HP Compaq dc7900 Ultra-slim Desktop PC CPU Compatibility

[NonSequitur777]

Dear Forum, by chance I read a 4-year old exchange related to the CPU compatibility of the HP dc7900 USDT.  It so happened that I had one, powered by a measly E8400 with 2gb of DDR2 RAM -ready to be scrapped, I should add.  However, the claim was made that, quote: "Highly doubtful the Q9550S would work at all, because it is not supported for any model in the series, and there probably isn't a microcode update for it that would allow it to work without a microcode error report at each boot."

Well, I looked into the dc7900 USDT specs, and thought the Q9550S should work just fine.  Bought one cheaply through AliExpress, and indeed, the Quad did work (see attachments). Just because it now became "a project", I bought two 4GB dual-channel DDR2-800 RAM sticks, added a SSD, a bigger plug-in power supply, and bypassed the onboard graphics with a GT 730 2GB graphics card -plugged in outside the chassis through the PCIe Mini Card slot. Because the PC's performance exceeded my expectations, a GTX 1050ti 4GB card is on the way. Also changed the original CPU two-pipe heat sink with a dc7800 three-pipe heat sink, upgraded the cooling fan, and replaced the 1600x900 monitor for a 1920x1080 screen.

Waiting for a Xeon E5450 (3.00 Ghz Quad Core LGA771, modded for LGA775) -will do my best to make this one work, too.

Stay tuned.

[NonSequitur777]

Also ordered a Xeon X3370 (12M cache, 3.00GHz, 1333 MHz FSB, SLB8Z, LGA775) and see if this quad-core will work too on the HP dc7900 USDT.  Since these processors are now available very cheaply, it won't break the bank.

[NonSequitur777]

Dang.  Was unable to get the Xeon X3370 to work yet ("1802 - Processor not supported This system board does not support this processor"). Found thus out that CPU compatibility entails more than just using the same LGA775 socket. Indeed, OEM (Original Equipment Manufacturer) computers are generally less cooperative in these matters. Will continue to research (see, for example: https://www.delidded.com/lga-771-to-775-adapter/3/

and: https://www.bios-mods.com/forum/Thread-Microcode-Update-for-HP-Compaq-DC7900-786G1-to-support-Q6600-... )

I did update the dc7900 USDT BIOS to the newest and last (2015) version: 786G1 v01.27, by USB flashing. This most current version had to be flashed because the standard procedure (sp73584.exe > "Run as administrator") didn't work.

Follow these instructions as submitted by Neill_R two years ago to update BIOS without accessing your OS: https://h30434.www3.hp.com/t5/Desktop-Operating-Systems-and-Recovery/Questions-on-BIOS/m-p/7105716  The flash drive should contain files such as 7G1_0127.bin, which can be found on the C: drive > swsetup > SP73584 in the "DOS Flash" sub folder.

[NonSequitur777]

The Xeon E5450 (3.00 Ghz Quad Core LGA771, modded for LGA775) did not work either.  No screen activity whatsoever, only response was that the heat sink fan ramped up.  Back to the Q9550S -started right up.

Got a good deal on a Q9650 (2M Cache, 3.00 GHz, 1333 MHz FSB, LGA775), and is supposed to show up some time next week.  Only problem is its TDP (Thermal Design Power), which is listed at 95W.  According to HP, the HP dc7900 USDT only accepts CPU's up to 65W.  We'll see.  As mentioned earlier, I replaced the original 19.5/135W power supply with a robust 19.5V/230W power supply, and the NVIDIA GT 730 graphics card is powered separately through an EVGA 460 BP power supply, so motherboard power restraints shouldn't be an issue.

[NonSequitur777]

The ordered "Intel CORE 2 Quad inside" sticker came in, and replaced the now obsolete "Core 2 Duo" on top of the newly metallic-red spray painted upper access panel. Also replaced the PCIe riser card used for the GT 730 graphics card with a higher quality version ("TISHRIC PCIe x16 Riser 009S Plus Video Card") through AliExpress. It has double (8) the solid capacitors, and more importantly, 2 x 6-pin power sockets, very helpful to power more demanding graphics cards such as the GTX 1050ti 4GB, that I am waiting for to arrive.

[NonSequitur777]

The Intel Core 2 Quad Q9650 showed up today, and I tried it out.  Unfortunately, the dc7900 USDT did not support it: "1802 - Processor Not Supported This system board does not support this processor."

I was hopeful the Q9650 would work because this CPU shares many similarities with the Quad that does work on the dc7900 USDT, the Q9550S, such as the same Core Stepping (E0) and CPUID (1067A).  The last picture shows the Q9550S "CPUID Information".

The Q9650 is likely not supported because it exceeds the PC's programmed 65W TDP.

I am sure HP could fix this with a BIOS/micro code update if they were so inclined.

Anyone?

[NonSequitur777]

Update: Took some trial & error, but was able to nicely fine-tune the dc7900 USDT's video graphics/memory & Q9550S capabilities. Can now actually play games such as Call of Duty Modern Warfare 3 very decently.

Here's a link with helpful information to tweak your RAM allocation memory: https://support.robertsspaceindustries.com/hc/en-us/articles/360000083387-Out-of-memory-errors-set-y...

Specifically, scroll down to "Set a Specific Pagefile Amount".  For number 7 ("Click Custom and enter a size range. For example with 16GB, you may want to enter Initial Size of 8000 MB and Maximum size of 12000 MB."), since the max installed DDR2 RAM for the dc7900 USDT is 8GB (2x4GB), I set the initial size at 4000 MB and the maximum size at 6000 MB, which produced excellent results, and fixed the "out of memory" errors dead in its track.

In addition, the next link also helped me to fix certain video memory issues. This "Large Aware Address" download is an application that assists in allowing games to utilize more than 2GB of RAM. Lots of games pass the 2GB limit (usually after 15-20 minutes of game play) and consequently the game's engine can't handle it and crashes. This is fixed with Large Address Aware, which allows games to exceed the 2GB boundary.

Link: https://www.techpowerup.com/forums/threads/large-address-aware.112556/

[NonSequitur777 · Accepted solution]

Out of 89 HP dc7900 USDT PCs submitted for online benchmarking -see pic, my rig scored the best ("best" is relative, since this desktop model is antiquated and objectively under performs compared with newer PCs ).

It was interesting, but I'm done with this PC.  The Intel Q9550S is the fastest CPU this computer can accept, and the NVIDIA GTX 1050ti 4GB is about the fastest graphics card it can handle.  Btw, I am planning my next project to seriously max out an HP Compaq Elite 8300 USDT -where no one has gone before! Stay tuned, will start a new thread.

[NonSequitur777]

Connected a Radeon RX 570 4GB graphics card -Still highest ranked HP dc7900 USDT on Userbenchmark.com!