I'm currently looking to upgrade my CPU. My current one is a PII 350, and my MB is an Aopen Ax6bc. According to what I can find, the maximum CPU it can handle is a PIII 850. However, I have seen posts where users, using a slotket, have much more powerful CPUs. Am I able to use say a PIII 933 in the standard slot, since with slotkets, much more powerful CPUs may be used. If not, then why?
Four things determine max CPU:
1) pinout. P3-850 is an FC-PGA CPU, as are all other Coppermine CPUs. Wrong pinout (eg. FC-PGA2) and you need to mod stuff to make it work.
2) voltage. Your board can (if it supports P3-850E) supply the necessary voltages for Coppermine CPUs but not for Tualatin. Note that this typically differs per PCB revision of your motherboard, so be sure to check whether yours supports it. The AX6BC was a classic board that spanned the time of the introduction of Coppermine, so earliest revisions probably don't
3) bus speed support. Your BX board officially supports max 100MHz FSB. You could probably overclock it to 133MHz, but even though the BX is a good overclocker, once you go out of spec, no guarantees, particularly as you're also overclocking things like the AGP port.
4) BIOS support. This goes by CPU stepping (which generally does NOT correspond to speed in MHz). If your BIOS doesn't recognise your stepping it might just work perfectly, it might miss features, or it could entirely fail to boot.
A fifth factor is non-technical: motherboard documentation will generally only include items available at launch of the board, or at the last revision of it. This says exactly nothing about what is possible, but can explain what you are reading.
Now, if you know Coppermine CPUs are supported on the board, 1 and 2 are covered. 3 is clear enough: the Coppermine CPUs with 100MHz FSB ("E" suffix) wil work in-spec, the CPUs with 133MHz FSB ("EB" suffix) will work at 3/4 of rated speed without overclocking, or faster if you do overclock, and multipliers are locked. So that P3-933EB is rated to run at 7x133MHz. Run it on 100MHz FSB and it will run at 7x100=700MHz.
That leaves 4. This is a tricky one as you need to figure out what the board actually supports (sometimes you can find it in BIOS release notes, things like "supports cC0 stepping Pentium III CPU"), and then you need to check whether a certain CPU has a supported stepping (run the S-Spec part number through ark.intel.com or cpu-world.com). The last Coppermine stepping was cD0, so if that is explicitly mentioned in release notes, any Coppermine CPU will work. If in doubt, stick to earlier cB0 stepping. The claim that P3-850E is supported is tricky, as you have P3-850E in every stepping from cB0 onwards, so that still doesn't tell you what is supported, let alone what will happen if you try it.
TLDR: go for 100MHz FSB and a high speed, but with an early (cB0) stepping to play it safe.
