Core 2 Duo -vs- Core 2 Quad

First off it depends what you are using the computer for, and what hardware you currently have. Also your budget. Do you already have a motherboard? If not then there is no reason to buy a LGA 775 socket mobo and you should go straight to LGA 1156 or 1366 (i5/i7). If you are on a budget and want to spend under $200 on a CPU, you should take a look into AMD's lineup.

The q9550 basically has 2 e8400 chips on one die. With a little less mhz (obviously).
The architecture of the i7920 and I5 750 are newer, more transistors, faster and efficient.

well if ur thinking of saving money, a q9550 hits the spot, but the 775 socket is pretty much dead as soon as the dual core i5 cpus hit sometime in q1 2010, whereas the 1366 socket will be alive and kicking until intel puts out an octicore, so i would suggest a 920 and an affordable 1366 board, the e8400 is a strong contender if ur budget does not permit you to buy the i7 setup, you can hold onto the 8400 until you get the i7, what do you use ur pc to do? only if i know this can i tell you how much of an improvement you will see

Moderate gaming nothing extreme. Graphics to a certain extent and I do a lot of web-surfing. Nothiing to extreme, although I am virsatile and I would like to build a computer that can handle whatever I need it to. Do you really feel that the socket 775 is dead and that it would be impractical to invest in. I have purchased a ASUS P5Q Pro Turbo LGA 775 Intel P45 ATX Intel Motherboard that I have not taken out of the box yet. I have four(4) gigs of DDr2 memory, that I have used and would like to re-use. I am open to suggestions.

sell the board, keep the ddr2, the price is steadily rising

I have purchased a Intel Core 2 Duo E8400 Processor which I am about to change. Why would I want to buy Intel Core i7 920 Processor as opposed to simply Intel Core 2 Quad. between the Intel Core 2 Duo E8400 Processor BX80570E8400 - 3.0GHz, 6MB Cache, 1333MHz FSB, ant the Intel Core 2 Quad Q9550 Processor BX80569Q9550 - 2.83GHz, 12MB Cache, 1333MHz FSB, what is the performance difference and dose it justify the price difference.
I do nothing more than moderate gaming nothing extreme. Graphics to a certain extent and I do a lot of web-surfing. Nothiing to extreme, although I am versatile and I would like to build a computer that can handle whatever I need it to. Do you really feel that the socket 775 is dead and that it would be impractical to invest in. I have purchased a ASUS P5Q Pro Turbo LGA 775 Intel P45 ATX Intel Motherboard that I have not taken out of the box yet. I have four(4) gigs of DDr2 memory, that I have used and would like to re-use. I am open to suggestions.

LGA 775 truly is dieing/dead. i7 and i5 are totally worth the price increase compared to Core2Quad. TBH an overclocked C2Q will perform about the same as i7 in gaming on most GPU setups (up to 5970 or so, maybe a little higher) but it will last you much longer when graphics cards progress and the 1366 socket will have an upgrade path, where as 775 does not after the Q9650 (not including Extremes).

In everything else besides gaming i7 is simply in a class of its own. Now don't get me wrong, the i7 is a great gaming CPU, it is just pretty much overkill when paired with today's graphics cards. In the future we will see i7's true power in gaming (guess this is an 'imo').

If your budget does not ask for i5 or i7 then you should really look and see what AMD has to offer. You would have a better upgrade path with AM3 than LGA 775 for sure, and their price/performance ratio is unbeatable, especially in games.

Oh yeah, the performance difference between the E8400 and Q9550 depends on what you are doing. Quad core optimized games will show up to a 30% increase or so, this number will grow in the future. Honestly a VERY small amount of games see increase from quad core CPUs. Quad core optimized programs will sometimes show a 100% increase in performance. The E8400 will OC higher than the Q9550 due to a higher multiplier and only having 2 cores, which will keep the heat down.

If you can get all of your money back on the mobo and don't mind buying some DDR3 ram then go for i7 or i5.

For what you're using the computer for, I see no benefits in an upgrade to the Q9550. But if you're going to upgrade, then go for an i7, a new motherboard and DDR3 memory (you have no choice).

I'm running an E8400 in my gaming rig and a Q9550 in my workhorse rig and the only time the Quad shines is video encoding, other than that they are pretty much the same as far as general use goes and I can't see gaming being any better on the Quad but I can't test that for sure as my 680i board is not 45nm Quad friendly.

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helloeverybody how are you doing i a acer laptop 4315 i getting ready upgrade the cpu.
but first i need to update the bios to acer version 1.08? I need help i dont know how
to this. I also dont want get myself into something i cant get my self out of. I just try
to do it right the first time if at all possible?

go to acers site, they must have directions

Finally, someone talking some sense. For the OP's stated uses, your e8400 will do you quite well. Quads are nice, but not worth the upgrade price. Wait until (if ever) you need notably better performance. For surfing, that day may never come, for even moderate gaming, it might but then may also be handled by a GPU upgrade. To anticipate just about any single graphics card (all but HD5790), make sure you get a quality 500W-550W PSU. Look for full range active PFC (no little voltage switch) and at least 80+ certification. Antec, Corsair, PC Power & Cooling, Seasonic, and Enermax are among the better brands.

Anyway, you say you're about to change your processor. Why? If overall budget is the concern, then AMD pretty much owns the budget segment. A competent web surfer can be built for <$400. If there's a program you have listed that demands more performance, then Intel is your best choice. Something like an i7/860 on LGA1156 would be nice.

I agree.

If you own a MB that can use core 2 quads, just get a core 2 quad cpu. It will save you a lot of money by not having to upgrade everything.

The core i7's are nice cpu's but unless you do CAD or video editing/converting, you wouldn't use the the power of the i7 till many years down the road. Heck most programs right now cant even use 4 threads, yet alone 8.

Now if had a system like mine where i can only use intel p4 478 (where now i am forced to upgrade everything, when i do that is), then core i7 would be better as the c2d/q's are at there E.O.L.

Thank for your input.