mode on the next boot. I didn't need to make any changes, I simply restarted Windows, then it started normally on the next boot. However, it happened quite frequently that it was very bothersome. It happened after I changed the video card to Matrox Mystique (the original MGA1064SG), and it only happened after I installed the Mystique driver (didn't happen with standard VGA driver). What could be wrong?

And what does DMA configuration mean on the manual? Obviously it enables us to select between DMA 1 and DMA 3, but for what?

Selecting between DMA 1 and DMA 3, but for what purpose?

Also, this discussion implies you can simply use MMX CPU on Socket 7 and even Socket 5 motherboards without VRM (and without overdrive chip either). The only consequence is hotter CPU, so you need to use better cooling. Could anyone confirm or rebuke Crashman's implications?

Crashman wrote:

OK, something else you should know: Even if your board doesn't support adjustable voltages, or a fixed voltage below the original 3.3v, you can run a Pentium MMX on it. Yes, 3.3v is more than the rated 2.8v. No, that won't hurt the CPU. I've sold hundred of overvoltage chip systems without a single return.

OK, Intel's Pentium MMX 233 uses a 3.5x multiplier, which is duplicate of the 1.5x setting, hence if you can set your CPU at 100MHz via 66x1.5, you can stick in a Pentium 233 MMX and have it run properly (sometimes BIOS reports the wrong speed, but that's not a problem, you can check it yourself in Windows using CPU-Z).

OK, so if your board requires an adapter, I'd skip that expense and use a 233MMX. You should really tell us which BOARD you have to begin with. Lacking that, we can figure it out for you using the BIOS ID that comes up when you start the system.

Crashman wrote:

Check inside the box, the board should support 1.5x multipliers and 66MHz bus. Probably via a set of switches. It shouldn't have any problem running a Pentium 233MMX, except that it will probably tell you it's running a Pentium 100 by mistake since the BIOS isn't programed to understand what a 233MMX is. Still, it should run the 233MMX at 233MHz if you use the Pentium 100 setting of 66MHz bus and 1.5x multiplier (multiplier is probably fixed at 1.5x anyway).

And the 233MMX is like 4x faster than the Pentium 75, due to increased bus speed and MMX capability.

Because of the overvoltage, you'll want to run a heatsink with fan.

Okay, so my Pentium 100 motherboard appears to have both 1.5x multiplier and 66MHz bus. According to Crashman, I could easily put a 233Mhz Pentium MMX on the mobo sans VRM, and without overdrive chip either. The CPU will be recognized by BIOS as Pentium 100, but it will run at fully 233Mhz. It will also be hotter due to overvoltage, so I'll need better CPU cooling.

Crashman said:

You don't need an adapter to run the Pentium MMX in a Socket 5 board. Even though Socket 7 is supposed to be the dual-voltage version of Socket 5, and even though the Pentium MMX is dual-voltage (officially Socket 7), the Pentium MMX is actually a Socket 5 CPU. That is to say, the Pentium MMX lacks the added pin that would have made it Socket 7.

I've done lots of Socket 5 Pentium MMX systems. No adapter required. If you find that hard to believe, I can take a photo of the bottom of both a Pentium MMX and K6-2 to prove to you that the K6-2 has the extra pin while the Pentium MMX doesn't.

Like I said, Pentium 233MMX will run at 233MHz in a Socket 5 board using the Pentium 100 setting, because the voltage difference isn't enough to fry it, and because the 1.5x and 3.5x multiplier are the same setting. The only thing you need to concern yourself with there is that the CPU will run a little hotter than stock, so you should use a fan cooler.

Intel BIOS doesn't support K6-2's.

So, it will work on Socket 5 motherboards as well.

Are those are true? Anyone has ever tried it before?

Thats a misinformed recipe for a disaster.

1.5x is indeed rewired as 3.5 on some mmx, but other are locked, so you can set any multiplier and it'll keep the one it's made for.

As for the voltage, I believe that is kinda true, but I don't think it's harmless at all. Sure it won't be like a DX4 running on 5v instead of 3.3, but I'd still be worried with a +0.5 overvolt.

You can find vrms to buy online and you can probably also build your own.

Other than this, this board is said to support mmx chips so the proper speed should be seen in the BIOS, at least with the latest one.

If you want to put a 233 in that MB, I remembered that there is a K6-233APR with VCore 3.3V, so in practice it is a single core, the problem with those K6 CPUs is the heat they give off, including the K6-233ANR with Vcore 3.2V
I don't know if the APR and ANR are the same CPU, and therefore use any K6-233 3.2V setting it to 3.3V
The only thing I know for sure is that if you have linear voltage regulators, increasing the heat produced by the 2 Mosfets next to the battery up to 233MHz, it will be very high so as to require an additional fan that blows over fresh air.
As a suggestion, since the k6 has the multi unlocked, I would tell you to increase in frequency starting from 166MHz and see how it goes (ie how much it heats up Cpu + Mosfet), then if the temperature is OK and the PC goes well try at 200MHz, already at this frequency it should warm up enough.
We wrote about it a few days ago, the MB is another with VX chipset:
Re: K6-2 300mhz in Socket 7 motherboard?
On what Crashman says, that of Socket5 + P233MMX I never tried, and I don't doubt that it will work, I wouldn't know for how long?
My personal experience was in 1999 with an MB 430VX and a MII300 @ 233MHz, everything went well for a month or two, then the MB went into service and never came back, in return I had a VIA VPX

The P6 micro-architecture (Pentium II and Pentium III) include information that a voltage regulator IC can read to set correct power output. Before that, for the P5 (Pentium) and P6 (Pentium Pro only) CPUs where produce with different voltages and need a voltage regulator accorded to their specs to operate. They are in the form a board that can be inserted in your white connector. But for the most common voltage (typically 3.5V), motherboard already include the correct output, so it only need a bridge (the red jumpers) to pass the power to the CPU. More than that, there is a wide variety of voltage regulator board with different connectors, even with same manufacturer sometime. So finding one today.....
That said. Some motherboards accept Pentium and Pentium MMX, must most the time they aren't. So the better solution is to use a Pentium OverDrive MMX which, as it was said before, include its own voltage regulator and is able to drive the bus to set the correct frequency. So you must let the original frequency of your CPU. By example upgrading a P133 to a P200 MMX OD. You only replace the CPU and do not change anything on the motherboard. The problem is that OverDrive CPUs are rare and expensive. But they have more cache and MMX instruction set.

So to answer your questions:

Kreshna Aryaguna Nurzaman wrote:

(1) is this motherboard really a PC Chips M506 or M507? Is it really a Socket 7 motherboard? Or is it actually a Socket 5? PC Chips M506/M507 is my best guess so far, but please correct me if I'm wrong. Warnings are welcome.

If it is written Socket 7 that it should be Socket 7. The difference is an additional pin for voltage to get better stability and support higher clock rate.

Kreshna Aryaguna Nurzaman wrote:

(2) what is the fastest Pentium CPU supported by this motherboard? I have lost the manual, but judging from the Rainbow Software website, it seems I can use 200 MHz Pentium CPU by selecting 66 MHz CPU clockspeed (pins 1 & 2 closed on JP01, JP11 closed, JP12 open) and setting CPU internal clockspeed configuration at 3x speed (JP13 open and JP14 closed).

I think you are correct. P200 are set with a 66 x 3 multiplier. So in reality it is 198 MHz or the multiplier is something like 3.03 and it is almost 200 MHz.

Kreshna Aryaguna Nurzaman wrote:

(3) will putting a 512 KB cache on a stick (COASt) on the motherboard's SL1 slot help improve frame rate in non-accelerated, texture mapped 640x480 3D games? And where to find such COASt? Is this one compatible with my motherboard?

The difference between 256 and 512 KB L2 cache are not huge with video games (Build Engine, id Tech 1) but it should help to get smoother frame rate than better performance.

Kreshna Aryaguna Nurzaman wrote:

(4) where is the best online store to find AT (instead of ATX) PSU?

I don't know. Especially for good quality ones.

Kreshna Aryaguna Nurzaman wrote:

(5) Can I put Pentium MMX CPU on this board? I remember you need a voltage regulator module (VRM) to use MMX CPU on an Intel 430FX motherboard, but this board seems to have VRM connector slot (labelled as CN7 on the manual). Where could I find such VRM? Tried ebay but to no avail.

The fastest Pentium MMX OverDrive is 200 Mhz and all the Socket 7 motherboard I have seen support frequency up to that, so there is great chances it works.

Kreshna Aryaguna Nurzaman wrote:

Interesting posts, thank for the replies, guys. This is the first time I rebuild something older than 440BX.

[...]

And what does DMA configuration mean on the manual? Obviously it enables us to select between DMA 1 and DMA 3, but for what?

DMA for parallel port ECP mode. Defauly is 3. Only relevant if you set it to ECP. If you are doing serious stuff on LPT (ZIP drive, NIC, etc) you would want ECP, otherwise, just set it to standard or bi-directional so it doesn't eat that DMA you might need for other things.

Also, this discussion implies you can simply use MMX CPU on Socket 7 and even Socket 5 motherboards without VRM (and without overdrive chip either). The only consequence is hotter CPU, so you need to use better cooling. Could anyone confirm or rebuke Crashman's implications?

P55C is one of the best engineered CPU cores out there and it can take massive abuse before failure. This is an example of such abuse. Yes it can work, but it is very bad for the CPU and it might kill it. Strongly not recommended, although yes, it usually will work (for a while).

Okay, so my Pentium 100 motherboard appears to have both 1.5x multiplier and 66MHz bus. According to Crashman, I could easily put a 233Mhz Pentium MMX on the mobo sans VRM, and without overdrive chip either. The CPU will be recognized by BIOS as Pentium 100, but it will run at fully 233Mhz. It will also be hotter due to overvoltage, so I'll need better CPU cooling.

No idea what BIOS will recognize it as, but yes, the same setting as 100MHz (1.5x66) will give 3.5x66=233MHz with a P55C. It will however be significantly overvolted and run far hotter than intended. Good cooling will mitigate this, but once again, not recommended.

So, it will work on Socket 5 motherboards as well.

Are those are true? Anyone has ever tried it before?

So5 and So7 are almost identical. The biggest differences are that So7 supports two multiplier pins (for 1.5x, 2x, 2.5x and 3x) where So5 only has a single one (for 1.5x and 2x), and that So7 optionally supports split voltage - but early So7 boards rarely implement that. Given that a P233MMX recycles the 1.5x multiplier for 3.5x, it will run - at 233MHz - on an So5 board, but it will be just as badly overvolted as on So7 without 2.8V, with consequences for thermals and so also longevity. Not recommended.

dionb wrote:

So5 and So7 are almost identical. The biggest differences are that So7 supports two multiplier pins (for 1.5x, 2x, 2.5x and 3x) where So5 only has a single one (for 1.5x and 2x), and that So7 optionally supports split voltage - but early So7 boards rarely implement that. Given that a P233MMX recycles the 1.5x multiplier for 3.5x, it will run - at 233MHz - on an So5 board, but it will be just as badly overvolted as on So7 without 2.8V, with consequences for thermals and so also longevity. Not recommended.

Indeed. I have seen an old Socket 7 motherboard having this voltage problem with an overheating CPU, an ECS board if I remember correctly.

On this site I found some important info on the K6-233 with Vcore 3.2V or 3.3V:
http://www.amd-k6.com/cpu-specs/
What matters is the Watts, because the linear regulators warm up proportionately.
In practice taking as an example the K6-233 (VCore 3.3V) and a K6-233 for laptop (VCore 2.1V), we note that the maximum Watts drop from over 30 to 9 and consequently the VRM should give off little heat.
So if it is not possible to have a Dual-Voltage VRM, I do not recommend for the K6 frequencies above 200MHz because the higher Watt demand, over time can create problems for the MB (also taking care of and improving the cooling).
I remember that there are CPUs like the IDT Winchip C6 that reach 240MHz, they are CPUs with a lower consumption, so they might not create problems, at the limit the old BIOS recognize them at startup mistakenly as 80486DX66, but if it starts it should work.
Of course using a CPU adapter with VRM on board (like evergreen or upgradeware), you can install a K6-2-400 or even a K6-3-400, setting FSB 66 and multi 2X (which the CXT interprets as 6X).
In the PCs of my collection in MB SKT7 with single voltage, in one I have on an Intel Pentium classic i200 (200MHz), and in another one Pentium Overdrive 166MMX (which has the dual voltage VRM integrated in the CPU), I also have various CPUs which I tried like the AMD K5-166 and the IDT Winchip C6 200.

I found this web page dedicated to the M506 / M507, here you can find a lot of info, on CPU cache and more.
I think it may help you to update your MB.
http://th2chips.freeservers.com/m507/index.html

Oh nice a bios from 1998 ^^