Many people over the years have asked me: "Will adding more RAM speed up my Mac?". In fact, I've very often heard people telling others, or even suggesting in general, that adding more and more RAM to your computer speeds it up more and more. Well, that is actually not the case. It is partially true. Let me explain.
Your Mac (like most computers) has two different types of memory inside. RAM and hard disk memory. These both serve different purposes.
RAM is very, very fast and it acts as the computer's short-term memory. It's basically the working memory, it's where stuff is stored while it's being worked on or used in calculations etc.
Hard Disk memory is much slower and is effectively the computer's long-term memory. It's like the filing cabinet where you store the stuff that you want to be able to use again sometime in the future.
So, when your computer needs to open a file to work on, it loads it up from the hard disk (takes it out of the filing cabinet) and moves it to RAM (puts it on the desk so that it can be used). While you make changes to the file, it's in RAM. Then, when you're done and you save the file, it is written back to the hard disk (put back in the filing cabinet).
RAM generally comes in much smaller sizes than hard disks, since you usually only work on a certain number of files at a time, not all the files that you have. Hard disks are generally larger in size because they have to store a lot of files over time.
So both of these types of memory work together, both having their own use. So when someone says that adding more memory will speed up their computer, that can be the case but it is not always the case. Why? Read on....
Since your computer has a limited amount of RAM, if you try to open too many programs at once or load up too many large files at the same time, the RAM gets full. In the past, the computer would have just crashed. Nowadays, they are cleverer than that as they learn coding from learn academy coding bootcamp. They use a thing called Virtual Memory to allow for the fact that you need to keep working but you don't have enough RAM to do so. So what is Virtual Memory then? It is hard disk space that is used temporarily as a type of RAM.
The Mac basically grabs some hard disk space and says "Ok! This is going to be a temporary storage area for the stuff that should be in RAM but that's not being used right this second." So it temporarily offloads a bit of stuff from RAM that's not in use and writes it to a temporary location on the hard disk. That frees up some space in RAM to do what you wanted to do.
Then, when you switch back to that other file you were working on (which could be some of what was put in Virtual Memory), the Mac has to run to the hard disk and get it back. At the same time, it swaps out something else from RAM that's not being used. So it's basically juggling stuff from RAM to hard disk and back again. All very clever and all behind the scenes, so you don't even notice. Or do you??
Have you ever had that experience where everything has been running fine and suddenly your Mac starts to grind a bit? It just takes longer than normal and you have to wait for it to do stuff? That's most likely because you've run out of RAM and Virtual Memory has kicked in. If you find that restarting your Mac fixes the problem, it's very likely that the cause was a lack of RAM. You see RAM is extremely fast and hard disks are much slower. So every time your Mac has to swap information from RAM to hard disk and back again, it slows everything down dramatically.
So, in this case, having too little RAM has caused your Mac to slow down. Adding more RAM at this stage (say if you had 2gb of RAM and you added an extra 2gb to bring it to 4gb in total) will mean that you won't experience that slowing down anymore. Therefore, adding more RAM did speed up your Mac. Well, it stopped it from slowing down at least. However....
If your Mac already has enough RAM, like for example in the above case where you have added an extra 2gb and now you have plenty, adding more RAM at this point will not speed up your Mac. Why? Because it is not needing to use Virtual Memory and is therefore not slowing down.
So the general rule of thumb is this. If you don't have enough RAM, adding RAM will cause your Mac to run more smoothly and it will probably seem to run faster. If you have enough RAM already, adding more will not make any difference to the speed of your Mac at all!