Machine Organization
CHAPTER 3
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Lesson Outcomes
CPU /Microprocessor architecture
CPU processing methods
 Pipelining
 Superscalar
 RISC
 Multiprocessing
 Instruction Cycle
 Instruction Sets and Types


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CPU /Microprocessor
Architecture
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CPU/ Microprocessor Architecture
 What is the central processing unit (CPU)?
 It interprets and carries out the basic instructions
that operate a computer.

contained on a single integrated circuit called a
processor (micro) that is located on the motherboard.

contains two unit: Control Unit (CU) and Arithmetic
Logic Unit (ALU).
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CPU/ Microprocessor Architecture
• What is a microprocessor?
– also called the CPU
– A microprocessor or processor is the heart of the
computer or any computing device
– It is a semiconductor chip which can be
programmed to do various functions and performs
all the computational tasks, calculations and data
processing etc. inside the computer.
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CPU/ Microprocessor Architecture
– Today, there are several different manufactures of
computer processors. However, Intel and AMD are the
leaders in the PC market
– Example of microprocessor are Intel Core i7-3770K
Quad-Core Processor, AMD FX-8120 8-Core
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CPU Component
• The processor contains four key components:
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CPU/ Microprocessor
• The CPU deals with each instruction it is given in a series of
steps.
• Each step is repeated for each instruction. This series of
steps is called the machine cycle.
• machine cycle involves:
– fetching an instruction from main memory
– decoding the instruction (Translate the program instruction into the
commands that computer can process)
– executing the instruction (Carry out the commands one after
another )
– Store the result into main memory
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CPU/ Microprocessor
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Control Unit (CU)
• It works with the central processing unit (CPU) to instruct,
maintain and control the flow of information.
• CU is the “brain” of the microprocessor.
• It contains all that the microprocessor microprograms
• Microprogram is a set of microinstructions in a CPU, used
to implement machine instructions. They reside in an
internal ROM that cannot be accessed by the user. It
contains the entire instruction set which are permanently
embedded by the manufacturer).
• CU will controls and interprets the execution of instructions, by
following a sequence of actions that corresponds to fetch-execute
instruction cycle
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Control Unit (CU)
• To determine which instruction to be executed, CU
reads the contents of the program counter (PC)/
instruction pointer (IP).
• The instructions are then decoded by the Instruction
Decoder in the CU.
• Instructions are executed sequentially unless told
otherwise
• CU has a Memory Management Unit to supervise the
fetching of instructions and data from memory.
• The I/O interface is also part of the control unit.
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Control Unit (CU)
• Instruction Decoder
– Is properly part of the CU that decodes instructions that
are sent to the microprocessor.
– When an instruction is fetched from the memory, the
instruction is then sent to the instruction decoder to
be decoded or interpreted. Control signals will then be
issued to perform the necessary operation.
– The interpretation process is called instruction
decoding.
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Arithmetic Logic Unit (ALU)
• ALU is a digital circuit that performs many different
arithmetic and logical operation on input data. It performs
these operations as directed by the CU.
• All computation performed by the microprocessor is done
by the ALU
• In short ALU performs :
 arithmetic operations such as addition and
subtraction, division and multiplication
 all logic operations such as AND, OR, XOR etc
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Arithmetic Logic Unit (ALU)
Four Components/ Structure on ALU:
Comparator
Shifter
ALU
Logic
Register
Control
of ALU
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Component / Structure of ALU
Comparator
• Compares the magnitude of two numbers placed in buffer registers. The
comparator, used in conjunction with Status Register, will output the
results of the comparison.
• Performs such logic operations as AND, OR, XOR, etc.
Logic Register
• provides input path for control signals and facilitate the sequencing and
operation of each individual block of circuits.
Control of ALU
• move the contents of a register one or more positions left or right. Can also
perform a unique operation called rotate when used with status register.
Shifter
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Registers
• A single, permanent storage location within the
CPU used for particular defined purpose.
• Used to hold binary value (shorten using
Hexadecimal) temporarily for
– Storage,
– Manipulation, and/or
– Simple calculations.
• Register is the basic working components of the
CPU.
• Each register serves a particular purpose.
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Registers
• A register may hold:
data being processed
instruction being executed
memory or I/O address to accessed
keeps track of the status of the computer or conditions of calculations
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Registers
• Four primary operations by registers:
Register can be Loaded with values from other locations
(from other registers or memory location)
Data from other location can be Added or subtracted
Data can be Shifted or rotated right or left by one or more
bits. Important in implementing of multiplication and division
The value of data in register can be tested for certain
conditions (zeros, negative, etc).
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Registers
Control Unit contains several important register :• Instruction Register (IR)
– Holds the actual/current instruction being executed by
computer.
• Program Counter
– Both a counter and a register.
– The address in the program counter register is always
the address of the next instruction to be executed.
– The counter portion of the device generates sequential
address numbers.
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Registers
• Program Counter (cont)
– When the current instruction is finished, It then
increments, (adds 1 to the address)
– It then generate and puts the number (new address) in
the counter register (PC).
– the program counter generates an address and places it
on the address bus.
– When the current instruction is finished, the above steps
are repeated.
– Thus, the program counter continually generates
sequential address.
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Registers
• Memory Address Register (MAR)
– Holds the address of a memory location.
• Memory Data Register (MDR)
– Also known as Memory Buffer Register (MBR).
– Holds data/instruction value that is being stored to or
retrieved from the memory location currently addressed
by the memory address register.
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Registers
• Status Register (Flags)
– Allow computers to keep track of special
condition such as:
Arithmetic carry, sign and overflow
Power failure
Internal computer error
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Registers
• Status Register (Flags) - cont
– The Status register contains individual flags (1
bit for each flag)
– Status flags indicate the outcome of execution of
arithmetic and logical operations
– The control unit set (1) or reset (0) flags as a
result of conditions that arise during the
execution of instructions.
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System Clock
• The system clock is a device that produces periodic
sequence of pulses to control the timing of all
computer operations.
• These pulses define machine cycles.
• During each machine cycle, some activity occurs,
such as the execution of a micro-instruction.
• The interval between corresponding edges of two
consecutive pulses is called the clock cycle time.
• The pace of the clock or the clock speed is
measured by the number of cycles (ticks) per
second.
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System Clock
• Each tick is a clock cycle that determines when the
next step in the machine cycle will occur
– MHz – one million ticks per second of system clock
theoretically, capable of executing one million
instructions per second
– GHz – one billion ticks per second of system clock
• Therefore the faster the clock speed, the more
instructions the processor can execute per second.
• In some cases several instructions can be
executed in a single clock tick.
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• an instruction is fetched by the Control Unit during
instruction time (i-time) and executed by the ALU
during execution time (etime)
• together, both steps make up a single machine
cycle & the process is repeated until the program is
finished the clock drives
• the clock drives the process by generating pulses
at precisely timed intervals
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CPU PROCESSING METHODS
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CPU Processing Methods
• In this topic, you will be introduced to the
different and interrelated CPU processing
methods.
• The common goal is to increase the
performance of the CPU. Among the methods
are:
–
–
–
–
Pipelining
Superscalar
CISC and RISC
Multiprocessing
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CPU Processing Methods
• Performance – number of instructions executed in a
given amount of time.
• To increase computer performance, these techniques
are used:
– Separating the fetch unit / execute unit
• Allows independent, concurrent operation of the two units of the
fetch-execute cycle
– Overlapping between the fetch-execute cycles of sequences of
instructions (pipelining)
• This reduce the average time needed to complete an instruction.
– Executing more than one instruction in a clock cycle
(superscalar)
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CPU Processing Methods
• Separating the fetch unit/ execute unit
– Previously – instruction cycles are executed
one by one. A new instruction enters the
instruction cycle after the previous instruction
has completed execution.
– In the instruction cycle, two phases are
involved – fetch phase and execute phase.
– To increase performance, it is possible to
separate the two phase and perform them
concurrently.
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CPU Processing Methods
• Fetch unit - retrieves and decodes the
instructions
– Fetches the instructions in parallel
– Holds them in a buffer until it can be decoded
and executed.
– How many instructions in a buffer?
• Size of instruction
• Width of memory bus
• Size of buffer
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CPU Processing Methods
• Execute unit – performs actual instruction
execution
– Contains ALU and a portion of CU
– Identifies and controls the steps that comprise
the execution part of the instruction.
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CPU Processing Methods
(pipelining)
• Overlapping the instruction cycle of instructions.
– fetch the next instruction while executing the current instruction.
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Concept of Pipelining
• Laundry Example
• Ann, Brian, Cathy, Dave
each have one load of clothes
to wash, dry, and fold
• Washer takes 30 minutes
A
B
C
D
• Dryer takes 40 minutes
• “Folder” takes 20 minutes
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Without Pipeline Concept
6 PM
7
8
9
10
Midnight
11
Time
30
A
B
40
20 30
40
20 30
40
20 30
40
20
• Sequential laundry takes 6
hours for 4 loads
• If they learned pipelining,
how long would laundry
take?
C
D
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With Pipeline Concept
6 PM
T
a
s
k
O
r
d
e
r
7
8
9
10
11
Midnight
Time
30
A
B
C
40
40
40
40 20
• Pipelined laundry takes 3.5
hours for 4 loads
• Multiple tasks operating
simultaneously using
different resources
D
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CPU Processing Methods Superscalar
• Executing more than one instruction in
a clock cycle.
– Process more than one instruction per clock
cycle
– Instructions processed in parallel, with an
average rate of more than 1 instruction per
clock cycle through multiple execution units
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Superscalar Processing
• Process more than one instruction per
clock cycle
• Separate fetch and execute cycles as
much as possible
• Buffers for fetch and decode phases
• Parallel execution units
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Scalar vs. Superscalar Processing
With pipelining
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