The two key categories of storage as it relates to your computer are primary storage and secondary storage. Primary storage also goes by the names main storage, main memory or internal memory. Examples of primary storage in your computer are random access memory and cache memory. Your secondary storage is also known as auxiliary storage or external storage with your internal hard drive as the most common type of secondary storage.
Primary Storage vs. Secondary Storage
Internal to your computer, the primary storage gathers and holds your data and files on a temporary or short-term basis until it is no longer required. It is the fastest category of memory or storage devices. Your hard drive stores virtually all the programs and applications installed on your computer including the operating system, device drivers, applications and general user data. You may also have additional secondary storage devices connected to your computer -- an external hard drive, USB thumb drive or a media player such as Blue-ray or DVD.
Random Access Memory
RAM is considered the fastest storage and can achieve very high transfer rates of data. When programs or files are accessed, the data is temporarily loaded from your hard drive into your RAM where it can be smoothly accessed. However, if your RAM becomes filled, your operating system will adjust and send some of the open programs and files to your hard drive's paging file. This file is slower than your RAM because it resides on your hard drive and is one of the causes of your computer being unresponsive. For this reason, having enough RAM to handle all your work allows you to keep multiple programs open without any concerns with slowed down or unresponsive memory.
Cache memory is generally joined onto the motherboard and installed on the core processor or main RAM. It provides quicker access by storing an instance of the programs or data regularly accessed by the processor. With the information in cache memory, the processor does not need to go to RAM or the hard drive to get the data, it already has an instance of it in its memory. An example of this is using the Internet and a web browser. The cache will store the website's HTML, images and other information so that a page will load more rapidly after its first visit.
The processor register is local storage that holds data being processed by the core processor. It provides rapid access to the data and may include the address of the memory location instead of the real data. The register first identifies the data before it is manipulated by the core processor. An example is an arithmetic operation with two numbers, where the numbers, the inputs and the results are stored in the processor register.