Computer memory refers to any device associate with or part of a computer that can store data or programs either temporarily or permanently. This information is represented in what is known as binary code, a sequence of 1's and 0's. Computer memory devices are made of integrated circuits with silicon-based transistors or capacitors. They basically work as switches with 'on' or 'off' states or positions which denotes the 1's and 0's of the binary code or store information as charges. There are generally two types of computer memory; one is called primary storage and the other is secondary.
- Primary storage. Primary storage memory devices usually need to be powered with electricity in order to retain information. Thus they are also called volatile memory. Data stored in such devices can be retrieved at a constant time rate irregardless of where it is physically located. This form of storing data is known as random access memory (RAM).
- RAM. RAM is further broken down into two categories; static random access memory (SRAM) and dynamic random access memory (DRAM). The main difference between the two is the use of a process known as memory refreshing wherein stored data is read from a location and immediately rewritten in the same location. SRAM, unlike DRAM does not need to undergo memory refresh. DRAM needs to be refreshed because it stores data as charges within a capacitor which naturally leaks the charges thus necessitating a constant rewriting.
- Memory structure. A computer has a hierarchy of memory devices. It starts with the central processing unit (CPU) registers. The next levels are the internal and external caches (L1, L2 and L3) which are like temporary storage facilities that duplicate data written elsewhere thus shortening the time for access and transfer. Then comes DRAM which refers to the removable modules on the motherboard (and what is frequently and mistakenly referred to in layman terms as simply RAM). Then finally there is virtual memory which is a dedicated small space in the hard disk that works as a storage backup for DRAM. All these levels of memory actually operate in RAM fashion. Some like the caches are static and others like the DRAM modules are dynamic.
- DRAM. The easiest way to enhance a computer's memory is to upgrade its DRAM modules. Two of the most common types of these modules are known as SDRAM which means Synchronous DRAM and DDR SDRAM or Double Data Rate Synchronous DRAM. The later is much faster in processing data but the more important distinction is its physical difference. SDRAM uses 168 pins (the connecting surface to the motherboard) while DDR SDRAM uses 184 pins. So it is not possible to upgrade a computer with a motherboard that supports SDRAM by plugging in a DDR SDRAM module because it won't fit.
- Secondary storage. Secondary storage computer memory devices are also known as persistent memory or non-volatile memory devices. Unlike primary storage devices, they can retain information even when they aren't powered. Hard disks, optical disks and floppy disks all belong in this category. These devices also do not strictly operate in random access fashion which means that the speed of recovering data is affected by the physical location of the data. That is why such devices have speed specifications (typically revolutions per minute or rpm) to indicate how fast it can physically rotate and pinpoint the data's location.
The basic function of computers is to store, retrieve and process data. Thus memory is the operating principle behind all computing machines. But other sophisticated appliances nowadays also use memory or data storing devices to enhance their functionality.