Transcript Central Processing Unit Part I

Central Processing Unit
Part I
Bayram Güzer
Central Processing Unit
• Central processing unit is a control center that
converts data input to information output.
– It includes complex set of electronic circuit
components.
– It executes stored program instructions
• Central processing unit consist of two main
parts;
– Control unit
– Arithmetic logic unit
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Central Processing Unit
• CPU interacts closely
with memory (primary
storage).
• Memory often
regarded in the context
of the central
processing unit
however it is not part
of the CPU, it is a
seperate piece of unit.
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Central Processing Unit
• Memory holds the
data temporarily at the
time the computer is
executing a program.
• Secondary storage
holds permanent or
semipermanent data
on some external
medium until it is
needed for processing.
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Control Unit
• The control unit contains circuit
components that uses electrical signals to
direct the entire computer system to execute
stored program instructions.
– Like the orchestra leader
– It doesn’t execute program instructions but it
directs other parts of the system to do so.
– It communicates with both arithmetic/logic unit
(ALU) and memory.
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Arithmetic/Logic Unit (ALU)
• The ALU contains the electronic circuit
components that executes all arithmetic and
logical operations.
• ALU performs four kinds of arithmetic
operations;
–
–
–
–
Addition
Subtraction
Multiplication
Division
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Arithmetic/Logic Unit (ALU)
• Logical operation is usually a comparison.
The unit can compare;
– Numbers
– Letters
– Special characters
• Logical operations can test three conditions
– Equal to, less than and greater than condition.
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Arithmetic/Logic Unit (ALU)
• Equal-to condition
– Compares two values to determine if they are equal
• Less-than condition
– Compares two values to determine if one is less
than another
• Greater-than condition
– Compares two values to determine if one is greater
than another.
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Arithmetic/Logic Unit (ALU)
• Combined conditions
– Less-than or equal to
• Checks to find if one value is less than or equal to the
other value.
– Greater-than or equal to
• Checks to find if one value is greater than or equal to the
other value
– Not equal to (literally sometimes referred as greater
than or less than)
• Checks to find if one value is not equal to the other value
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Arithmetic/Logic Unit (ALU)
• Relational operators are the symbols which
lets you define the type of comparison you
want the computer to perform
Explanation
C-like
BASIC-like
Equal to
==
=
Not equal to
!=
<>
Greater than
>
>
Less than
<
<
Greater than or equal to
>=
>=
Less than or equal to
<=
<=
C-like: C, C++, C#,
Java, Perl, PHP,
Javascript
Basic-like: Basic,
Pascal, SQL.
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Registers
• Registers are special-purpose, high-speed,
temporary storage areas for instructions of data.
– Not part of memory
– Special additional storage locations
– High-speed access is available
• Registers work under the direction of the control
unit
– To accept, hold, and transfer instructions or data
– To Keep track of where the next instruction to be
executed or needed data is stored
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Registers
• Some of the register types are;
– Address register: keep track of where a given
instruction or piece of data is stored in memory.
– Storage register: temporary holds data taken
from or about to be sent to memory.
– Accumulator: collects the results of
computations.
– There are other types of registers which is used
for several functions as well.
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Memory
• It is also known as primary storage and main memory
– Often expressed as random-access memory (RAM)
– Not part of the CPU
• Memory stores program instructions or data as long as it
is in the operation and has not been terminated.
• The CPU cannot process data from an input device or
disk directly, therefore the data must first be available in
memory.
• Control unit is responsible from;
– Receiving the items from memory
– Sending the items from memory
– Transferring the items from memory to secondary storage.
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Memory
• It is also known as primary storage and main
memory
– Often expressed as random-access memory (RAM)
– Not part of the CPU
• Memory stores program instructions or data as
long as it is in the operation and has not been
terminated.
• The CPU cannot process data from an input
device or disk directly, therefore the data must
first be available in memory.
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How the CPU Executes
Instructions
• Before an instruction
can be executed,
program instructions
and data must be
placed into memory
from an input device
or a secondary storage.
Control Unit
ALU
3
Execute
2
Decode
1
Fetch
I-Time
E-Time
4
Store
Memory
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How the CPU Executes
Instructions
• Instruction has been
executed in 4 different
steps;
–
–
–
–
Fetch
Decode
Execute
Store
Control Unit
ALU
3
Execute
2
Decode
1
Fetch
I-Time
E-Time
4
Store
Memory
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How the CPU Executes
Instructions
• Fetch: The control unit
gets the instruction from
the memory
• Decode: The control
unit decodes the
instruction and directs
the necessary data to be
moved from memory to
the ALU.
• The first two steps are
together are called as
instruction time (I-time)
Control Unit
ALU
3
Execute
2
Decode
1
Fetch
I-Time
E-Time
4
Store
Memory
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How the CPU Executes
Instructions
• Execute: The arithmetic
logic unit executes the
arithmetic or logical
instructions by performing
the actual operations on real
data.
• Store: The arithmetic logic
unit stores the result of this
operation in memory or in a
register.
• Step 3 and 4 together are
called as execution time (Etime).
• The combination of I-time
and E-time is called as
machine cycle.
Control Unit
ALU
3
Execute
2
Decode
1
Fetch
I-Time
E-Time
4
Store
Memory
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How the CPU Executes
Instructions
• Each central
processing unit has an
internal clock that
produces pulses at a
fixed rate to
synchronize all
computer operations.
• Pulses are electronic
signals like heart beat,
clock beat, or school
ring.
Control Unit
ALU
3
Execute
2
Decode
1
Fetch
I-Time
E-Time
4
Store
Memory
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How the CPU Executes
Instructions
• Clock pulse has two
stage;
– high voltage (like a
tick sound) - ON
– Low voltage (like a
tock sound) - OFF
• Clock tells circuits
when to start sending
data on wires and
when not to sent data
on wires.
Control Unit
ALU
3
Execute
2
Decode
1
Fetch
I-Time
E-Time
4
Store
Memory
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How the CPU Executes
Instructions
• Instruction set is a
specific group of
instructions which
each type of CPU is
designed to
understand.
Control Unit
ALU
3
Execute
2
Decode
1
Fetch
I-Time
E-Time
4
Store
Memory
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How the CPU Executes
Instructions
• SET TOTAL TO 0
• ADD NEXT
NUMBER TO
TOTAL DATA:88
• ADD NEXT
NUMBER TO
TOTAL DATA: 76
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How the CPU Executes
Instructions
• Fetch: fetch the instruction
from the memory
• Decode: control unit
determines that addition
must take place and gives
instructions for the next
number
• Execute: ALU does the
addition, increasing the
total to 164
• Store: ALU stores the new
total in the register and
removes old value in the
register.
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How Control Unit Finds
Instructions and Data
• Each memory location has
identified by an address
– A unique number, much like
a mailbox
• Each memory location may
contain only one instruction
or piece of data
– When data is written back to
memory, previous contents of
that address are destroyed
• Each address is referred to
by number but
– Programming languages use
a symbolic (named) address,
such as Hours or Salary
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References
• Capron, H. L. (2000). Computers Tools for an
Information Age.(6th ed.). New Jersey, USA:
Prentice Hall.
• http://homepage.cs.uri.edu/faculty/wolfe/book/Read
ings/Reading04.htm
• http://en.wikipedia.org/wiki/Pulse_%28signal_proce
ssing%29
• http://www.yale.edu/pclt/PCHW/clockidea.htm
• http://www.camiresearch.com/Data_Com_Basics/da
ta_com_tutorial.html
• http://en.wikipedia.org/w/index.php?title=Relational
_operator
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