Basic concepts
Central Processor
This part is also known as central processing unit or CPU, which in turn is made up by the control unit and the arithmetic and logic unit. Its functions consist in reading and writing the contents of the memory cells, to forward data between memory cells and special registers, and decode and execute the Instructions of a program. The processor has a series of memory cells which are used very often and thus, are part of the CPU.
These cells are known with the name of registers. A processor may have one or two dozens of these registers. The arithmetic and logic unit of the CPU realizes the operations related with numeric and symbolic calculations.
Typically these units only have capacity of performing very elemental operations such as, the addition and subtraction of two whole numbers, whole number multiplication and division, handling of the registers' bits and the comparison of the content of two registers. Personal computers can be classified by what is known as word size, this is, the quantity of bits which the processor can handle at a time.
Central Memory
It is a group of cells, fabricated with semi-conductors, used for general processes, such as the execution of programs and the storage of information for the operations. Each one of these cells may contain a numeric value and they have the property of being direction able. This is that they can distinguish one from another by means of a unique number or an address for each cell. The generic name of these memories is Random Access Memory or RAM.
The main disadvantage of this type of memory is that the integrated circuits lose the information they have stored when the electricity flow is interrupted. This was the reason for the creation of memories whose information is not lost when the system is turned off. These memories receive the name of Read Only Memory or ROM.
In order for the PC to process information, it is necessary that this information be in special cells called registers. The registers are groups of 8 or 16 flip-flops.
A flip-flop is a device capable of storing two levels of voltage, a low one, regularly 0.5 volts, and another one, commonly of 5 volts. The low level of energy in the flip-flop is interpreted as off or 0, and the high level as on or
- These states are usually known as bits, which are the smallest information unit in a computer.
A group of 16 bits is known as word; a word can be divided in groups of 8 bits called bytes, and the groups of 4 bits are called nibbles.
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