Configuration of Computer - 1.2 - 1.5

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CONFIGURING A COMPUTER

CHAPTER-1

1.2   REVIEW OF THE BLOCK DIAGRAM OF A COMPUTER:

            A  Computer is designed using four basic units. They are:

1.       Input data

2.      Central processing  unit (CPU)

a.        Control unit

b.      Arithmetic and logic unit

3.      Memory  unit

4.      Out put unit

1.       Input unit: 

i)The Input unit basically links the external world or environment to the computer system. .

ii)The keyboard and mouse of a computer are the most commonly used input devices.

2.      Central processing unit (CPU):

i)To interpret the instructions in the program and execute them one by one.

The units are,.

a)      Control unit: Transfers the program instructions and data between various units.

b)      Arithmetic and logic unit (ALU): Arithmetic operations like (+, -,*,^,/), logical operations like(AND, OR, NOT) and relational operations like (<, >,<=,>=) are performed  in this  unit.

c)      Registers: To store the intermediate data.

3.      Memory unit: To store input , intermediate results and the output.

4.      Output data: To print or to display the results.

1.3 GENERAL STRUCTURE OF A CPU:

                       

i.        Program counter: To keep track of the memory address of next instruction which has to be executed.

ii.       Memory address register: i) specifies the address to memory where information can be found  ii)To point to a memory location where information is to be stored.

iii.      Memory data register / Memory buffer register: An interface between the central processing unit and memory.

iv.     Instruction register (IR): The instruction register holds the instruction until it can be decoded.

v.      Timing and control unit (TCU):i) The operations of the CPU should always be performed in a proper sequence.

ii)The timing and control unit is used to generate all internal and external control signals which carries the execution.

vi.    Instruction decoder (ID): i)An electronic hard ware which decodes the instruction .

ii)The instructions are further broken down into a set of micro operations so that they can be executed directly.

vii.  Arithmetic logic unit (ALU):  i)performs arithmetic, logical and relational operations.

ii)Results will be transferred back to the accumulator.

viii.     Accumulator (ACC): To store the initial, the intermediate and the final result of an instruction.

1.4 HOW INSTRUCITON IS EXECUTED?

            A basic instruction execution cycle can be broken down into the following steps:

1.       Instruction cycle

2.       Execution cycle

1.      Instruction cycle:

a.      Instruction Fetch

i)Program Counter holds the memory address of next instruction.

ii)Address transferred to Memory Address Register.

iii)Data transferred to Memory Data register based on CPU’s read request.

iv)Data transferred to Instruction Register.

v)Program Counter incremented to point out address of next data.

b.      Instruction decode:

i)Determines the type of instruction.

ii)Selecting signals accordingly.

2.      Execution cycle: i)Data will be processed by CPU and get stored in accumulator temporarily. ii)Then transferred to the main memory.

1.5 FACTORS AFFECTING THE PROCESSING SPEED

             

i.        Register size : i)Normally the register size in the processor will be of 32 bits.

ii)Smaller size  will reduce the speed.

ii.      Memory size: i)The  amount of RAM or main memory can also affect the speed.

ii)The size of the RAM may vary from 64 megabytes to 4 gigabytes.

iii.    Clock speed: i)The computers system clock sets the pace for the CPU by using a vibrating quartz crystal.

ii)Fast clock  can process more instructions.

. For example 1000MHZ processor performs 1000 million instructions per second.

iv.    Data bus capacity : i)The width of the data bus determines how many bits can be transmitted at a time between the CPU and other devices.

ii)width of the address bus give the amount of address space, which can be accessed at any instance of time.

v.       Cache memory  : i) A  high speed memory that contains the most recent data.

ii)  The cache memory  normally varies 512KB to 1MB.

iii)The more the cache the execution speed will be faster.

vi.    Instruction set: i)The set of basic commands the processor can understand and execute is called the instruction set.

ii)More the number of bits in a processor, the larger the instruction set.

For example, a 16- bit processor has larger instruction set than 8-bit processor.

vii.  Heat and heat dissipation: i)When the processor runs it generates heat and becomes too hot. ii)Installing an adequate cooling system is the solution