Hi starduster31,

The 780 has an Intel Q45 chipset which supports the following CPUs: 

http://www.cpu-upgrade.com/mb-Intel_(chipsets)/Q45_Express.html

The highest spec of CPU that Dell shipped with the 780 was the Q9650 so anything from that list, up to and including the Q9650 should be fine. 

As far as the memory is concerned, it will take up to 16GB (4x4GB) of Non-ECC dual-channel 1066MHz or 1333MHz DDR3 SDRAM 

* To fully utilize 4GB or more of memory requires a 64-bit enabled processor and 64-bit operating system.

DELL™ OPTIPLEX™ 780  TECHNICAL GUIDEBOOK V2.0  Intel Q45 Express Chipset w / ICH10DO
Depends on which size you have MT  DT SFF USFF

Recommended Ram is VERY specific.  The spec says that 4 gigs is max for USFF but this is not correct.

https://www.amazon.com/Timetec-1600MHz-PC3L-12800-Unbuffered-Computer/dp/B00IV19IA8/

Timetec Hynix IC 8GB Kit (2x4GB) DDR3L 1600MHz PC3L-12800 Non ECC Unbuffered 1.35V/1.5V CL11 2Rx8 Dual Rank 240 Pin UDIMM

http://i.dell.com/sites/doccontent/business/solutions/engineering-docs/en/Documents/optiplex-780-tech-guide.pdf

The USFF has tiny power supply so it cannot use 95W or higher cpu's

Intel® Core™ 2 Quad Q9650/3.00GHz, 12M, 1333FSB
Intel® Core™ 2 Quad Q9550/2.83GHz, 12M, 1333FSB
Intel® Core™ 2 Quad Q9400/2.66GHz, 6M, 1333FSB
Intel® Core™ 2 Quad Q8400/2.66GHz, 4M, 1333FSB
Intel® Core™ 2 Quad Q8300/2.50GHz, 4M, 1333FSB

Don't be fooled by the Mhz Myth however.

Very little if any difference between these standard cpus

Intel® Core™ 2  Duo E8600/3.33GHz, 6M, 1333FSB
Intel® Core™ 2  Duo E8500/3.16GHz, 6M, 1333FSB
Intel® Core™ 2  Duo E8400/3.0GHz, 6M, 1333FSB
Intel® Core™ 2  Duo E7600/3.06GHz, 3M, 1066FSB
Intel® Core™ 2  Duo E7500/2.93GHz, 3M, 1066FSB

Supported CPU's

Sorry I took so long to answer, I really appreciate your suggestions. Is there a power supply that will fit inside the SFF case? It uses the 235W power supply that looks like an L in shape. Thanks again for all your help!!

so no nothing faster than core2 duo E8600 3.3GHz is possible in the optiplex 780 USFF?

this 780 USFF runs very cool now with new thermal compound .. is overclocking possible/advisable?

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http://i.dell.com/sites/doccontent/business/solutions/engineering-docs/en/Documents/optiplex-780-tech-guide.pdf

The USFF has tiny power supply so it cannot use 95W or higher cpu's

Intel® Core™ 2 Quad Q9650/3.00GHz, 12M, 1333FSB
Intel® Core™ 2 Quad Q9550/2.83GHz, 12M, 1333FSB
Intel® Core™ 2 Quad Q9400/2.66GHz, 6M, 1333FSB
Intel® Core™ 2 Quad Q8400/2.66GHz, 4M, 1333FSB
Intel® Core™ 2 Quad Q8300/2.50GHz, 4M, 1333FSB

 

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I'm thinking to replace the optiplex 780 USFF power supply (180W) with a power supply from the later generation optiplex 7010 (200W) .. it looks like exactly the same form factor .. would that be sufficient to run one of these LGA 775 quad core processors instead of E8600 dual core?  or is there better option using a 775 to 771 adapter?  

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I'm thinking to replace the optiplex 780 USFF power supply (180W) with a power supply from the later generation optiplex 7010 (200W) .. it looks like exactly the same form factor .. would that be sufficient to run one of these LGA 775 quad core processors instead of E8600 dual core?  or is there better option using a 775 to 771 adapter?  

this afternoon installed Q9650 quad core to replace the E8600 dual core ..  and working very well with previous upgrades of crucial 2 x 4GB (CT2K51264BD160B) and 200W power supply (200W PSU KG1G0 4GVWP L200EU-00 PS-3201-9DB).  

but the stock A14 firmware at first reported "Alert! Incompatible processor detected .. halted" .. so modified A15 firmware was required:

https://www.bios-mods.com/forum/Thread-Solved-Dell-Optiplex-780-Quad-Core-Support

https://www.dell.com/support/home/us/en/19/Drivers/DriversDetails?driverId=R257719

Hy, i also want to upgrade to a Q9650, do you still have the modifide a15 bios image, or plese explain how you medified it. I allready have a15 bios on it

THX in advance

Hi @b0gy,

You shouldn't need modified BIOS to run the Q9650.  May be at one time it was needed before more versions came out?  Not sure.

You should be able to update to the latest BIOS for your 780 using the Dell Support Assist site.  I use the Q9650 in my 755 with A22 BIOS.  Only the USFF model of the 780's can't take a Q9650.

Optiplex 780 Tech Guide

THX, mine is a Dell Optiplex 780 DT, it should work then. I will order it online and come back with a confirmation after i installed it .

Am also thinking of upgrading my i3 Dell Optiplex 780 mother board to i5  or i7 but am lost between whether i should changing the whole mother board or just changing the processor and ram.... What would be the best move to make here folks?