Hard Drive memory (usually called “space” or “storage”) is where you store your saved files such as music, documents, and pictures. The average new computer these days will come with anywhere from 150 to 500GB of storage. One gigabyte (GB) is about 1000MB, and the average photo is around 1MB. The average song download is around 5MB.
RAM generally dictates how many programs you can comfortably have open at the same time, and the more RAM you have the faster your computer will feel while multi-tasking. Most new computers usually come with between one and four gigabytes of RAM.
To find out how much Hard Drive space you have available, highlight the Macintosh HD icon in the top right of your Desktop and press Command-I. If you have less than 5-10GB free it is time to look at deleting some files or adding some internal or external storage space.
To find out how much RAM you have installed, go to Apple menu -> About This Mac and look at Memory. If you have 1GB or less, you would benefit greatly from a RAM upgrade.