That sounds like an interesting possibility..  I put the D 945 into my "dead" shuttle to confirm CPU or mobo, it was the CPU.  But even the Shuttle's fan cycles (which it didn't when it had an E8500 Core 2 Duo)... whcih makes sense when I compare the specs.  The D945 is a 95W processor, the Core 2 Duo is only 65W.  Now if the prices for the Core 2's would come down to under $20 :emotion-1:.

You can't put a core 2 ANYTHING into a GX620.  Its not going to work. I have seen inexpensive Smitfield /Pressler Pentium D's on Ebay/Amazon

Intel Cpu Pentium D 945 3.4Ghz Fsb800Mhz 2Mbx2 Lga775 Dual Core Tray

Intel - P-D 3.4GHz/4M/800 Dual Core CPU SL9QQ 

6 used from $12.00

Intel® Pentium® D Processor 960
(4M Cache, 3.60 GHz, 800 MHz FSB)     130 W 
Intel® Pentium® D Processor 950
(4M Cache, 3.40 GHz, 800 MHz FSB)     130 W
Intel® Pentium® D Processor 945
(4M Cache, 3.40 GHz, 800 MHz FSB)     095 W
Intel® Pentium® D Processor 940
(4M Cache, 3.20 GHz, 800 MHz FSB)     130 W
Intel® Pentium® D Processor 935
(4M Cache, 3.20 GHz, 800 MHz FSB)     095 W
Intel® Pentium® D Processor 930
(4M Cache, 3.00 GHz, 800 MHz FSB)     095 W
Intel® Pentium® D Processor 925
(4M Cache, 3.00 GHz, 800 MHz FSB)     095 W
Intel® Pentium® D Processor 920
(4M Cache, 2.80 GHz, 800 MHz FSB)     095 W
Intel® Pentium® D Processor 915
(4M Cache, 2.80 GHz, 800 MHz FSB)     095 W

Select     Intel® Pentium® D Processor 840
(2M Cache, 3.20 GHz, 800 MHz FSB)    130 W
Select     Intel® Pentium® D Processor 830
(2M Cache, 3.00 GHz, 800 MHz FSB)    130 W
Select     Intel® Pentium® D Processor 820
(2M Cache, 2.80 GHz, 800 MHz FSB)    095 W
Select     Intel® Pentium® D Processor 805
(2M Cache, 2.66 GHz, 533 MHz FSB)    095 W

That sounds like an interesting possibility..  I put the D 945 into my "dead" shuttle to confirm CPU or mobo, it was the CPU.  But even the Shuttle's fan cycles (which it didn't when it had an E8500 Core 2 Duo)... whcih makes sense when I compare the specs.  The D945 is a 95W processor, the Core 2 Duo is only 65W.  Now if the prices for the Core 2's would come down to under $20 :emotion-1:.

SpeedStep and rdunnill - I agree, the core 2 duo can't work in the GX620, was wishing :>)  I am hoping for an inexpensive Core 2 Duo to bring my shuttle back up to useable status without spending much money.  The GX620 doesn't have enough oomph to work as my HTPC without the Pentium D 945, but that makes it too loud :>(

Intel® Core™2 Extreme Processor QX6800 (8M Cache, 2.93 GHz, 1066 MHz FSB)

for detail http://ark.intel.com/products/30720

its best processor for DELL  Optiplex GX620 because Optiplex GX620 use

more chipset detail http://ark.intel.com/products/27720/Intel-82945G-Memory-Controller 

@QaziShahbaz: have you try it? Or you just follow chipset rules?

Chipset rules do not apply to Dell. Upgrades depend on BIOS, and only Dell knows full capabilities in terms of processor upgrade.

Please do not advise if you did not try it, if you tried it, please upload CPUID screenshot!

No one's proven Speedstep wrong on this issue. The GX620 was marketed just prior to the Core series release, and it's doubtful that Dell retrofitted the BIOS to accommodate the then-cutting edge CPUs.

rdunnill, don't pay attention to this post, poster just joined Community to post this? Until someone will provide any screen shots to prove miracle, it would be still a myth.

I wish it could be the true, but I have wishful thinking as you all know.

No one's proven Speedstep wrong on this issue.

The GX620 was marketed just prior to the Core series release, and it's doubtful that Dell retrofitted the BIOS to accommodate the then-cutting edge CPUs.

Based on the information in this thread and others, I successfully upgraded my GX620's 3.2 GHz Pentium 4 to a 3.6 GHz Pentium D.  The steps were as follows.

• Upgrade BIOS to A11 (for an easy way to do this on Ubuntu, see http://thoughtsdaily.wordpress.com/2011/11/01/update-dell-bios-in-ubuntu/)
• 130W Pentium D960 from eBay ($45)
• J9761 heatsink from eBay ($20)

Upgrade went smoothly and there's been no cycling or high-speed running of the fan as some others have reported.

This is an Ubuntu machine running slimserver, backup, VPN and some other apps for a home network.  It's also running virtualbox with a WinXP guest.  The main reason for the upgrade was to improve the performance of the WinXP guest; it's noticeably snappier with the upgrade.

Well, this is 2013. You spent $65 for a CPU upgrade on GX620. Good effort but really not worth it in my humble opinion.

Pentium D by nature was not a well designed/efficient processor which was built on two power-thirsty Pentium 4s back to back.

Core 2 was an entirely new line, much faster and greener.

A refurbished Lenovo ThinkCentre M57 (Core 2 Duo E6550 2GB/80GB SFF) can be had for the same price on Ebay today.

http://www.ebay.com/sch/i.html?_nkw=lenovo+m57

[quote user="rdunnill"] No one's proven Speedstep wrong on this issue. The GX620 was marketed just prior to the Core series release, and it's doubtful that Dell retrofitted the BIOS to accommodate the then-cutting edge CPUs.

rdunnill, don't pay attention to this post, poster just joined Community to post this? Until someone will provide any screen shots to prove miracle, it would be still a myth.

I wish it could be the true, but I have wishful thinking as you all know.

[/quote]

For giggles, I tried installing a Core 2 Duo E6300 in my GX620. It didn't boot.

Kisianik dell optiplex gx 620 support the pentium serious i check it on my computer pentium d 960 with is 3.6Ghz/800Mhz/2*2MB and also support pentium extreme processors with HT technology 

Intel® Core™2 Extreme Processor QX6800 (8M Cache, 2.93 GHz, 1066 MHz FSB) for detail http://ark.intel.com/products/30720 its best processor for DELL  Optiplex GX620 because Optiplex GX620 use Intel® 945G Express Chipset with Max Supported FSBs 1066MHz more chipset detail http://ark.intel.com/products/27720/Intel-82945G-Memory-Controller

Compare this to the one below - you are confused I can see this.

Kisianik dell optiplex gx 620 support the pentium serious i check it on my computer pentium d 960 with is 3.6Ghz/800Mhz/2*2MB and also support pentium extreme processors with HT technology

I see no similarities between Pentium D and QX CPU, at least for GX620 application,I know for long time that Pentium D is the best you can get, so noting is new here....

.

dell OptiPlex gx620 only have PLGA775, but Intel® Core™2 Extreme Processor QX6800 support only LGA775 socket so Intel Pentium extreme edition processors only the best uP ever for dell OptiPlex gx620.