COMPUTER ORGANISATION

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COMPUTER ORGANISATION
Sri.S.A.Hariprasad Sr.Lecturer R.V.C.E Bangalore
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PERFORMANCE EQUATION
N S
T
R
N - Number of instruction (m/c) S Average steps
required to execute one machine instruction R-
Clock frequency
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PERFORMANCE IMPROVEMENT

• Cache memory
• Pipelining
• Superscalar execution

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CACHE MEMORY
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• Cache can be built within the processor L1
  cache
• Cache can be placed between main memory and CPU
  L2 Cache
• Cache size being small, currently required
  instructions and data for execution are stored in
  cache
• Entire instructions and data connected with
  program cannot be stored at a time, if program is
  big
• New set of programs (instructions and data) can
  be loaded by swapping the previous contents back
  into memory

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• Cache Hit If wanted item by CPU (instruction
  or data) is present in cache.
• Cache miss If wanted item by CPU is not present
  in cache
• To improve the performance hit ratio to be
  increased

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PIPELINING

• Normal sequence of execution in sequential
  machines will have the 4 phases fetching,
  decoding, executing, writing.
• Till the completion of instruction execution
  other instruction will not be fetched
• Only one unit will be active at a time

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• Pipelining Improves the throughput of the
  system
• Throughput No of instructions executed per
  second or per . unit time
• Perfecting Fetching of an instruction prior to
  it execution and placing them in instruction
  queue when some other instruction is under
  execution

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F
D
E
W
1st CLK CYCLE
F
D
E
W
2nd CLK CYCLE
F
D
E
W
3rd CLK CYCLE
F
D
E
W
4th CLK CYCLE
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PIPELINING CONCEPT OF EXECUTION
Eg ADD R1, R2, R3,(Assuming 4 clk cycle required
for execution) MOVE R4, R5 ( Assuming 4 clk cycle
required for execution)
T1
T2
T3
T4
T5
T6
T7
T8








ADD R1,R2,R3
MOVE R1,R2,R3
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F
D
E
W
ADD R1,R2,R3
F
D
E
E
MOV R4,R5
4
5
2
3
1
Clk cycles
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PERFORMANCE MEASURMENT

• SPEC Organization called system performance
  evaluation corporation
• Developed in the year 1995 and modified in the
  year 2000
• SPEC 95 uses SUN SPARC station 10/40 as standard
• SPEC 2000 uses ultra SPAC 10 with a 300 Mhz
  processor

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Running time on the reference computer
SPEC rating
Running time on the computer under test
SPEC rating
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MULTIPROCESSOR AND MULTICOMPUTERS
MULTIPROCESSOR SYSTEM System which uses more
than one processor unit. Advantage Different
application tasks can be executed in parallel
OR Single large task can be divided into small
task and are distributed to all processor
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• All the processor shares the memory
• Increased performance is achieved at the cost of
  increased complexity in design and debugging
• Different processor can communicate with each
  other using interconnection network
• Cost will also increase
• Increase software overhead for the design of
  optimized and sophisticated system software tool
  to integrate or coordinate different processor

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MULTICOMPUTER OR DISTRIBUTED SYSTEM

• Interconnected complete computer (own local
  memory) to achieve high computational power
• Information exchange is through communication
  network

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RISC CISC PROCESSOR

• CISC COMPLEX INSTRUCTION SET COMPUTER
• Complex instruction set
• Micro programmed control unit
• Frequent memory access
• Different length instruction formats
• More addressing modes

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• Instruction execution cycles are different
• Doesnt support HLL
• S.gt1, N small
• Less member of registers

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• RISC Reduced instruction set computers
• Reduced instruction set
• Hard wired control unit
• Memory access is limited to load and store
  operation
• Fixed instruction length
• Less addressing modes

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• Single cycle execution
• Support to HLL
• N gtgt1, S is small
• Supports pipelining

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DISADVANTAGES OF RISC

• RISC programs are longer than CISC program
• More memory is required to store more program
• Hence traffic between the memory and CPU will
  increase

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Computer Architecture It is an abstraction of a
physical computing system as seen by a machine
language programmer or a compiler
writer Computer Organization It refers to the
physical arrangement and interconnection of the
components in a computing system and the
characteristics of those components
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EXPECTED QUESTIONS

• Explain the various functional units of computer?
• Explain the steps involved in the execution of an
  instruction?
• Explain how performance of a system can be
  improved?
• Comment on
• (a) Performance (b) Performance execution (c)
  SPEC rating
• Explain the difference between RISC and CISC
  machines?
• Write a short note on computer software?
• Explain the difference between multiprocessor and
  multi computers?

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• Given the number of instruction in a program is
  10, average steps required is 4. Clock speed of
  processor is 4Mhz calculate the time taken to
  execute the program
• (b) If processor speed is increased to 8Mhz
  calculate the time required to execute the same
  program