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Help Understanding Dual Channel Memory
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CliffyK View Drop Down
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Joined: 31 May 2024
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    Posted: 31 May 2024 at 9:06am
Hello all, new member here.

I just replaced an old Asus M5A78L-M_LX mobo in my 15 y.o. home-built workstation with an ASRock 970m Pro3--I re-used my AMD FX-8350 CPU. Video is handled by a GEForce GT-740

I installed four (4) new 8 GB DDR3 1600MHz RAM modules thinking this would provide 32 GB for my primary boot Linux Mint 21.3 system, however I find that while Linux sees all 4 modules (acknowledging 32 GB "on the mobo") only 16 GB is "available" to the o/s?

The mobo BIOS sees all four 8GB "sticks", I have shuffled them about in the slots with no change?

Booting to Win 10 (dual boot setup) revealed Windows had the same perspective; 32 GB installed, 16 GB "available"?

I also did a new installation of Mint 21.3 to another drive (same machine) and found it too only recognized 16 GB "available" memory

Is this a "dual-channel" memory issue? Would two (2) 16 GB modules in slots A-1 and B-1 (or A-2 and B-2) provide the 32 GB available to the o/s that I seek?

TIA,

-cliff-

BTW, the new mobo booted right up with no other issues!
    
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Additional info:

I pulled the memory from slots A-2 and B-2, leaving A-1 and B-1 both populated with 8 GB sticks. BIOS saw both, but indicated "Single Channel Mode".

Linux and Win10 both reported 16 GB installed but only 8 GB available to the o/s? Put in all four sticks and was back to where I was (32 GB installed, 16 GB available to the o/s); BIOS still says "Single Channel Mode", with all four slots loaded--is the mobo bad?

IF I get ambitious I will try slots A-2/B-2 loaded and just A-1/B-1 loaded...
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Points: 23993 		Post Options Post Options   Thanks (0) Thanks(0)   Quote Xaltar Quote  Post ReplyReply Direct Link To This Post Posted: 02 Jun 2024 at 7:04am
Try each stick on it's own, typically that issue happens when you have a bad module.
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Thank you for your reply! After trying every possible combination of modules (including "one-at-a-time", I'm pretty sure I have found the problem, am going to wait 'til I'm 100% sure to followup.

After the great memory swap I pulled the CPU and found it was missing a pin on the outer row 45° "opposite" the "triangle"--looking at my old mobo I found the pin stuck in the socket where it had been living happily for 12 years prior to my disturbing it. Odd that the CPU almost fell out when I removed it and that it would be a pin that did not disable the CPU entirely--it works fine other than no dual-channel memory mode.

Got a "new-to-me" CPU from a trusted vendor on eBay coming in on Tuesday, hopefully that will solve the mystery.

I will come back here and mark the post as Solved if I'm good.

Again thank you for your reply!

-cliff-
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That would do it for sure. Sometimes you can get away with a missing pin, not all
are used for anything critical but more often than not, it causes issues.
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I have tried to find a "pin-out" diagram for the AMD3+ socket, with no luck--I did find there are 938 pins, so it was pretty close to a "1 in a 1000" chance I'd get the dual-channel pin...
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I found an AMD3 pin-out, on that socket it's a "Memory Channel B" clock signal--so that makes sense...
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Well, I got the "new-to-me" CPU from eBay--DOA, missing two pins; good vendor though, sent it back for refund...

Got another on order, again coming in on Tuesday--I will be sure to report back with an update...
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You can check youtube for pin repair tutorials/videos if you like, a fun little
side project given the CPU is basically useless anyway.
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Thank you for the suggestion, however I have Parkinson's making my replacing a CPU pin unlikely to succeed...
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