Organisation & architecture of CPU

1. CPUCPU
ORGANISATIOORGANISATIO
NN

2. CPU (CPU (Central Processing UnitCentral Processing Unit))
Acts as the brain of computer.
Performs all the calculations & controls all the
components.
Carries out the instructions of a computer
program, performs the basic arithmetical,
logical, and input and output operations of the
system.

4. CPU Has Two MainCPU Has Two Main
ComponentsComponents
 Control Unit
(CU)
 Arithmetic &
Logic Unit (ALU)

5. Control UnitControl Unit
Selects program instructions & coordinates
their execution.
Regulates timing of processor.
Sends control signal to and receives control
signal from peripheral devices.
Acts as central nervous system for all other
components.
It obtains instruction from memory, interprets
the instruction & issues signals to the required
units to carry out the execution.

6. ALUALU
Actual execution of instruction takes place
in ALU.
It consists of a complicated set of logic
circuit, registers and accumulator to carry
out all operations.
Depends on the commands given by the
Control Unit.

7. RegistersRegisters
It holds data temporarily during the execution
of instruction.
They are a part of CPU.
Length of register = No. of bits in can store.
Two types -
 Special Purpose Registers
 General Purpose Registers

8. List of Special Purpose RegistersList of Special Purpose Registers
Decoder
Program Control Register
Memory Address Register
Memory Buffer Register
Instruction Register
I/O Register
Accumulator

9. Decoder
It interprets the instruction to be executed.
Program Control Register
• It holds the address of next instruction to be
executed.
• In case of branch instruction, system passes
the address part of branch instruction to PC.
Memory Address Register
It holds the address of the active memory
location.

10. Memory Buffer Register
 It holds the content of accessed memory
word.
 It holds the data word when it is transferred
to and from the main memory.
Instruction Register
 It holds the instruction being executed.
 Instruction is divided into two parts :
Operation Part - Given to MAR
Address part - Given to Decoder

11. I/O Register
 It is used for communication with the I/O devices.
 An input unit transfers all the contents to this register
& then system picks up the data & vice-versa.
Accumulator
 It holds the data under execution, intermediate results
& result of operations.
 Result  Accumulator MBR  Main Memory

12. Main MemoryMain Memory
 RAM (Random Access Memory)
 Volatile Memory
 Every file or application opened is placed in RAM
 Uses Random Access Technique, i.e., the data can be
directly jumped to the middle if necessary without having
to read the data sequentially.

14. ROM (Read Only Memory)ROM (Read Only Memory)
 Non-volatile Memory
 The instructions are stored by manufacturers
 Special programs are stored called micro-programs
which deal with low-level machine functions.
 Types of ROM --
PROM(Programmabl e ROM)
EPROM(Eras abl e Programmabl e
ROM)

15. Cache MemoryCache Memory
 Extremely fast & small memory
 Placed between CPU & Main memory
 Used for temporarily storing active data & for minimizing
the data fetch time
CPU
Cache
Memory Main
Memory

16. Steps of Execution Of InstructionSteps of Execution Of Instruction
1 ) The CUtake s addre ss o f the ne xt instructio n
fro m the PC Re g iste r & re ads the instructio n
fro m co rre spo nding m e m o ry addre ss into the
Instructio n Re g iste r.
2) CUthe n se nds the o pe ratio n & addre ss part
to De co de r & MAR re spe ctive ly.
3) De co de r inte rpre ts the instructio n se nds
co m m and sig nals to the appro priate units to
carry o ut the task spe cifie d.
4) As the syste m e xe cute s e ach instructio n, it
lo ads the addre ss o f ne xt instructio n in PC
Re g iste r & re pe ats ste ps 1 to 4.

17. Thank You
Thank You