Thanks for your help, i have 4 + 4 gb ram        
Hello I had a rx 460 to choose from, but unfortunately I could not find one for a reasonable price, so I decided on the gtx 645 OEM, the card works great for 9 years on the neck, but I have a problem with the ram, Only 8gb is not enough for me because I have quite a lot of applications that can consume up to 100%, so I would like to add ram even up to 12gb, I know that my motherboard supports 16gb, now the question is what is the ram, I know that I have ddr 3 and it is clocked at 1600 mhz, now the question is how to add this ram, for example 2x4gb, or 2x2gb also what input, because I'm not sure but the input is probably DIMM, ask how to fill up because I heard that the ddr3 memory can have various problems that the computer may not be able to do turn on when all slots are full. and also can I have a clock speed higher than 1600mhz, and do I need, for example, a RAM only from optiplex computers or any company. my computer is an optiplex 7020 MT   specification: i5 4590 8gb ram 256gb ssd drive graphics card: gtx 645 oem 290w power supply   if I didn't mention something, I'm sorry, but I've been interested in computers for quite a while, if something is not clear, I'm sorry, but I'm not very good at English   if you have any advice, I would be very grateful for your help   thank you in advance for your help
What ram can i put to optiplex 7020 MT?