A Computer has five functional independant units like Input Unit, Memory Unit, Arithmetic & Logic Unit, Output Unit, Control Unit.
Input Unit :-
Computers take coded information via input unit. The most famous input device is keyboard. Whenever we press any key it is automatically being translated to corresponding binary code & transmitted over a cable to memory or proccessor.
Memory Unit :-
It stores programs as well as data and there are two types- Primary and Secondary Memory
Primary Memory is quite fast which works at electronic speed. Programs should be stored in memory before getting executed. Random Access Memory are those memory in which location can be accessed in a shorter period of time after specifying the address. Primary memory is essential but expensive so we went for secondary memory which is quite cheaper. It is used when large amount of data & programs are needed to store, particularly the information that we dont access very frequently. Ex- Magnetic Disks, Tapes
Arithmetic & Logic Unit :-
All the arithmetic & Logical operations are performed by ALU and this operation are initiated once the operands are brought into the processor.
Output Unit :– It displays the processed result to outside world.
Basic Operational Concepts
- Instructions take a vital role for the proper working of the computer.
- An appropriate program consisting of a list of instructions is stored in the memory so that the tasks can be started.
- The memory brings the Individual instructions into the processor, which executes the specified operations.
- Data which is to be used as operands are moreover also stored in the memory.
Add LOCA, R0
- This instruction adds the operand at memory location LOCA to the operand which will be present in the Register R0.
- The above mentioned example can be written as follows:
Load LOCA, R1
Add R1, R0
- First instruction sends the contents of the memory location LOCA into processor Register R0, and meanwhile the second instruction adds the contents of Register R1 and R0 and places the output in the Register R1.
The memory and the processor are are swapped and are started by sending the address of the memory location to be accessed to the memory unit and issuing the appropriate control signals.
- The data is then transferred to or from the memory.
Analysing how processor and memory are connected :–
- Processors have various registers to perform various functions :-
- Program Counter :- It contains the memory address of next instruction to be fetched.
- Instruction Register:- It holds the instruction which is currently being executed.
- MDR :- It facilities communication with memory. It contains the data to be written into or read out of the addressed location.
- MAR :- It holds the address of the location that is to be accessed
- There are n general purpose registers that is R0 to Rn-1
- Performance means how quickly a program can be excecuted.
- In order to get the best performance it is required to design the compiler, machine instruction set & hardware in a coordinated manner.
Connection B / W Processor & Memory
Connection B/W Processor & Memory
- The above mentioned block diagram consists of the following components
6) General Purpose Registers
7) Control Unit
- The instruction that is currently being executed is held by the Instruction Register.
- IR output is available to the control circuits, which generates the timing signal that control the various processing elements involved in executing the instruction.
- The Memory address of the next instruction to be fetched and executed is contained by the Program Counter.
- It is a specialized register.
- It keeps the record of the programs that are executed.
- Role of these registers is to handle the data available in the instructions. They store the data temporarily.
- Two registers facilitate the communication with memory.
These registers are:
1) MAR (Memory Address Register)
2) MDR (Memory Data Register)
Memory Address Register:
- The address of the location to be accessed is held by MAR.
Memory Data Register:
- It contains the data to be written into or to be read out of the addressed location.
A PC is set to point to the first instruction of the program. The contents of the PC are transferred to the MAR and a Read control signal is sent to the memory. The addressed word is fetched from the location which is mentioned in the MAR and loaded into MDR. This post thus contains all the important basic operational concepts.
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