Hi dLTPN,

Optiplex 745 has three variants: Optiplex 745, Optiplex 745C and Optiplex 745 FLX. Intel Pentium 4 HT, Pentium D, Celeron D, Intel Core 2 processors are only tested with your computer by Dell. You can check the processors tested with Optiplex 745 in an image below:

Optiplex 745 support LGA775 socket. Q6600 Core 2 Quad processor supports the same socket. However, the max TDP of the same is 105W. This might work on your computer. For more information, you can check the comparison of both the processors from link: http://intel.ly/12TdMFh 

Dell does not offer processor or motherboard upgrades for purchase as discrete items, nor does Dell recommend upgrading the processor or motherboard in any given system. Therefore, Dell cannot support systems in which the motherboard or processor has been upgraded through third-party services or products. For more information, you can refer to the link: http://dell.to/TXOJja  

Please reply for further clarifications.

"Dell cannot support systems in which the motherboard or processor has been upgraded through third-party services or products. "

Chinmay S this is wrong.

Dell is not obligated to support anything that the system did not come with.

However TIE in conditions for warranty are not allowed.

There are three prohibitions under the Magnuson-Moss Act.

They involve implied warranties, so-called "tie-in sales" provisions, and deceptive or misleading statements.

This means that no matter how broad or narrow your written warranty is,

your customers always will receive the basic protection of the implied warranty of merchantability.

"Tie-In Sales" Provisions

Generally, tie-in sales provisions are not allowed. Such a provision would require a purchaser of the

warranted product to buy an item or service from a particular company to use with the warranted

product in order to be eligible to receive a remedy under the warranty.

The following are examples of prohibited tie-in sales provisions.

   In order to keep your Dell Computer warranty in effect, you must use genuine Dell Brand parts.

Failure to have scheduled maintenance or upgrades performed, at your expense, by Dell, Inc., voids this warranty.

While you cannot use a tie-in sales provision, your warranty need not cover use of replacement parts,

repairs, or maintenance that is inappropriate for your product.

http://www.dell.com/downloads/global/products/optix/en/opti_745techspecs.pdf

PROCESSOR

Intel® Core™ 2 Duo 1066MHz FSB Socket T with Dual Core technology  XD, EM64T, 2MB and up to 4MB L2 cache, EIST and VT (E6000 series)

Intel® Pentium® D 800MHz FSB Socket T with Dual Core technology  XD, EM64T, 2x2MB L2 cache,  EIST, and VT on 950/960 (900 series)  

Intel® Pentium® D 800MHz FSB Socket T with Dual Core technology  XD, EM64T, 2x1MB L2 cache  (800 series)

Intel® Pentium® 4 800MHz FSB Socket T with HT, XD, EM64T, and 1MB L2 cache  (500 series)

Intel® Celeron® D 533 MHz FSB Socket  T with XD and EM64T (300 series)

Hi dLTPN,

I agree with SpeedStep. My apologies for not putting it across as per the intended thoughts. Would like to rephrase that Dell does not recommend or offer processor upgrade but it is as your discretion in case you really wish to go  ahead with it. Warranty per say, issues arising due to the upgrade will not be covered under warranty , however we will continue providing support for other issues and parts. 

Please reply for further clarifications. 

I have an optiplex 745 (desktop) and, if i recall the processors correctly, managed to upgrade from a c2d e6400 (2.13 ghz) to a c2q q6600 (the 2.4 ghz c2q, think it is the q6600 but it might be the q6400).  To improve your chances, make sure you get the 95W TDP version of the q6600 (I believe the intel id is "SLACR" but you can check it at intels website) - there are actually two steppings of the c2q q6600's.  I imagine that the 105W would also work, but you might as well get the less power hungry chip as it is supposedly slightly better and I suspect more available (at least, most of the models I saw when shopping back when I was doing this were the 95W TDP models).  

Also, my understanding is that none of the 45nm c2q (or c2d) chips will work despite conforming to the socket, apparently due to BIOS limitations; make sure you stick with the 65nm chips (the q6600 is a 65nm chip).  However, I have never tried to install a 45nm chip so I might be wrong.

Also, make sure you get familiar with the process for upgrading the CPU, including cleaning up the heat sink and applying thermal paste to the new cpu.

You might need to update your BIOS in order to run the q6600, I am not sure as mine was fairly up to date and did not need an update.