Computer Organization
The organization of the computer is defined by its internal registers, the timing and control structure and the set of instruction that it uses.The internal organization of a digital system is defined by the sequence of micro operations it performs on data stored in its registers.
The general purpose digital computer is capable of executing various micro operations and in addition can be instructed as to what specific sequence of operations it must perform. The user of a computer can control the process by mean of a program.
A program is a set of instructions that specify the operations,operands and the sequence by which processing has to occur.
A computer instruction is a binary code that specify a sequence of micro operations for computer.
Instruction code with data are stored in memory.The computer read each instruction from memory and place it in control register.
The general purpose digital computer is capable of executing various micro operations and in addition can be instructed as to what specific sequence of operations it must perform. The user of a computer can control the process by mean of a program.
A program is a set of instructions that specify the operations,operands and the sequence by which processing has to occur.
A computer instruction is a binary code that specify a sequence of micro operations for computer.
Instruction code with data are stored in memory.The computer read each instruction from memory and place it in control register.
Instruction Code
An instruction code is a group of bits that instruct the computer to perform a specific operation.
Operation Code (Opcode)
It is a part of instruction code.The operation code of an instruction is a group of bits that define such operation as add, subtract, multiply, shift and complement.
The number of bits required for the operation code of an instruction depends on the total number of operation available in computer.
The operation code must consist of at least n bits for a given 2ⁿ or less distinct operations.
For example: Suppose a computer has 64 distinct operations one of them being an ADD operation.The operation code consist of 6 bit. such as 2ⁿ->2⁶=64 where n=6
So with bit configuration 110010 (operand) assign to the ADD operation.
In this case computer issues a control signal to read the bits from memory and perform addition.
At this point we must recognize the relationship between a computer operation and micro operation.
The number of bits required for the operation code of an instruction depends on the total number of operation available in computer.
The operation code must consist of at least n bits for a given 2ⁿ or less distinct operations.
For example: Suppose a computer has 64 distinct operations one of them being an ADD operation.The operation code consist of 6 bit. such as 2ⁿ->2⁶=64 where n=6
So with bit configuration 110010 (operand) assign to the ADD operation.
In this case computer issues a control signal to read the bits from memory and perform addition.
At this point we must recognize the relationship between a computer operation and micro operation.
Instruction Code Format
Each computer has its own particular code format. Instruction code are specify by computer designer who design the architecture of computer.
Stored Program Organization
Organization of computer have one processor register and an instruction code format with two parts.
- The first part specifies the operation to be performed.
- Second specifies an address.
The memory address tells the control where to found operand in memory.
Above diagram show that instruction are stored in one section of memory and data in another section.Memory unit have 4096 word we need 12 bits to specify an address.
Here
2¹⁰ = 1024
2¹⁰ X 2² = 4096
2¹² = 4096
we have (2¹² X 2⁴) or 4096 X 16
So we have 16 bit memory word.
If we store each instruction code in one 16-bit memory word, we have available four bits for the opcode (operation code).
The control reads a 16-bit instruction from the portion of memory.It uses the 12-bit address of the instruction to read a 16-bit operand from the data portion of memory.
Here
2¹⁰ = 1024
2¹⁰ X 2² = 4096
2¹² = 4096
we have (2¹² X 2⁴) or 4096 X 16
So we have 16 bit memory word.
If we store each instruction code in one 16-bit memory word, we have available four bits for the opcode (operation code).
The control reads a 16-bit instruction from the portion of memory.It uses the 12-bit address of the instruction to read a 16-bit operand from the data portion of memory.
Accumulator (AC)
Computer have a single - processor register usually assign to it the name accumulator and label it (AC). The operation is performed with the memory operand and the content of AC.
If an operation is an instruction code does not need an operand from memory the rest of bit can be used for other purpose.
Example:Operations such as clear AC, complement AC and increment AC operate on data stored in the AC register. They do not an operand from memory.
If an operation is an instruction code does not need an operand from memory the rest of bit can be used for other purpose.
Example:Operations such as clear AC, complement AC and increment AC operate on data stored in the AC register. They do not an operand from memory.
- Introduction of Computer Organization
- Addressing Mode
- Common Bus System
- Control Unit
- Type of Instructions
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Content is Reference form Compute System Architecture, MORRIS M. MANO
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