Functional Units of Computer

21CSS201T – Computer
Organization & Architecture

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 How information handled in computer
• Information's are categorized as Instructions and data
• Instruction
▪ Control transfer of information within a computer or between
computer and I/O devices
▪ Specify what arithmetic & logic operations to be performed
• Program – list of instructions to perform a task
• Data
▪ Numbers & encoded characters used by the instruction
▪ Operands
▪ Entire Program can be considered as data if it is processed by
another program.
▪ Example: compiler program converts high level language
source program into machine language called object
program.
• Instructions and data are stored in the memory
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How information handled in computer
•Each number, Character, Instructions are encoded as a string
of binary digits called bits. Example: string of 0’s and 1’s.
•Information handled by the computer should be encoded in
suitable format.
•BCD (Binary Coded Decimal) – each decimal digit is encoded
by 4bits.
•Alphanumeric characters also encoded in binary codes. Many
method available, the famous two methods are
• ASCII (American Standard Code for Information
Interchange) – each character is encoded by 7 bits.
• EBCDIC (extended binary-coded decimal interchange
code) - each character is encoded by 8 bits.

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Input unit
•Computer accept coded information through input
units
•Letter or Digit from input unit is automatically
converted into its corresponding binary code that
can be understood by the processor.
•Example: keyboard, mouse, joystick, touch pad etc
•Microphones
•Camera

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Memory Unit
• Store programs and data
• Two types – Primary and Secondary
• Primary
▪ Also called main memory (fastest memory)
▪ Made by Number of semiconductor storage
cells
▪ Each cell store one bit of information
▪ The cells are rarely read or write individually
instead the Storage cells are processed in group
of fixed size called words
▪ Memory organized in such a way that one word
is read/write in one basic operation
▪ Number of bits in each word is called word
length of computer. Example, 16,32,64 bits
▪ Program should be in primary memory at the
time of execution

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 Memory Unit
•Types of primary memory
RAM
▪A memory in which any location can be accessed in a short
and fixed amount of time after specifying its address is
called a random-access memory (RAM).
▪High speed storage medium accessed in minimum delay.
▪Memory access time: time required to access one word.
▪time is independent of the location of the word being
accessed
▪It typically ranges from a few nanoseconds (ns) to about 100
ns for current RAM units.
▪Volatile – does not hold data without power
▪Temporary storage
▪Read/write
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Memory Unit
•Types of primary memory

ROM
▪Non-Volatile –holds data without power
▪Example : computer bios

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Memory Unit
•CACHE Memoy
▪add-on to the main memory, a smaller, faster RAM
unit, called a cache
▪holds section of a program that are currently being
executed . Also holds associated data if any.
▪tightly coupled with the processor and is usually
contained on the same integrated-circuit chip.
▪The purpose of the cache is to help high instruction
execution rates.

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 Memory Unit
•Secondary Memory
▪primary memory is essential, but expensive and does not retain
information when power is turned off .
▪So additional, less expensive, permanent secondary storage is
used.
▪Used when large amount of data or programs have to be
stored.
▪or used when information is accessed infrequently.
▪Access times for secondary storage are longer than for primary
memory
▪Example : magnetic disk ,tapes, optical disk etc

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Arithmetic & Logic Unit
•Most of the computer operations are executed in
ALU of the processor
•Example: Suppose two numbers available in the
memory to be added means, that numbers are
brought into processor(ie. Registers available in
processor) and executed
•Sum may be stored in memory or retained in the
processor for immediate use.
•registers are high-speed storage elements.
•Each register can store one word of data.
•Access times to registers are even shorter than
access times to the cache unit on the processor chip.

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Output unit
•Counterpart of input unit
•Converts binary data format into a format that a
common man can understand
•Main functions is to deliver the processed result to
the world
•Example: monitor, printer etc
•Some units, such as graphic displays, provide both
an output function, showing text and graphics, and
an input function, through touchscreen capability.
The dual role of such units is the reason for using
the single name input/output (I/O) unit in many
cases.

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Control unit
•Operations of all the units discussed above are
coordinated by control unit.
•sends control signals to other units and senses their
states.
•Generates timing and control signals.
•Timing signals instruct when a given action should
takes place.
•Control signal instruct ALU what action is to take
place.

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Summary
•The operation of a computer can be summarized as
follows:
• The computer accepts information in the form of
programs and data through an input unit and stores it
in the memory.
• Information stored in the memory is fetched under
program control into an arithmetic and logic unit,
where it is processed.
• Processed information leaves the computer through
an output unit.
• All activities in the computer are directed by the
control unit.

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THANK YOU

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