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My Gateway 2000 P5-120 is stuck at 90MHz. What setting fixes it?

computerdude92

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Hi guys,

I found a Gateway 2000 P5-120 fulltower that looks just like the one pictured below. It was manufactured in Feb 1996. The system works great and all, but the CPU speed is reported at only 90MHz, not the 120MHz we want. I checked under the hood and the CPU is indeed a real Pentium 120.

The motherboard has several dip switches to control settings instead of jumpers. I saw a row for CPU speed and the only options are 75, 90, and 100. This is the original motherboard for the system because it has a sticker with the same exact date as on the back of the PC tower, being Feb 29, 1996. Does anyone have a manual handy, or has a Gateway like this that has the switches set correctly so I can find out what the right settings are please?

Thank you very much for any answers.

Click image for larger version  Name:	p5-120.jpg Views:	0 Size:	33.3 KB ID:	1233103
 
Which motherboard is in it? Gateway used a couple of different boards at that time.

You may want to get a speed testing tool. 90MHz might be the correct setting. The 90 MHz Pentium has a 1.5 multiplier so the bus speed is 60 MHz. The 120 MHz Pentium has multiplier of 2 which means the correct bus speed is 60 MHz. Yeah, it means the motherboard design did not get new labels when the new processors were made.
 
According to this Vogons thread:
https://www.vogons.org/viewtopic.php?t=51703

This is the motherboard it uses:
https://stason.org/TULARC/pc/motherboards/I/INTEL-CORPORATION-Pentium-ADVANCED-ATX.html

It should support non-MMX Pentiums up to 166 MHz.

If you can find one of the now rare Evergreen Spectra upgrades, you can get the machine up to 333/400 MHz AMD K6/2. I had one back in the day, and it was nice. The 66 MHz FSB is limiting though, it won't perform the same as a motherboard with a native 100 MHz bus.
 
I hang out with my bff on Wednesdays, so I'll try to remember to check what motherboard it has when I'm at his place.
 
Depending upon how old the BIOS is, it might not be able to report speeds faster than 90MHz. I've seen this with some laptops I worked on way back then. A BIOS update sometimes solved the issue, but a few motherboards just couldn't handle the faster CPU's even with an updated BIOS. Rare, but it did happen. AMD K6 processors used tricks with the multiplier table Intel used for the Pentiums in the socket 7 motherboards and used the 3x or 4x (haven't checked - too many years ago) as a 6x multiplier for their CPU's. So even if the mobo didn't support 6x you could kick it up a notch. Assuming the K6 played nice with the BIOS and mobo.
 
Depending upon how old the BIOS is, it might not be able to report speeds faster than 90MHz
Unlikely, since that is not a custom-built PC but one actually sold as a P5-120 by Gateway 2000.

Of course, the mainboard may no longer be the original one. Post a picture of it, please.
 
Of course, the mainboard may no longer be the original one. Post a picture of it, please.

That's kind of what I was suspicious about. Could be that the original MoBo failed and someone dropped in something close that only supported up to 90MHz.
 
I finally remembered to post these. I hope this is enough info to change the CPU speed from 90 to 120MHz.
Many moons ago i had one of those systems though i scrapped the case and kept the innards, My board has a different layout to yours and is dated 17/06/95 but runs at 120Mhz, I have attached pics of the switch and 2 relevant pages of the manual that may help, The switch settings on mine are:
1 = OFF
2 = ON
3 - 4 - 5 = OFF
6 = ON
7 - 8 = OFF

switch.jpg
1.jpg
2.jpg
 
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I recently tested the exact settings you gave me, as my PC looks to have very silmilar looking switches. It made the CPU go from 90 to 75MHz... So it looks like there's nothing I can do. The board indeed looks like an older model that Gateway 2000 put in by mistake. The 2/29/96 date code is the same on all other parts of the system. No setting is available for the Pentium 120 that originally shipped with the system. Only 75, 90, and 100MHz Pentiums are supported.

The other switch setting I changed as per your instruction fixed the green boot-up graphical glitches. Must have been a wrong voltage setting. I'm glad the system runs healthier now. No need to replace the video card. Thank you for the help, Malc.
 
Just because a board doesn’t have a multiplier jumper doesn’t mean it can’t be hardwired for a different multipler

You would need to check the BF pins (see socket 5/7 pinout) for multiplier pin locations

If the multiplier pins are floating you can simply wire wrap the cpu side pins to manually set ground or whatever to drive the multiplier

If you want to be real fancy and can find the traces to the pins you can determine if they are wired to a jumper, if not you could cut the trace and make your own jumper.

Lastly there are overdrive interposer sockets that can fit into your board providing any voltage and multiplier, could even drop in faster cpus if you wanted with such a device
 
Too much work, just grab a k6-2 233 66mhz bus cpu, set the multi to 1.5x and call it done. You can find em on cpuworld sales section on the forum for under 20 dollars shipped usually. Make sure to set the voltage to 3.1-3.3v setting and throw a small fan on the heatsink.
 
There is no way to set the multiplier to 1.5x on this board. Only 2x/3x and 1x/2x settings are available as pictured. I believe my mobo has the same switch block as Malc does, just no Pentium 120 support.

I see on cpu-world.com that a K6-2 233 with 66 FSB has a multiplier of 3.5x. How does it work at 1.5x?
 
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So I just checked on the Pentium 100MHz on cpu-world.com and it supports 1.5x (66 MHz FSB) or 2x (50 MHz FSB)

Seeing the dip switch settings on my mobo, it looks like the only option for a Pentium 100 would be 2x (50 MHz FSB) That makes my board look older than I thought, despite the 2/29/96 date sticker. (It can't do 66 FSB on a P100)

Looking at those pictures of my mobo again, I see it has a 430FX chipset.

Sounds like a dated choice for an early 1996 board...

Pentium 100 is the fastest CPU supported on my board, it says so on the PCB. I wonder how you would trick the multiplier to have the mobo correctly work with a K6-2 233 with 1.5x, as twolazy suggested...

------------------------------------------------------------------------------------------------

Would an AMD K5 work?
 
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Checking my Upgrading and Repairing PCs 12th edition book by Scott Mueller, I see that the 430FX chipset came out in Jan 1995. The 430VX and 430HX came out in Feb 1996.

So that means my mobo, being dated 2/26/96 was one of the last FX boards manufactured as the VX chipset was taking over.

On cpu-world it says the Pentium 120 was first manufactured on 27-Mar-95. I wonder why it won't work with my board correctly...
 
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Pentium 100 is the fastest CPU supported on my board, it says so on the PCB. I wonder how you would trick the multiplier to have the mobo correctly work with a K6-2 233 with 1.5x, as twolazy suggested...

There is no trick, it's never going to work. You have a Socket 5 motherboard and are trying to install a Socket 7 CPU. There's a non-trivial difference between the two where the I/O and core voltages are split on Socket 7 to allow for lower core voltages while maintaining the 3.3v I/O. Installing the latter in the former at best will not work and at worst, fry the CPU because of the excessive core voltage being smashed into it.

The only way that you'll be able to upgrade is by using an interposer, like was used with the Evergreen Spectra 333/400 or other similar interposer designs. You may also have to modify the BIOS to add microcode for the CPU that you want to use, which may or may not be possible.

Would an AMD K5 work?

I don't know why you'd want to go with an AMD k5, that's a significant downgrade from a Pentium in both integer and especially floating point performance. It probably wouldn't work regardless, Intel was extremely hostile to 3rd party x86 at this point in time and most of their OEMs didn't have BIOS support for non-intel parts, even though the chipset theoretically did support them.
 
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