Sorry, i am new to some of this. Everyone i have talked to so far shuts me down because i dont know everything about it. That is why i am asking questions, so please bear with me.
I have a celeron d 352, 3.2ghz, 533mhz processor. I was looking into getting an upgrade pentium 4. I have found one that is a 3.6ghz, but has a bus speed of 800 and hyper threading. My mother board says it supports 400/533/800. Does this mean it will support this cpu, or do i have to match it with the old cpu 533?? Do i have to just interchange my memory to match the 800? Please help, i have researched and read, but everybody that asks questions seems to be ahead of this point, or already knows about it. Thanks,

It must be equal to or faster... but will run at the maximum speed of the front side bus, regardless of what speed it is otherwise capable. There are all sorts of problems that come up when you change the cpu only on a standard computer brand and model... and changing from a Celeron to a Pentium is a key one in certain brands and models. HP's, for instance, are particularly difficult. You might need to do a series of Gurgle searches to track it down.

i have a lower end emachines t3524 with an msi rc410?? i believe motherboard. I wanted to upgrade to a pentium 4 661 cpu with 3.6 ghz, 800 bus speed. everything else says it should work fine, but i wasnt sure about the bus speed. Would it be better to just get a motherboard/dual processor combo? are the motherboard fairly universal? Thanks

You are getting off into a new world of what things cost, what parts work, and what components are compatible.
If you are replacing the motherboard, you usually are also replacing the memory, and the power supply, and the operating system. It gets complicated. It certainly gets expensive.

so, it would be better to upgrade just the cpu until i have enough money to put into a better computer. From what you said, i would be able to put the p4 3.6ghz 800 fsb into my computer, but it will only run at 533? it will work though?? It will still retain the higher cache memory and 3.6ghz processor speed?? That is my understanding at least, please let me know otherwise. Thanks
Doug

Your computer's speed is not all about the processor. How much RAM do you have? Also, if you are using the same motherboard make sure the socket is compatible with your P4 processor. It usually is either LGA775 or Socket 478.

yes, it is a 775. I have 1.5 gig ram. lots of hard drive. I have limited it down to the cpu. all i want to know is if an 800mhz will work in my motherboard. will it just run at 533, or will the memory not match up. I have speedfan, and see that you can adjust the fsb, but i havent messed with it yet. somebody please answer these few questions. Thanks
Doug

Who makes the MOBO and you should email them and ask if your MOBO (motherboard) can it support 800MHz bus with HT. That's the only way you're going to know for sure. Or just replace the MOBO with some more current and you don't have to worry about that bus speed.

ok, according to cpuz, it is an intel D102GGC2. Here is what intel says it will support. http://support.intel.com/support/motherboards/desktop/d102ggc2/sb/CS-026580.htm

im looking to put the p4 661 in. all i want to know is if it is 800mhz, and mine was 533 that im taking out (celeron d 352), will the new one work properly?? do i have to match my memory to the new processor, or what would need to be done?

The answer is in that post. It gives you the speed, the BIOS, and the chip numbers that will work. My guess is that no others will work, but those listed.

does the memory speed have to match the cpu speed. will my 533 memory work with a new 800 mhz cpu, or will it slow the cpu down? or vise versa?

they don't have to be the same speed, but strap is important. You have to see what speed ram the motherboard will take.

No, it does not need to match the cpu speed, and will not slow down the CPU. Just meet the specifications of the system board, or the manufacturer brand an model.
It usually has to meet a few motherboard requirements, which you may have to look up at the motherboard or manufacturer web site. This is way a site such as www.Crucial.com is helpful, though they have a disclaimer saying their specs are secondary to the manufacturer specs.
ECC or No ECC. Some will not accepte ECC memory. Others require that all memory be ECC or Non-ECC. Still others will detect if the module is not ECC and will run all other ECC modules as non-ECC.

Cannot exceed the memory module capacity.
Usually cannot exceed the memory speed as designed into the board, so the specifications of the motherboard or the computer brand and model are critical. High speed or high performance memory will not work on some motherboards. Again, the specs will tell you.

Some ASUS motherboards are very picky, and will not accept certain brands of memory that do not meet timings and latency specifications.
There is a long list, but you don't have to worry about the questions you asked.
Memory does work better if all modules are the same speed. Otherwise, they will work at the speed of the slowest module.

Looks like you can do what you wanted to do with those specs on intel set. If you're in doubt send email to intel and they'll give you the answer. Otherwise you should be okay. Now Memory a lot of RAM eventhough clocked higher can be adjust to lower speeds. In the past 100 to 133Mhz didn't work well today DDR and DDR2 over comes that issue..