retro games 100 wrote:

Regarding the Gigabyte GA-5AX mobo, it's slowest supported CPU is the Pentium "classic" 133 MHz CPU. That will be using a 66 MHz bus speed, with the CPU's 2x multiplier. Therefore, 66*2 = 133 MHz CPU clock speed. I think this mobo allows you to select a 1.5x multi, but I don't know for sure if it will work with a P-133 MHz CPU. If it does, then you'll get a CPU clock speed of 90 MHz. That's 1.5 * 66 = 90 MHz.

For RAM, you can start off with as little as 8MB.

1.5x is supported by the Pentium non-MMX. Maybe there are other non Intel CPU's that can go even slower, need to do a little searching

Edit: According to this site:
Link: http://mysite.verizon.net/pchardwarelinks/cpuspeed.htm
there may actually be MMX chips with only 1.5x - 3x multi. I never tried myself though, but I guess it makes sense since 233Mhz came a little later?
Apparently there are some older Cyrix and AMD chips which support 1.5x multi, but especially for the Cyrix, I don't know about compatibility for them.

Also these chips are a bit harder to find anyway.

If it does, then you'll get a CPU clock speed of 90 MHz. That's 1.5 * 66 = 90 MHz.

Er, math fail... 1.5 X 66 = 100mhz.

According to the manual, though, it does support the 1.5x multi, with the three switches on (or off? It lists the settings with X's and O's, 1.5x is all X's, but it never specifies what the X's and O's mean.). You might also have an undocumented slower bus speed, try the four bus speed jumpers all set to the 2-3 position... I'd suspect that might give you 60mhz.

Old Thrashbarg wrote:

If it does, then you'll get a CPU clock speed of 90 MHz. That's 1.5 * 66 = 90 MHz.

Er, math fail... 1.5 X 66 = 100mhz.

According to the manual, though, it does support the 1.5x multi, with the three switches on (or off? It lists the settings with X's and O's, 1.5x is all X's, but it never specifies what the X's and O's mean.). You might also have an undocumented slower bus speed, try the four bus speed jumpers all set to the 2-3 position... I'd suspect that might give you 60mhz.

Oh cmon...it's sunday. Cut us some slack ;D

And the 3rd multi jumper is ignored by all CPU's that don't support them 😉

Oops! Sorry about the math(s) fail! 😊

Old Thrashbarg wrote:

If it does, then you'll get a CPU clock speed of 90 MHz. That's 1.5 * 66 = 90 MHz.

Er, math fail... 1.5 X 66 = 100mhz.

According to the manual, though, it does support the 1.5x multi, with the three switches on (or off? It lists the settings with X's and O's, 1.5x is all X's, but it never specifies what the X's and O's mean.). You might also have an undocumented slower bus speed, try the four bus speed jumpers all set to the 2-3 position... I'd suspect that might give you 60mhz.

I've just fired up this Rev 5.2 GA-5AX mobo (fired not fried 😉 ), and I am happy to report that your suggestion of setting all 4 of the mobo's bus speed jumpers to the 2-3 position yields an undocumented bus speed setting of 60 MHz. I put in a regular/classic Pentium 90, and ChkCPU.exe reports it running at 90 MHz, with the mobo's multiplier set to 1.5x.

I wonder why Gigabyte decided to omit this information from both their manual, and also from the bus speed settings info printed on the mobo's PCB? BTW, the X's and O's in the manual represent Off and On, respectively.

I wonder why Gigabyte decided to omit this information from both their manual, and also from the bus speed settings info printed on the mobo's PCB?

Probably at the time the motherboard was released, they didn't expect anyone to be running a 60mhz bus anymore. I mean, the board came out in '98 or '99, well into the K6-2 generation, and those CPUs didn't use the 60mhz bus. Also, even people using PMMX chips would have been using the 66mhz bus... I think the only 60mhz PMMX chips were mobile versions. So the only people who would have needed the 60mhz setting were the ones who were still using the old P54 chips, and not too many of those sorts would've bought a SS7 board without also upgrading their CPUs.

OK, thanks for the explanation. Just a thought however: what speed would the PCI bus be running at, if the mobo's FSB was running at 60 and not 66 MHz? Would it be slightly less than 33 MHz? Is the PCI bus OK to be run at slightly less than 33 MHz?

retro games 100 wrote:

Oops! Sorry about the math(s) fail! 😊

That's what you get for using a first generation Pentium 60/66 with the math bug.

The PCI is probably running at 30mhz, and the AGP at 60. It'll work fine, you'll just lose a bit of performance that way. That was pretty much standard for the lower-speed Pentiums, the 60mhz bus ones ran 30mhz PCI on all boards AFAIK, and the 50mhz bus ones (which only included the 75mhz chips I believe) had a 25mhz PCI speed. That's likely one of the reasons the lower bus speeds fell out of favor.

Old Thrashbarg wrote:

I wonder why Gigabyte decided to omit this information from both their manual, and also from the bus speed settings info printed on the mobo's PCB?

Probably at the time the motherboard was released, they didn't expect anyone to be running a 60mhz bus anymore. I mean, the board came out in '98 or '99, well into the K6-2 generation, and those CPUs didn't use the 60mhz bus. Also, even people using PMMX chips would have been using the 66mhz bus... I think the only 60mhz PMMX chips were mobile versions. So the only people who would have needed the 60mhz setting were the ones who were still using the old P54 chips, and not too many of those sorts would've bought a SS7 board without also upgrading their CPUs.

The P55C (Pentium MMX) was available in 120 and 150mhz variants so the 60mhz bus would have still been in use for those chips, though most likely in laptops. I can't recall off the top of my head if there was ever a desktop variant. There was also a Pentium Overdrive with MMX technology that could run on 50,60, or 66 mhz bus boards.

I'm pretty sure all the 60mhz MMX chips were intended to be mobile-only. Some of them could've made it into desktop systems, I suppose, but at the very least it wasn't common.

And as far as the MMX Overdrive chips, again, how many people would've been using one on a SS7 board? Those things were designed for upgrading older Socket 5 boards, and they were getting pretty long in the tooth by the time that GA-5AX was released, so it's not likely that many people would've carried them over.

Indeed, there were mobile MMX chips made with the standard PGA, but at the time there was no real reason to ever try one in a desktop motherboard. These were always intended to be used in mobile computing solutions and I guess it made it into Socket 7 format because many laptops at the time also used a Socket 7 ZIF socket (maybe it was cheaper that way).

Link:
http://www.cpu-world.com/CPUs/Pentium/TYPE-Mo … tium%20MMX.html

Tetrium wrote:

Indeed, there were mobile MMX chips made with the standard PGA, but at the time there was no real reason to ever try one in a desktop motherboard. These were always intended to be used in mobile computing solutions and I guess it made it into Socket 7 format because many laptops at the time also used a Socket 7 ZIF socket (maybe it was cheaper that way).

Link:
http://www.cpu-world.com/CPUs/Pentium/TYPE-Mo … tium%20MMX.html

Was that a low voltage chip or did it use the same voltages that desktop motherboards used? If it used voltages not found on a desktop motherboard then you'd probably need some sort of voltage regulator to use it in a desktop.

sliderider wrote:

Tetrium wrote:

Indeed, there were mobile MMX chips made with the standard PGA, but at the time there was no real reason to ever try one in a desktop motherboard. These were always intended to be used in mobile computing solutions and I guess it made it into Socket 7 format because many laptops at the time also used a Socket 7 ZIF socket (maybe it was cheaper that way).

Link:
http://www.cpu-world.com/CPUs/Pentium/TYPE-Mo … tium%20MMX.html

Was that a low voltage chip or did it use the same voltages that desktop motherboards used? If it used voltages not found on a desktop motherboard then you'd probably need some sort of voltage regulator to use it in a desktop.

My thought also. But generally one could say that these mobiles were nothing but underclocked and undervolted desktop parts anyway. From a retro perspective these weren't very interesting (unless you collect CPU's).
The only mobile Pentium 1's I like are the PGA Tillamooks 😉