Computer Memory

Computer memory is the computer components, computer devices and external storage media that can be used to store data for a varying amount of time. It is also known as computer data storage or just storage or memory. It is the core function of all new computers and when coupled with the CPU (Central Processing Unit) forms the basic computer model that has been universally used since the 1940s.

Computer memory usually refers to the RAM (Random Access Memory) although there are four forms of memory; primary storage, secondary storage, tertiary storage and offline storage. Offline storage is a portable device that can store and transfer data from one computer to another.

Primary storage or memory or RAM is the only type of memory that can access the CPU. It is small and light but it is volatile which means that it can lose stored data when there is no power going to it. Therefore a non-volatile storage device is used in computers to run the computer because if it simply relied on the RAM, it would have no data to read from and therefore no instructions to start the computer when power is sent to it.

Secondary storage refers to the mass storage device, an example of which is the hard drive or hard disk. This is typically between 20 and 120GB. It is different from primary storage because it can’t be directly accessed by the CPU. It also non-volatile which means it doesn’t lose data when the device is turned off. Secondary memory is typically slower than primary storage but faster than tertiary or offline storage.

Tertiary storage or tertiary memory is used for archival of rarely accessed information. It is made up of a system where a robotic arm is used to mount and dismount a removable storage device into storage device. It is typically used for very large amounts of data such as tape libraries or optical jukeboxes. Tertiary storage can be used with human interaction.

There are many ways to characterise storage. One way is the volatility, which tells us if the storage device will keep or lose the data when it is not being supplied with electricity. Another way to characterise storage is it’s ability to access non-contiguous information. If it can access any location at any time, it is known as random access. Otherwise it is known as sequential access.

The capacity and performance of computer memory is particularly important for computer users. The two major factors are storage capacity and storage density. The storage capacity is the total amount of data that a storage device can hold in terms of bits or bytes. The storage density refers to how compactly the information on a storage device can be compressed.

Other important factors include the latency which is the time it takes for a particular location in the storage to be found. This is measured in nanoseconds, milliseconds or seconds depending on the type of storage as some devices are faster than others. The throughput is the rate at which information from the storage device can be read or written. This is usually measured in megabytes per second (MB/s) or bit rate. The read rate and write rate can be differentiated for both storage latency and storage throughput.