Central Processing Unit:
Computer’s brain
Tharindu Weerasinghe Computer Engineer
What is the governing element of the human body? In other words what
helps you to manage your processing duties? It is the BRAIN. Brain is
the central processing unit of all animals, same goes for computers.
Human beings are more powerful than all the other animals because human
beings have a brilliant processing power. Similarly computers which have
powerful processing power (advanced CPUs) are very effective and
efficient than the computers which have less powerful CPUs.
A Central Processing Unit |
CPU is the controlling centre of the computer that converts data
input to information output. This control centre, called the Central
Processing Unit (CPU), is a highly complex, extensive set of electronic
circuitry that executes stored program instructions. All computers,
large and small, must have a central processing unit.
The Central Processing Unit consists of two parts: The control unit
(CU) and the arithmetic-logic unit (ALU). Each part has a specific
function.
Control Unit (CU)
Control unit of the CPU has the electronic circuitry that uses
electrical signals to direct the entire computer system to carry out,
execute stored program instructions. Like a typical leader of a team,
the control unit does not execute program instructions; rather, it
directs other parts of the system to do so. The control unit must
communicate with both the arithmetic-logic unit and memory.
Arithmetic-Logic Unit (ALU)
The arithmetic-logic unit contains the electronic circuitry that
executes all arithmetic and logical operations. The arithmetic-logic
unit can perform four kinds of arithmetic operations, or mathematical
calculations: addition, subtraction, multiplication, and division. As
its name implies, the arithmetic-logic unit also performs logical
operations. A logical operation is usually a comparison. This particular
unit can compare numbers, letters or special characters. The computer
can then take action based on the result of the comparison.
Functions of a CPU |
This is a very important capability. It is by comparing that a
computer is able to, for instance, check the balance in your bank
account, whether there are unfilled seats on airplanes, whether
charge-card customers have exceeded their credit limits and whether one
candidate of a political party has more votes than another. Logical
operations can test for three conditions:
* Equal-to condition. In a test for this condition, the
arithmetic-logic unit compares two values to determine if they are
equal. For example: If the number of tickets sold equals the number of
seats in the auditorium, in which case the concert is declared sold out.
* Less-than condition. To test for this condition, the computer
compares values to determine if one is less than another. For example:
If the credit limit of your credit card is below LKR 250,000 then you
will not have ‘Super Customer Benefits’.
* Greater-than condition. In this type the computer determines if one
value is greater than another. For example: If the hours a person worked
a week are greater than 40, every extra hour is multiply by 1.5 times to
compute the usual hourly wage for overtime.
A computer can simultaneously test for more than one condition. In
fact, a logic unit can usually discern six logical relationships: equal
to, less than, greater than, less than or equal to, greater than or
equal to, and not equal.
Symbols that let you define the type of comparison you want the
computer to perform are called relational operators. The most common
relational operators are the equal sign (=), the less-than symbol , and
the greater-than symbol
Registers: Temporary Storage Areas
Registers are temporary storage elements for instructions or data.
They consist of electronic circuitry which can be illustrated by basic
logic gates. They are not a part of memory; rather they are special
additional storage locations that offer the advantage of speed.
Registers work under the direction of the control unit to accept, hold
and transfer instructions or data and perform arithmetic or logical
comparisons at high speed. The control unit uses a data storage register
the way a store owner uses a cash register-as a temporary, convenient
place to store what is used in transactions.
Computers usually assign special roles to certain registers,
including these registers:
* An accumulator, which collects the result of computations.
* An address register, which keeps track of where a given instruction
or piece of data is stored in memory. Each storage location in memory is
identified by an address, just as each house on a street has an address.
* A storage register, which temporarily holds data taken from or
about to be sent to memory.
* A general-purpose register, which is used for several functions.
To be continued
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