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# Basic Computer Organisation and Design Computer Science Engineering (CSE) Notes | EduRev

## Computer Science Engineering (CSE) : Basic Computer Organisation and Design Computer Science Engineering (CSE) Notes | EduRev

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1
Basic Computer Organization & Design
Computer Organization Computer Architectures Lab
BASIC  COMPUTER  ORGANIZATION  AND  DESIGN
â€¢ Instruction Codes
â€¢ Computer Registers
â€¢ Computer Instructions
â€¢ Timing and Control
â€¢ Instruction Cycle
â€¢ Memory Reference Instructions
â€¢ Input-Output and Interrupt
â€¢ Complete Computer Description
â€¢ Design of Basic Computer
â€¢ Design of Accumulator Logic
Page 2

1
Basic Computer Organization & Design
Computer Organization Computer Architectures Lab
BASIC  COMPUTER  ORGANIZATION  AND  DESIGN
â€¢ Instruction Codes
â€¢ Computer Registers
â€¢ Computer Instructions
â€¢ Timing and Control
â€¢ Instruction Cycle
â€¢ Memory Reference Instructions
â€¢ Input-Output and Interrupt
â€¢ Complete Computer Description
â€¢ Design of Basic Computer
â€¢ Design of Accumulator Logic
2
Basic Computer Organization & Design
Computer Organization Computer Architectures Lab
INTRODUCTION
â€¢ Every different processor type has its own design (different
registers, buses, microoperations, machine instructions, etc)
â€¢ Modern processor is a very complex device
â€¢ It contains
â€“ Many registers
â€“ Multiple arithmetic units, for both integer and floating point calculations
â€“ The ability to pipeline several consecutive instructions to speed execution
â€“ Etc.
a simplified processor model
â€¢ This is similar to what real processors were like ~25 years ago
â€¢ M. Morris Mano introduces a simple processor model he calls
the Basic Computer
â€¢ We will use this to introduce processor organization and the
relationship of the RTL model to the higher level computer
processor
Page 3

1
Basic Computer Organization & Design
Computer Organization Computer Architectures Lab
BASIC  COMPUTER  ORGANIZATION  AND  DESIGN
â€¢ Instruction Codes
â€¢ Computer Registers
â€¢ Computer Instructions
â€¢ Timing and Control
â€¢ Instruction Cycle
â€¢ Memory Reference Instructions
â€¢ Input-Output and Interrupt
â€¢ Complete Computer Description
â€¢ Design of Basic Computer
â€¢ Design of Accumulator Logic
2
Basic Computer Organization & Design
Computer Organization Computer Architectures Lab
INTRODUCTION
â€¢ Every different processor type has its own design (different
registers, buses, microoperations, machine instructions, etc)
â€¢ Modern processor is a very complex device
â€¢ It contains
â€“ Many registers
â€“ Multiple arithmetic units, for both integer and floating point calculations
â€“ The ability to pipeline several consecutive instructions to speed execution
â€“ Etc.
a simplified processor model
â€¢ This is similar to what real processors were like ~25 years ago
â€¢ M. Morris Mano introduces a simple processor model he calls
the Basic Computer
â€¢ We will use this to introduce processor organization and the
relationship of the RTL model to the higher level computer
processor
3
Basic Computer Organization & Design
Computer Organization Computer Architectures Lab
THE BASIC COMPUTER
â€¢ The Basic Computer has two components, a processor and
memory
â€¢ The memory has 4096 words in it
â€“ 4096 = 2
12
, so it takes 12 bits to select a word in memory
â€¢ Each word is 16 bits long
CPU RAM
0
4095
0 15
Page 4

1
Basic Computer Organization & Design
Computer Organization Computer Architectures Lab
BASIC  COMPUTER  ORGANIZATION  AND  DESIGN
â€¢ Instruction Codes
â€¢ Computer Registers
â€¢ Computer Instructions
â€¢ Timing and Control
â€¢ Instruction Cycle
â€¢ Memory Reference Instructions
â€¢ Input-Output and Interrupt
â€¢ Complete Computer Description
â€¢ Design of Basic Computer
â€¢ Design of Accumulator Logic
2
Basic Computer Organization & Design
Computer Organization Computer Architectures Lab
INTRODUCTION
â€¢ Every different processor type has its own design (different
registers, buses, microoperations, machine instructions, etc)
â€¢ Modern processor is a very complex device
â€¢ It contains
â€“ Many registers
â€“ Multiple arithmetic units, for both integer and floating point calculations
â€“ The ability to pipeline several consecutive instructions to speed execution
â€“ Etc.
a simplified processor model
â€¢ This is similar to what real processors were like ~25 years ago
â€¢ M. Morris Mano introduces a simple processor model he calls
the Basic Computer
â€¢ We will use this to introduce processor organization and the
relationship of the RTL model to the higher level computer
processor
3
Basic Computer Organization & Design
Computer Organization Computer Architectures Lab
THE BASIC COMPUTER
â€¢ The Basic Computer has two components, a processor and
memory
â€¢ The memory has 4096 words in it
â€“ 4096 = 2
12
, so it takes 12 bits to select a word in memory
â€¢ Each word is 16 bits long
CPU RAM
0
4095
0 15
4
Basic Computer Organization & Design
Computer Organization Computer Architectures Lab
INSTRUCTIONS
Instruction codes
â€¢ Program
â€“ A sequence of (machine) instructions
â€¢ (Machine) Instruction
â€“ A group of bits that tell the computer to perform a specific operation
(a sequence of micro-operation)
â€¢ The instructions of a program, along with any needed data
are stored in memory
â€¢ The CPU reads the next instruction from memory
â€¢ It is placed in an Instruction Register (IR)
â€¢ Control circuitry in control unit then translates the
instruction into the sequence of microoperations
necessary to implement it
Page 5

1
Basic Computer Organization & Design
Computer Organization Computer Architectures Lab
BASIC  COMPUTER  ORGANIZATION  AND  DESIGN
â€¢ Instruction Codes
â€¢ Computer Registers
â€¢ Computer Instructions
â€¢ Timing and Control
â€¢ Instruction Cycle
â€¢ Memory Reference Instructions
â€¢ Input-Output and Interrupt
â€¢ Complete Computer Description
â€¢ Design of Basic Computer
â€¢ Design of Accumulator Logic
2
Basic Computer Organization & Design
Computer Organization Computer Architectures Lab
INTRODUCTION
â€¢ Every different processor type has its own design (different
registers, buses, microoperations, machine instructions, etc)
â€¢ Modern processor is a very complex device
â€¢ It contains
â€“ Many registers
â€“ Multiple arithmetic units, for both integer and floating point calculations
â€“ The ability to pipeline several consecutive instructions to speed execution
â€“ Etc.
a simplified processor model
â€¢ This is similar to what real processors were like ~25 years ago
â€¢ M. Morris Mano introduces a simple processor model he calls
the Basic Computer
â€¢ We will use this to introduce processor organization and the
relationship of the RTL model to the higher level computer
processor
3
Basic Computer Organization & Design
Computer Organization Computer Architectures Lab
THE BASIC COMPUTER
â€¢ The Basic Computer has two components, a processor and
memory
â€¢ The memory has 4096 words in it
â€“ 4096 = 2
12
, so it takes 12 bits to select a word in memory
â€¢ Each word is 16 bits long
CPU RAM
0
4095
0 15
4
Basic Computer Organization & Design
Computer Organization Computer Architectures Lab
INSTRUCTIONS
Instruction codes
â€¢ Program
â€“ A sequence of (machine) instructions
â€¢ (Machine) Instruction
â€“ A group of bits that tell the computer to perform a specific operation
(a sequence of micro-operation)
â€¢ The instructions of a program, along with any needed data
are stored in memory
â€¢ The CPU reads the next instruction from memory
â€¢ It is placed in an Instruction Register (IR)
â€¢ Control circuitry in control unit then translates the
instruction into the sequence of microoperations
necessary to implement it
5
Basic Computer Organization & Design
Computer Organization Computer Architectures Lab
INSTRUCTION FORMAT
Instruction codes
â€¢ A computer instruction is often divided into two parts
â€“ An opcode (Operation Code) that specifies the operation for that
instruction
â€“ An address that specifies the registers and/or locations in memory to
use for that operation
â€¢ In the Basic Computer, since the memory contains 4096 (=
2
12
) words, we needs 12 bit to specify which memory
â€¢ In the Basic Computer, bit 15 of the instruction specifies
â€¢ Since the memory words, and hence the instructions, are
16 bits long, that leaves 3 bits for the instructionâ€™s opcode
Opcode
Instruction Format
15 14 12 0
I
11
mode
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