Computer Concepts A Brief Overview

Computer memory, known as primary memory, is closely associated with the central processing unit but is a separate component.

Primary memory is electronic memory without moving parts, allowing very fast access to data which is critical if the system is to keep up with the CPU.

Primary memory consists of two kinds:  random access memory (RAM) and read-only memory (ROM)

• RAM is read-write memory that can handle both data and instructions
• RAM is fast but volatile -- meaning that it only function while there is a stable power flow; any power interruption will erase its content -- when the power to the computer is turned off, contents of RAM disappears.
• RAM is not suitable for archiving purposes.
• ROM is read-only memory that typically contains the set of instructions needed to "boot" or start up the system when the power is turned on, e.g., Basic Input/Output System (BIOS).
• ROM contents are "burned in" to the chip and hence non-volatile -- without the ROM and its contents, the computer will not be able to start anew because the CPU will not know what to do.

Memory holds the data after it is input to the system and before it is processed; also, memory holds the data after it has been processed but before it has been released to the output device.

Memory also holds the programs needed by the central processing unit -- the stored program concept.

Memory is measured in bits or byte units as mentioned in the Introduction.

• Computer memory is partitioned (divided) into a number of data containers called memory cells
• Each cell stores a specific amount of data called a word (e.g., in our class, we will usually use examples using 8 bits.)
• Each cell has an associated location identifier called an address
• Data to be processed is coded in a binary (base-2 number) form using various encoding schemes discussed below:
• To begin with, digits 0 and 1 are binary digits and each is referred to as a bit for short.
• Again, 0 represents an OFF state and 1 represents an ON state
• Given nbits contained in a cell, there are 2ⁿ (read "2 to the power or n") ways in which zeros and ones can be arranged, e.g. given 2 binary digits (either 1 or 0), arrangements may be one of four (2² or 2x2 or 4) possibilities - 00, 01, 10 and 11.
• The capacity of a computer's memory is determined by the number of bits per cell and the number of cells into which memory has been partitioned, i.e., computer memory depends on how many bits may be stored in each cell and how many cells there are available.
• The industry settled on a sequence of 8-bits (given the unit name byte) as the basic unit of memory
• The term byte preceded by a prefix are used to express the memory/storage capacity of a computer. 

Units for Measuring Memory (Data Storage) Capacity: