The Different Types of Computer Memory
Computer memory refers to the hardware, or physical devices, used to store sequences of instructions or data for use in a computer. This storage may be on a temporary or a permanent basis based on the type of memory. There are two types of computer memory: primary memory (i.e., RAM) and secondary memory (i.e., ROM). In addition, there is both virtual and protected memory which may occur within RAM and ROM. Memory is stored in binary on computer memory devices. Binary is a system of digits or bits expressed using two symbols: 0s and 1s. Eight bits, any combination of eight 0s and 1s, forms a symbol or character and is called a byte. These bytes are stored in computer memory.
RAM is random access memory, and it is the working memory of a computer. It is volatile, meaning that this memory is reset when the computer turns off. Most RAM is either Static RAM (SRAM) or dynamic RAM (DRAM). These two types of RAM differ in how long they retain their memory. SRAM retains its contents as long as the power to the computer is on, making it easy to interface. DRAM requires regular refresh cycles to prevent its contents from being lost, and it is much more complicated to interface and control.
ROM is read-only memory, and it is the permanent memory used to store programs and software required to perform functions on a computer such as starting programs and even booting up the operating system. Unlike RAM, ROM is non-volatile. This means that when the power to the computer is turned off, the contents of the memory are not lost. Instead, the contents of read-only memory are written at the time the computer was manufactured.
When an operating system controls all the physical memory, this is called virtual memory. So, if a program requires memory, it will request it from the operating system. The operating system on a computer will then decide what location to place or store the memory in. This allows for multiple types of memory to be used. For example, some memory can be stored in RAM while other memory is stored in ROM or on the computer's hard drive.
Protected memory enhances the security of a computer system by the way it allocates memory. Protected memory is actually a system where programs are given an allocation of memory and they are not permitted to go outside that range. If a program attempts to alter memory that does not belong to it, the operating system terminates the program. This way, it is only the single program that crashes, and no other program or the operating system itself is affected by the error.