Dell Optiplex 780 mt ram upgrade

That's fine if you able to mix RAM brands and it works.  Not all Dell's are like that.  We've had the instances in this forum whereas mixed RAM wasn't working.  Fireberd (Rockstar), besides his Dell laptop, has a homebuilt Asus.  It won't take mixed RAM, but will take either brand he has separately.  This isn't just a horror tale.

It might be the Dell's that are older than your 790 that are finicky like that.  @donm4599x - I do like your advice on price comparison.  EBay, Walmart.com, Amazon, and Newegg are just a few good places to do that

While I remember, Kingston Value Ram (KVR) rarely works in Dell's.  Regular Kingston does.

There is a lot of memory horror tales told around dell campfires. Mostly false.

I have a 790. I am running 3 different brands of ddr3 memory. I have hynix, adata and kingston. Two of these sticks are also the forbidden 8 GB modules, not endorsed in any official dell scriptures. My computer has 24 GB, running in dual channel mode. I tested with memtest86, no problems.

The memory controller is on the intel cpu chip, It's not on a special crippled chip made by dell. They don't make any integrated circuits ... They are a system integrator and marketing operation. Everything is contracted out to other companies who make the boards and other components. Dell does a pretty good job at everything except for the poor technical documentation and lack of transparency.

I wouldn't pay more than 7 - $8 for 4 GB ddr3 memory modules.  I bought two 4GB hynix modules for $14. I bought two 8 GB modules for about $15 each. Total is 24 GB.

Before you buy this machine from your friend, check online to see what these old machines are selling for.

You may be able to get a better machine for the same amount.

The Ram I can get for $26 is on Amazon.ca and since I plan to install the Core 2 Quad Q9550 it will have new paste put on it since it's only a Core 2 Duo in it now the GPU is I plan to put in it is the one that I have in my 11 year old HP desktop the MSI GeForce 210 1GB I have a ASUS 24X DVD burner in the older HP that will go in the Dell same with a Samsung EVO 860 500GB SSD also a D-Link AC1200 PCIe wireless card. My friend offered this computer for free to help me out where my HP desktop is working but having slow DDR2 ram it's not the fastest computer and it don't like hard drives over 500GB I have a 4TB external hard drive I can't use on this old HP but yet I have another 4TB external hard drive that works fine weird but it's only showing the hard drives as only being 500GB not 4TB in the BIOS but showing the full size through Windows 10 I was told it's cause this computer being so old it don't really support anything bigger then 500GB so I hope the Dell will support the bigger external hard drive with out problems or should I install the hard drive internal? I am wondering what's the difference between the Core 2 Quad Q9550 and the Core 2 Quad Q9650 will I see enough difference in performance to make it worth spending $60 on Ebay.ca 

According to game-debate, the difference between the 2 CPU's you mention is a 4% performance increase, 2.83GHz vs. 3.0GHz.  It's unlikely you'll notice any difference.  https://www.game-debate.com/cpu/index.php?pid=23&pid2=18&compare=core-2-quad-q9550-2-83ghz-vs-core-2-quad-q9650-3-0ghz 

Crucial.com is a good place to check for compatible SSD's.  https://www.crucial.com/usa/en/compatible-upgrade-for/Dell/optiplex-780-mini-tower  Up to 2TB SSD's can go in the 780.  You'd have to ask Crucial if you can use 2 of those, which I think is possible.

As for what the 780 can take for external SSD's, I'll have to let one of our other experts answer.  I don't know if there's a size limit.

Not an expert, but I think external drives have a sata to USB converter circuit, and that may determine the max disk size. When buying an external enclosure, make sure it can handle the drive size you plan on using. The ones I have seen on ebay and the like usually specify max size.

For internal drives, you can set them up as GPT rather than MBR, and there's no practical limit on size. However, such drives cannot be used as boot devices, unless you have UEFI instead of legacy bios.

My reply disappeared that was weird anyway I have the 4TB in a cheap USB 2.0 case I got from China and it didn't say much in the listing it's very cheap looking. I plan to instill it internal so the case won't be needed. I have found a site that you can use to find what ram is supported in your computer all you need to do is select your brand and model and it will tell you all the ram that's supported. I won't go and buy the Q9650 for only a 4% gain it's not worth the $60 price tag but if the the one I have now the Q9550 don't work and I have to replace it then I may spend another $20 some to get the better one. I have planed to buy a GPU for this computer I have picked out this one MSI GeForce GT 710 DirectX 12 and I have picked out this power supply CORSAIR CX Series CX450 450W ATX12V 80 PLUS BRONZE Certified Active PFC by watching Youtube videos and doing a search on the motherboards the Dell 780's have the MT looks to have the normal ATX 24 pin motherboard power supply connector while the SFF version has the mini power supply connector on the motherboard. Also it seems like the MT is the best version to get when it comes to upgrading.

https://www.neweggbusiness.com/Find-IT/memory-product-finder#/

I wasn't able to order the ram I wanted it was sold out but I was able to order this it shows on the Newegg site I already posted here as supported what I am wondering will this ram really work on the Dell 780 mt? I have ordered 2 sets already to max it out. Also what's this brand of ram like? I'm worried I just wasted my money since I got no extra money to send the ram back.

CORSAIR Vengeance LP 8GB (2 x 4GB) 240-Pin DDR3 SDRAM DDR3 1600 (PC3 12800) Low Profile Desktop Memory Model CML8GX3M2A1600C9

Specific Low Density INTEL ram works fine with the 780.  INTEL Q45 chipset DDR3

https://www.crucial.com/usa/en/optiplex-780-desktop/CT2367680

DDR3 PC3-12800 • CL=11 • Unbuffered • NON-ECC • DDR3-1600 • 1.35V • 512Meg x 64 •