If a computer cannot find the data it needs in the L1, L.2 or L3 cache, the computer must get the data from the slower main memory, called RAM. The computer places a copy of the most commonly requested data from RAM in the memory cache. This process constantly updates the memory cache so it always contains the most recent and most often used data. Accessing RAM is usually about half as fast as accessing L3 cache.

Using memory cache is similar to working with documents in your office. When you need information, you look for information in a specific, logical order. Each step along the way takes up more of your valuable time.

A bus is an electronic pathway that carries information between devices in a computer.

Bus width is similar to the number of lanes on a highway. Larger bus widths can transfer more data along the bus at a time. Most types of buses measure the bus width in bits, such as 32 or 64 bits. Some types of buses measure the bus width in the number of lanes, such as 32 lanes.

Bus speed is similar to the speed limit on a highway. The higher the bus speed, the faster data travels along the bus. Bus speed is measured in megahertz (MHz), which is millions of cycles per second, or gigahertz (GHz), which is billions of cycles per second.