The core duo and quad series simply doesn't run ddr3 1600 only ddr 3 1333 there is no way a proprietary 775 mobo from dell would be able to run it. The board would only support the max the cpu allows.
They made a mistake and are trying to blind you with science? All good fun! That it may run downclocked it might if it wasn't a dell but dell is proprietary they made the board in house to their own specs. not the general specs you'd normally find on most atx boards of that era. Memory density could be the exact issue as your g skill guy said.
Since memory probably depends on some microcode in the mobo bios probably similar to the cpu microcode to detect cpu it probably won't recognize anything later than it's release and pc3 12800/ddr3 1600 is later than pc3/ddr 3 1333.
How would it know to downclock a 12800 dimm? Or decide it could run 1.3v rather than 1.5v? There would have to be a logic circuit to determine that somewhere.
Also the 780 manual strictly specifies a 2gb limit, what logic would it have to say, oh this is a 4gb dimm and I can only use 2gb so I'll only use half of it? Doesn't exist. It won't recognize the dimm. and matched pairs of dimms to prevent any drop in performance. so mismatched dimms might work in some cases but not at full speed, that's the rules I understood from the book.
Everyone in the previous convo was having difficulty with 4gb with the 780 and one guy said he got 2x4gb dimms to run after he updated the bios to a15 that are 1.5v.
The problem in updating the bios is you'd need to load it from DOS and since the floppy disk retired there's no convenient way to exactly do that any more. Oh well the
bios page says it does boot off a DOS usb drive you can make one using
rufus. Windows 10 retired the boot to dos cmd prompt.
However his version was the 780, he didn't specify if was a 780 MT so probably it's a different mobo and the 2gb limit doesn't apply. The bios has to decide something like if not this then that and it's programmed in at the factory and the specs will fixed to what they decided at the time.
Or well someone's getting mixed up here as I found 2 data sheets one says the 780 has the ddr3 10600 1333 fsb and the other says the 780 MT has the ddr 2 1066 fsb. That means it has the 2 ddr2 dimms as standard but the manual says it could run the ddr 3 1333/ pc3 10600 in 4x2gb layout.
e7600 version with 1066fsb (the 2x2 ddr 2 dimms)
8400 version with 1333fsb (that should support 4gb dimms?)
There are two models with the same model number with the core 2 due 8400 version saying installed ram size 4gb and the e7600 version saying installed ram size 2gb.
And there are two 780 manuals with different titles that I downloaded... one says 780 tech guide book and one says 780 service manual. The 780 service manual says, 4gb limit, the 780 tech guidebook says 2gb limit.
So we have to do a bit more work to identify which 780 you have exactly. They are both mid towers the only thing I can find on the cnet site is a model number 468-9822 for the duo 8400 version and model number that I'm starting to think shouldn't have the 2gb limit when the bios is updated.
Going with the proprietary board theory though
The socket is oriented 45 degrees compared to most other 775 boards
It is different somehow in some way probably right down to every component they used in manufacturing. Somewhere in there is a logic that says 'I don't like dimms'.
So, my conclusion is that based on the
spotty info where the last guy says
https://www.crucial.com/usa/en/ct51264bd160b
worked in 4x4gb config
he bought the pc from ebay around 2016 second hand but doesn't say what version of the bios was installed. And that he tried 4 different brands of memory, and the first guy said he tried 3 different brands none of which worked.
What his definition of working no problem is, couldn't say. It wasn't running at pc3 12800 and there's no way to know if it was even running at pc3 10600. Maybe the system down clocked it to 600mhz or something. How would we know? It could see 16gb but at what speed? and something was timing out the display driver?
The story goes along the lines of people maybe trying to upgrade the memory with or without the bios update and having compatibility problems either way. And someone in the middle also chucks in the idea of the 2gb limit.
And there is a
third 780 optiplex manual saying 4gb limit with the title tech guide same as the 2gb limit version. Something happened way back when. Dell.
So the gist of it was the 4gb modules giving them grief anyway. They seemed to be keep trying 12800 dimms when the cpu only supports 10600 dimms max anyway so maybe ultimately with the a15 bios update there isn't any actual problem with 4gb 10600 dimms after all.
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