celerons have a lower bus speed than pentiums this means that the processor comunicates with the system slower. a celeron is less complex and can perform less operations per clock cycle. also although not so much now the celeron could have less cache memory on it, this is a a small quantity of "ram" like 64-512 KB or in the more modern processorts even 1-2 MB that works at the same speed as the processor and much faster than the system ram memory keeping small amounts of often used info at hand to speed up data transfer. these three things can make two processors of the same clock speed do more or less work "per clock cycle". generally the celeron will not suppot all the multimedia instructions that i am afraid r handy in gaming but if it has the speed it's mathematical section can still do the same job but no so efficiently and it has to do everything as there is no multimedia processor as u may call it althouhg all this is in the same chip. the cheaper AMD cpus (the producers of the athlon and now demised duron) r selling the athlons that have diffective multimedia sections with that section disable so it is like the intel celeron equibvalent these cpus will have only a mathematical section.