, otherwise known as RAM (random access memory), can be one of the easiest and most effective upgrades for your Macintosh computer. If you run a lot of applications at the same time, increasing the amount of memory can vastly improve performance. For most systems, upgrading the memory only takes a couple of minutes as the the memory slots are very accessible.
The hard drive
stores all of your information and data such as applications, photos, videos, music, and documents. A hard drive that is running low on disk space will reduce the overall performance of a system. In addition to having a large capacity hard drive, performance can also be increased with a solid state drive (SSD)
or hybrid drive (hard drive + SSD)
The processor, also known as the CPU (central processing unit) performs all of the calculations for the computer. Increasing the speed of the CPU has a high correlation to the speed in which applications can carry out their processing needs. Memory will help when multiple applications are running at the same time but the CPU will govern how quickly each application completes its task.
The video card
helps with the quality of graphics for the computer. Upgrading to a good video card can greatly improve video editing and games on your Mac.