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

 Page 1


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


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