1. Computer Studies/ICT SS2
2014/2015 Session

2. THE CENTRAL PROCESSING UNIT
A central processing unit (CPU) is the hardware within a computer that carries out
the instructions of a computer program by performing the basic arithmetical, logical,
and input/output operations of the system.
An Intel 80486DX2, as seen from below
An Intel 80486DX2, as seen from above.
Two typical components of a CPU are the Arithmetic and Logic Unit (ALU), which
Performs arithmetic and logical operations like addition, subtraction, division and
multiplication. While the Control Unit (CU), extracts instructions from memory and
decodes them, and transmits the instruction to each unit.

3. COMPUTER DATA CONVERSION
Registers
Register is a temporary storage area for instructions or data. They are
not a part of memory; rather they are special additional storage
locations that offer the advantage of speed. It works under the
direction of the control unit to accept, hold, and transfer instructions
or data and perform arithmetic or logical comparisons at high speed.
Most operations are done on the register; the processor can’t directly
perform arithmetic in memory. For example, if you want to add 1 to a
memory address, the processor will normally do this by loading the
Initial value from memory into a register, adding 1 to the register, and
then saving the value back to memory. The width (in bits) of the
processor’s register determines how much data it can compute with
at a time. This is sometimes used to label the processor’s size.

4. Some types of registers are as follows:
MAR stand for Memory Address Register
This register holds the memory addresses of data and instructions. This register is used to
access data and instructions from memory during the execution phase of an instruction.
Suppose CPU wants to store some data in the memory or to read the data from the
memory. It places the address of the-required memory location in the MAR.
Accumulator Register
 This Register is used for storing the results that are produced by the System. When the
CPU generate results after processing data then all the results will be Stored into the AC
Register.
MDR meaning Memory Data Register, is the register of a computer’s control unit that
contains the data to be stored in the computer storage (e.g. RAM), or the data after a fetch
from the computer storage. It acts like a buffer and holds anything that is copied from the
memory ready for the processor to use it. MDR hold the information before it goes to the
decoder.
Index Register
 A hardware element which holds a number that can be added to (or, in some cases,
subtracted from) the address portion of a computer instruction to form an effective address.
Also known as base register. An index register in a computer's CPU is a processor register
used for modifying operand addresses during the run of a program.

5. MBR stand for Memory Buffer Register
MBR stand for Memory Buffer Register. This register holds the contents of data or instruction read from, or written in memory. It means that this register is used to store data/instruction coming from the memory or going to the memory.
Data Register
 A register used in microcomputers to temporarily store data being transmitted to or from a peripheral device.
Assignment
List three (3) differences between register and memory. Submit same when you resume