Computer Memory

Computer memory can be viewed as a list of cells into which numbers can be placed or read. Each cell has a number of "direction" and can store a single number. The computer can be instructed to "put the number 123 in cell number 1357" or "add the number 1357 is in cell number is in cell 2468 and put the answer into cell 1595". The information stored in memory may represent practically anything. Letters, numbers, even computer instructions can be placed into memory with equal ease. Since the CPU does not differentiate between different types of information is the responsibility of software to make sense of what memory is no more than a series of numbers.

In almost all modern computers, each memory cell is configured to store binary numbers in groups of eight bits (called a byte). Each byte can represent 256 different numbers (2 ^ 8 = 256), from 0 to 255 or -128 to 127. To save more, several consecutive bytes may be used (usually two, four or eight). When negative numbers are required, are usually stored in two's complement notation. Other arrangements are possible, but not usually seen outside of specialized applications or historical contexts. A computer can store any kind of information in memory so it can be represented digitally. Modern computers have billions or even billions of bytes of memory.

The CPU contains a special set of memory cells called registers that can be read and written much faster than main memory area. There are generally two and 100 records depending on the CPU. The records are most frequently used data elements necessary to avoid the use of memory each time information is needed. Because the data is constantly being worked on, reducing the need to use the RAM (which is often slower than the ALU and control units) greatly increases the speed of your computer.

Computer's main memory are two principal varieties: random access memory or RAM and read-only memory or disk. RAM can be read and written at any time the commands of the CPU, but ROM is pre-loaded with data and software that never changes, so the CPU can only read. ROM is typically used to store your initial computer start-up instructions. In general, the contents of RAM is erased when you turn on the computer is off, but ROM keeps the data indefinitely. In the PC-ROM contains a specialized program called the BIOS that orchestrates loading the operating system on your hard disk into RAM when the computer is started or reset. In embedded computers, which often do not have disk drives, all the necessary software can be stored on disk. The software stored in ROM is often called firmware because it is computationally more that the hardware and software.

Flash memory blurs the distinction between ROM and RAM, as it retains its data when switched off, but is also rewritable. It is generally much slower than conventional ROM and RAM, however, its use is limited to applications where high speed is required.