Hi, I'm new to the forums and I've been using Linux for a few months now. I'm all settled in and I know my way around it.
I bought a new Pentium 3 from eBay and I installed it fine but it only gave me 50 more Mhz. From 600 to 651 as oppose to 866. I've searched for nights on end for some way of fixing this, in an easy manner but I haven't found anything.
My model of motherboard is GA-6WMM7 and I just thought you guys might be able to help me.

Thanks in advance

What type of LINUX you've got into?

I'm not sure exactly what you mean.

So lets get this straight,
You bought a new chip but not mobo. Previously you had 600MHz and upon installing the new chip you now have 651MHz despite buying an 866Mhz chip?

If that is what you meant there are three possibilities that I can think of.
1) The chip you bought is a 650Mhz chip and you got ripped off. Check the chip for markings to prove it is what it is supposed to be.
2) You haven't set up the BIOS on the motherboard properly. You will either have dip switches to set or a soft menu in the CMOS setup. i.e. del on boot.
3) Your motherboard is only capable of running a 650MHz chip at the fastest.

Let me know if any of these sound plausible

According to Intel's P3 page there was no P3 650 Mz, so I think it would be very helpful to open a terminal session and enter this command
which will simply display information about your CPU. It looks like your mobo supports over/under clocking via BIOS, and at this point, suggestion #2 from fraz's post seems most likely. Please post back with the results of the "cat" command above

If it's a mobo setup issue, it might be worth flashing your BIOS to the latest version as a lot of motherboards increase the maximum CPU clock through BIOS upgrades (to an extent) between the first version and last. I know a board I had added 100 MHZ or so through BIOS upgrading. So worth checking anyway.

tommy@linux:~> cat /proc/cpuinfo
processor : 0
vendor_id : GenuineIntel
cpu family : 6
model : 8
model name : Pentium III (Coppermine)
stepping : 10
cpu MHz : 651.530
cache size : 256 KB
fdiv_bug : no
hlt_bug : no
f00f_bug : no
coma_bug : no
fpu : yes
fpu_exception : yes
cpuid level : 2
wp : yes
flags : fpu vme de pse tsc msr pae mce cx8 sep mtrr pge mca cmov pat pse36 mmx fxsr sse
bogomips : 1303.82

That's the reply to the command you guys kindly prompted.
I'm not really that familiar with flashing and I couldn't find any BIOS upgrades. I wouldn't know about how to do it anyway lol. Any more help would be greatly appreciated. Thanks for all your help so far!

When you switch on the machine 1st time, what does the initial screen say about your chip and motherboard revision. It is hard to tell you where to look given that I'm not familiar with your motherboard but in the first few lines it will tell you the BIOS version on your motherboard, (unless you know it anyway) then under it will tell you what it thinks the CPU is which will likely be Pentium III 650MHZ. What it thinks may be based on some settings that are set up on your motherboard either by dip switches which will be in a little block of about 10 or 15 switches perhaps or it will be a software setting in the BIOS setup ie when it asks you to press del (or F2) to enter setup, there may be settings there OR it could autodetect the CPU.

The first two mean that you will need to figure out, with the manual how to set up the CPU.
The latter means that the CPU will automatically be configured and if correctly so then your chip isn't an 866MHZ or the fastest chip your mobo can handle with its current BIOS is 650.

Now the way that chip clockspeed is determined is based on the clockspeed of the front side bus (FSB). This has an unchangable value say 133MHz for the era your chip is from. There would then be a setting in the BIOS or via dip switches which set the multiplier for the chip clock speed. This means that the chip clock speed would have to be a multiple of 66 MHz in order to get its intended speed. i.e. for 866MHz this would be 6.5 x 133 MHz. 650 would be around 5 x the FSB speed. So if you understand that, you can figure out what the multiplier should be. If it is at it's maximum in the BIOS settings then you almost definitely need to check if there is a BIOS update (or check the chip is genuine). If not you need to set it correctly.

Incidentally this was how early overclocking was done before BIOS began to support it. All you did was set the multiplier high than it was supposed to be in order to get faster clockspeeds. The only reason I mention this is because your chip is underclocked.

On the bright side it will last longer.

Let me know how you get on finding out BIOS version and reported clockspeed (by the BIOS)