If like all the other Asus MEW boards (MEW-AM, MEW-L, MEW-RM, etc) you need a board rev that is above 1.00 and a BIOS update to support anything but Celeron to 500Mhz.

SamsungASUS wrote on 2022-03-13, 18:31:

Hi, I had recently tried to upgrade the CPU that came with my HP Pavilion 6545c that has a Asus MEW-VM motherboard. The original CPU is a Socket 370 Intel Celeron 500MHz with 128k L2 Cache and 66MHz FSB. I tried some Socket 370 Intel Pentium 3 CPUs with 256k L2 Cache and 100MHz FSB. The Asus MEW-VM motherboard wouldn't start with any Intel Pentium 3 CPU. I'm not sure if there's a problem in that the motherboard can't recognize a higher L2 Cache, or if it fails to run at 100 or 133MHz FSB.

Neither. It's the pinout "So370" had multiple implementations. Asus' ME-series boards had So370 PPGA pinout, only used by Mendocino core Celerons. Coppermine core Celerons and P3 CPUs used FC-PGA pinout, which was subtly different. You could run a PPGA Celeron on an FC-PGA socket, but not the other way round. Lots of info (including mods you can do) here: Socket PPGA and FC-PGA Slot-1 Slotkets.

Voltage requirement was also lower which may additionally cause the board not to boot if the CPU requests a voltage that the VRM can't supply. This can also be modded out, hard-coding the board to supply 1.8V which is within both abilities of older So370/Sl1 VRMs and max voltage spec of CuMince CPUs.

Asus does list the P3 650 to 850 for MEW-AM and RM. Using cpu-upgrade.com it shows as coppermines as supported but only on board revs above 1.00 and certain
Asus probably reworked the later rev boards, and most need a BIOS update .....just an observation.

Horun wrote on 2022-03-13, 23:51:

Asus does list the P3 650 to 850 for MEW-AM and RM. Using cpu-upgrade.com it shows as coppermines as supported but only on board revs above 1.00 and certain
Asus probably reworked the later rev boards, and most need a BIOS update .....just an observation.

This is kinda an oddity in a way. I've always seen ASUS use nomenclatures which approximate their compatibility.
P2L slot 1 Pentium 2 440LX, P2B slot 1 Pentium 2 440BX, P3B slot 1 Pentium 3 440BX, ASUS ME?-?? s370 Mendocino, ASUS CU?? s370 Coppermine (with CU being the chemical element Copper which in latin is cuprum), ASUS TU??? s370 Tualatin.
The third letter for s370 boards was often the designation for the chipset used.
MES = Mendocino s370 board with SiS chipset, MEL = Mendocino board s370 440LX, MEZ = Mendocino s370 440ZX, MEB = s370 Mendocino 440BX
This is not 100% foolproof btw, but it does make it easier to see what board you have on hand without having to look up the model number first (or from knowing from top of your head).
MEW = Different, i810 chipset and does support Coppermine CPUs (in some cases!). Usually highly integrated boards, usually not very recommended because i815 and 440BX are usually just plain better. i810 doesn't even have AGP and has some other limitations so it's the odd one out for multiple reasons.

I agree ! the name of this board does not fit with Asus typical naming schemes.