I've been also messing with a GXm lately. The idea of a mATX 486-class build seems weirdly appealing to me, and it's hard to explain why.
In practice a 486 is just slower than a Pentium, and the same applies to MediaGX. Can't remember major games or programs that flat out refuse to run on a 486, but run on a classic Pentium or vice versa, so the difference in mostly in architecture of the chip, if that appeals to you.
A MediaGX will have things like branch prediction disabled by default, but that is also mostly a matter of performance.
So in short — IMO a fast MediaGX system will perform about as much as a Socket 5 system, you won't really feel the difference. With MMX this becomes similar to a Winchip. The unique part is video (kinda broken in DOS) and sound (decent SB16 emulation, but I still don't know why you would use that over a proper ISA sound card).
Currently I'm trying to assemble a full collection of reference drivers for the platform for all operating systems (Win95, Win 3.1, DOS, NT, etc). That has proven weirdly difficult because neither Cyrix nor National Semiconductors have hosted them — only provided them by request.
What i like from MediaGX CPU is for what i read in some datasheet, is *simplifying* just a cyrix 5x86, in different socket
But MediaGX and GXi are just up to 180mhz, and without l2 cache, i really dont think will be much if any faster than my current 5x86
I was reading this datasheet for the GXm, and *I* think, maybe mistake, the new GXm have a lot of full pentium instruction set, is not a "486" anymore, CPUID, CMPXCHG8B, RDTSC, RDMSR, WRMSR, RSM etc
For me buying this GXm motherboard is more than one week payment (6 days exactly), thats why i want to be sure, and ask oppinions here. If is a cheap motherboard, i will buy and test myself! but for me is a big investment
Hi! finally i decide to buy the MediaGXm motherboard, was super expensive, but i take the risk
And my DREAMS BECAME TRUE!!! is...
AMAZING
Is just what i was looking, a faster 486 (5x86 in this case)
The motherboard i buy was a IT-586GXM+, it came with a GXm 266mhz. My actual 486 motherboard is a AB-PB4 1.2 with a 100mhz cx5x86. After many test, i realize the GXm is just a faster 5x86, nothing more
It supose have MMX instructions... but NOTHING I TESTED that use mmx get any speed improvement at ALL, like ZSNES or Callus. I think maybe MMX must be disabled with this board ?
It supose have RDTSC instruction, but again, is not working at ALL. Emulator like Genecyst that have a great improvement using RDTSC instruction in pentium, crash in GMx exactly like in the 5x86... in GXm papers i read say this CPU support RDTSC instruction... is clear or not exist or is not enabled
The onboard audio and video are trash anyway
Finally after some days of testing i decide to start upgrading my 486 computer with the GXm, i feel comfortable, i feel im using my old 486 just faster!
- No PS/2 for mouse - Max 8GB HDD
- More ISA and PCI, have EISA (but never used it)
- Have L2 cache
GXm
- No L2 Cache - Only 2 PCI and 2 ISA
- Have PS/2 mouse
- Have USB !! nice!
- 32GB HDD support
- ATX support (great, more easy to replace psu)
- Onboard joystick port that work even disabling audio
I did some test, comparing Fastdoom, and compare too with my IBM 486DX4-75mhz 8KB L1, 256KB L2 overclocked to 100mhz, with CL5424 integrated video just for test
15x86 - 50.33fps 2GXm - 116.89fps 3DX4 - 41.56fps
The 5x86 is 20% faster the DX4 but in this case, the CL card is slower the ARK LOGIC ark2000 i used in both the 5x86 and GXm, difficult to say how much faster is the 5x86 16KB L1 CPU with same graphic card
The GXm is like having a 233 5x86 in Doom, is clear the CPU speed is more or less... or exactly the same, exept L2 cache difference, ram timmings etc
I testest 486 Quake https://github.com/goshhhy/486quake i used 486 quake in the 3 computers, 586 and 686 versions are slower even in GXm, is pretty clear the gxm is a 486, no pentium+ optimizations works
15x86 - 15.26fps 2GXm - 36.8fps 3DX4 - 9.6fps
I think results are very similar to doom, and DX4 suffer the worst FPU
I tested my other thing but are more difficult to benchmark, for example, callus emulator running SF2 CE, in the 5x86, 320x240, 11khz audio, is frameskipping 2-3, i guess work at 20-30fps, and in GXm is full speed, but just on edge, if I use 22khz audio for example, i have frameskipping or slowdown. Comparing, i have a Pentium 166mmx PC, and callus with fpucopy and mmx, is working fullspeed with 44khz audio
Just for finish, im very happy with the GXm, finally i have the Super 486 i dream when was a kid, i love this CPU
