I have a IBM Aptiva E6U running at 400 mhz, It is a slot 1-Pll with 100 mhz fsb, now can I install/upgrade to a 700 mhz Plll slot 1 ??

Only if the BIOS supports, alternatively ? http://www.powerleap.com/PL-iP3T.jsp

if it came new with pentium 2 400mhz then it is likely it can only take slot 1 cpus that take 2.05volts and not the later ones that are something like 1.65-1.75 volts. The fastest I have seen of these is the pentium 3 600mhz - but you have to be careful as there are other versions out there that are not 2.05v and might not be 100mhz fsb.. It will show the voltage on the details printed along the top black plastic edge along with speed , cache and fsb. Much more easily obtained is the p3 550mhz or the p3 500mhz (but you sshould still check the fsb and voltage). I have also used those slot 1 to socket 370 convertors - there are good ones (like ones from MSI with plenty of jumpers on) and cheaper generic ones that seem to work on some motherboards and not others. The chances are your mobo has max 100mhz fsb so you need to use 66mhz (celeron) or 100mhz FSB socket 370 cpus

The Motherboard is a Intel 440 BX....

"if it came new with pentium 2 400mhz then it is likely it can only take slot 1 cpus that take 2.05volts and not the later ones that are something like 1.65-1.75 volts." All of the BX boards I've worked with took 1.7v Coppermines--and even 1.475v Tualatins on cheap Slockets without any voltage regulation of their own! As samsung wrote, the BIOS is what you should be paying attention to. Because most board manufacturers offered P3-aware firmware for their boards, it shouldn't be a problem. On the few BX boards that didn't receive a P3-aware BIOS update, the P3 would most likely be seen as a high-clocked P2 (no SSE). The worst case scenarios: a Coppermine's on-chip L2 cache won't be detected, or the board won't POST. You WON'T fry the chip, however. You should have no problem with BIOS support, since the PC is made by IBM. Super P3-Now with Blu-Ray playback! PIII-S @ 1.66GHz 2GB PC2700 AGP HD3650 LiteOn BD-ROM Homebuilt 1080p projector w/ Pixelworks HDMI controller JBL 5.1 audio

You might check this previous post with essentially the same motherboard: http://www.computing.net/answers/ha... If your motherboard was made by Intel it should have a part number starting with AA on a sticker on the board. There used to be (and may still be) an Intel page with the highest processor supported by the motherboard, based on the AA number, and the bios version necessary to support that cpu. Lenovo, where IBM dumped support for its old stuff, doesn't show support for that model. I came across this bios upgrade: http://members.driverguide.com/driv... I don't know what version that is but you may find others with a more specific search. If you download from driverguide use the 'view a series of ads' option and then keep clicking 'no thanks' or 'continue' or whatever it takes to get to the next one. (There's only 5 or 6 ads. If you register they will limit your downloads--a**holes!)