My last issue is about performances... Doom is so slow on DOS (probably 12-15 FPS MAX) but plays perfectly on Doom95. Even DOS Quake runs better... Probably due to the CPU architecture.

Since Cyrix CPUs have much better integer than floating point performance (compared to a similarly clocked Pentium) it's very unlikely that Doom (that uses integer math) performs worse than Quake (that uses floating point math) because of CPU architecture.
It's more likely that the Doom performance problem is related to the integrated VGA. Some VGA implementations do not like the planar/unchained Mode Y that Doom uses.
You should try FastDoom to determine if the problem is Mode Y or not. FDoom.exe uses Mode Y but FDoom13h.exe uses the more traditional Mode 13h so you can compare the performance of the 2 different modes.
https://github.com/viti95/FastDoom/releases
FastDoom. A new Doom port for DOS, optimized to be as fast as possible for 386/486 personal computers!

Cyrix MediaGX SoC doesn't perform well under VGA mode Y/X, specially when lot's of OUT instructions are sent. FastDoom fixes this issue on modes 13h and VBE2. Also you can try other DOOM ports such as MBF (Marine's best friend) which also include support for additional video modes. Other option is to add an external PCI video card, bypassing the flawed one.

Edit: small video of my MediaGX (300MHz) comparing mode Y against mode 13h https://www.youtube.com/watch?v=3PAfvDsmzVY

Thanks for your help! Problem solved for Doom but I'm desperate for Dune. Any ideas?

A warning, please note to anyone reading this that these systems often use sockets that look like standard socket but they are wired completely different they may even say socket three? or socket seven on them but they are not. do not attempt to put a normal CPU in them it could fry everything.

Cool setup 😀
As for the riser,
If you can find a comprehensive pinout or a user that has one, it might be possible to replicate it it and order the pcb

This is something I’ve wondered about is the timeline
Of the different packages and types of MediaGX chips vrs the corresponding cpu socket and release dates.

I strongly remember “MediaGX” talk before the official 97 release date back in 1996 and vaguely remember prototypes being evaluated at that time. I did discuss the chip in newsgroups prior to its release.
Later My Highschool had Compaq MediaGX/180s in the library internet lab which was my first reliable/ fast internet experience.

Most of my magazines and other bs from that time were tossed and I can find no run up discussion of the MediaGX before it’s release date which I find disappointing since I followed Cyrix quite closely mid to late 90’s

I am curious when the changeover to a pseudo socket 7 happened as it must have been early
And curious when Cyrix started sampling MediaGX engineering samples.

An example of a "popular" MediaGX based system is the Compaq Presario 2200 . Looking up its history might help answer some questions. IMHO, running the stock Windows 95 install that it came with was borderline masochism, even by 1997/1998 standards .

MediaGX had decent SB16 compatibility, AFAICR, but had lackluster legacy VGA performance and borderline CPU performance . People were attracted by the low price, but "low" was an accurate qualifier for pretty much everything that thing had to offer . IMHO, MediaGX was a desperate attempt to milk the 486-compatible clone cash cow to the very last drop by integrating as much support logic as possible into the design to keep costs low while branding the thing as a valid "next generation" option . Again IMHO, getting a used high-end 486 would have been a better, cheaper and more flexible choice for pretty much any use case . The sole exception to this might have been the institutional thin client market, where cost trumps almost everything else .

In 2022 these machines are an interesting curiosity and possibly a viable and cheaper alternative to a 486, if one can live with the limitations .

That's my opinion, at least .

Has the mobo manufactures documentation stated that chip is supported by it's chip set??

From memory their pin output was different than other Socket/Super Socket 7 systems. Even though they fit in those cpu socket.

Pentium fpu performance was way better.

Just pulled one from an old ACER Thin Client. There was a sticker over the plastic "Socket 7" cast marking stating "Cyrix GXMedia "

MarkP wrote on 2022-08-11, 06:53:

Has the mobo manufactures documentation stated that chip is supported by it's chip set?? […]
Show full quote

Has the mobo manufactures documentation stated that chip is supported by it's chip set??

From memory their pin output was different than other Socket/Super Socket 7 systems. Even though they fit in those cpu socket.

Pentium fpu performance was way better.

Just pulled one from an old ACER Thin Client. There was a sticker over the plastic "Socket 7" cast marking stating "Cyrix GXMedia "

Most all MediaGX were 486 chips that physically fit into the cheap mass produced socket 7 socket which was wired with 32bit data and video pins instead of the “pentium” pinout.
My thought was something as simple as using a socket 5 would have blocked out a few pins reducing the likelihood of error but I suppose you could still shove their chip into the wrong board.

However…

The socketed MediaGX 120mhz chip I encountered looked like a 486 pin layout (obviously not compatible)
Back then (2001) I didn’t think much of it and offloaded the chip, I only later found out that the very early (circa 1996) MediaGX were not a socket 7 like pin arrangement using pga Instead of staggered

darry wrote on 2022-08-11, 05:30:

IMHO, running the stock Windows 95 install that it came with was borderline masochism, even by 1997/1998 standards

That's my opinion, at least .

Nah, gotta remember Walmart was still selling AST DX2-66 w/ 8mb all the way into 1998

Most folks we’re running old equipment in 1997
My schools Compaq GX180s w/ 24mb of ram on a rare high speed internet connection via Ethernet was extremely fast compared to the 4mb sx25 I was used to and even faster than my pr200 w/ 8mb of ram because of the t1 and more memory

Things were different back then with all manner of old and new equipment floating around.

My school still had Mac pluses, an Apple 2 lab and 286/386sx writing labs
Some of the pluses could go online using an outdated for the time web browser

The fact that Walmart was still selling 66MHz 486s into 1998 does not, IMHO, rehabilitate the Presario 2200 in any way. Running existing old equipment is fine if it still works and is up to the task. Buying obsolete and/or underpowered hardware new is another thing altogether.

The Presario 2200 may be an interesting artefact nowadays, but back in the day in was seen as an unupgradable piece of extra slow crap by pretty much everyone I knew, including those who were stuck with one .

It

a) was slow in Windows 95
b) had no USB ports (TBH, can't fault it that much for that given the timeframe)
c) had a single 8-bit ISA slot with a dial-up modem inside

Consequently, if one wanted to

1) add a scanner? It better be a parallel port one
2) get broadband Internet ? Chuck the modem, find a 16-bit ISA NIC that supports 8-bit mode and file away the 16-bit part so you can fit in the 8-bit ISA slot (AFAICR, it would not fit otherwise)
3) Want to add a webcam ? Get a parallel one and hope it plays nice with the scanner (if you have one)
4) Want to add anything else that isn't parallel or serial ? Tough luck

It would not have cost Compaq that much more to at least allow some degree of expandability on the 2200 as it was obviously long in the tooth even at launch in 1997.

I got lucky and scooped up a new old stock ECS P5GX-M motherboard off ebay a while ago. It cost more than what I'd be willing to spend for retro hardware but I have a bit of a 486 obsession and could not resist promises of "world's fastest 486". The board has 2 PCI and 2 ISA slots and I paired it with a MediaGX 266 I've had years. Some notes that might help:

- The integrated video card is... a bit of a dumpster fire. A dumpster fire someone tried to put out with dumpster juice mixed with old diesel fuel. It runs poorly in dos (performance-wise) and can be very buggy in windows
- The on board sound card is OK in dos - not the greatest OPL3 emulation but it does work. But again, it is very slow in windows 9x games, causing stuttering and even issues during FMV playback in games like Red Alert 1
- The motherboard has no L2 cache witch is a crying shame. Paired with a Voodoo 2, the mediaGX gets some respectable numbers in GLQuake - perfectly playable at 640x480, and in quake 2 it's... cinematic but sort of playable. Judging by how other machine's performance scales with presence / absence / size of L2 cache, I think adding a mere 256kb could have made a huge difference. Still, impressive performance for what is essentially a cyrix 586 CPU running at 33mhzx8.
- Using a dedicated 2D card (S3 virge) and sound card (SB16) even red alert 95, starcraft and age of empires are quite playable on my GX rig - close to a pentium 120, maybe even 133 at times (for games that are not FPU intensive that is) Performance is good but it has moments when the PC slows down or even freezes for half a second in these games - like it's trying to load something.

Overall, an interesting platform, but very poorly put together. I know they were going for dirt cheap, but in 98 sram chips were not that expensive - they could have added 256k of L2 cache on the mainboard without increasing cost by much. Also, I think the CPUs could handle higher FSB speeds - especially after reading trough feipioa's threads. I mean if a 100Mhz socket 3 586 can handle 66x2, I don't see why the 266MHz mediaGX can't do 66x4. That would have increased memory performance and overall smoothness greatly, making it an actual competitor to entry level pentiums and the K6, even without L2 cache.

Socket3 wrote on 2022-11-04, 20:44:

I got lucky and scooped up a new old stock ECS P5GX-M motherboard off ebay a while ago. It cost more than what I'd be willing to […]
Show full quote

I got lucky and scooped up a new old stock ECS P5GX-M motherboard off ebay a while ago. It cost more than what I'd be willing to spend for retro hardware but I have a bit of a 486 obsession and could not resist promises of "world's fastest 486". The board has 2 PCI and 2 ISA slots and I paired it with a MediaGX 266 I've had years. Some notes that might help:

- The integrated video card is... a bit of a dumpster fire. A dumpster fire someone tried to put out with dumpster juice mixed with old diesel fuel. It runs poorly in dos (performance-wise) and can be very buggy in windows
- The on board sound card is OK in dos - not the greatest OPL3 emulation but it does work. But again, it is very slow in windows 9x games, causing stuttering and even issues during FMV playback in games like Red Alert 1
- The motherboard has no L2 cache witch is a crying shame. Paired with a Voodoo 2, the mediaGX gets some respectable numbers in GLQuake - perfectly playable at 640x480, and in quake 2 it's... cinematic but sort of playable. Judging by how other machine's performance scales with presence / absence / size of L2 cache, I think adding a mere 256kb could have made a huge difference. Still, impressive performance for what is essentially a cyrix 586 CPU running at 33mhzx8.
- Using a dedicated 2D card (S3 virge) and sound card (SB16) even red alert 95, starcraft and age of empires are quite playable on my GX rig - close to a pentium 120, maybe even 133 at times (for games that are not FPU intensive that is) Performance is good but it has moments when the PC slows down or even freezes for half a second in these games - like it's trying to load something.

Overall, an interesting platform, but very poorly put together. I know they were going for dirt cheap, but in 98 sram chips were not that expensive - they could have added 256k of L2 cache on the mainboard without increasing cost by much. Also, I think the CPUs could handle higher FSB speeds - especially after reading trough feipioa's threads. I mean if a 100Mhz socket 3 586 can handle 66x2, I don't see why the 266MHz mediaGX can't do 66x4. That would have increased memory performance and overall smoothness greatly, making it an actual competitor to entry level pentiums and the K6, even without L2 cache.

"Enjoy" the MediaGX experience for what it is . 😉 266MHz is probably significantly faster than the 180MHz CPU in the Presario 2200 .

A friend of mine had a Cyrix 6x86 P150+ (the board did have L2 cache) with a first gen Voodoo and it was far from unplayable in GLQuake . I wonder what a 266MHz clocked MediaGX would be comparable to on the socket 7 front (as far as integer heavy stuff goes).