I spent my entire afternoon studying instructions in the computer system. I discovered a lot of amazing pieces of knowledge regarding instructions that I am about to share here. So, let's get started!!
What is Instruction?
In computer systems, an instruction is a set of machine language codes that tells the processor what operation to perform. Instructions can range from simple operations, such as adding two numbers together, to complex operations like loading and storing data from memory or performing complex mathematical calculations.
Each instruction is made up of two parts: an opcode and an operand. The opcode specifies the operation to be performed, while the operand specifies the data that the operation should be performed on.
Instructions are stored in memory as a sequence of binary digits (bits), and the processor fetches and executes them in sequence. A program consists of a sequence of instructions that the processor executes in order to perform a specific task or set of tasks.
The instruction set architecture (ISA) of a computer specifies the set of instructions that the processor can execute. Different processors can have different ISAs, which can impact the performance and capabilities of the system.
What is Opcode?
In computer systems, opcode stands for "operation code". It is a part of the instruction in machine language that specifies the operation to be performed by the processor.
The opcode is a binary code that represents a specific operation that the processor can perform, such as addition, subtraction, multiplication, or division. It tells the processor what type of operation to perform and what data to use.
For example, in the instruction "ADD 5,6", the opcode would be "ADD", which tells the processor to add the two operands "5" and "6" together. In another instruction "MOV AX,BX", the opcode would be "MOV", which tells the processor to move the value stored in register BX to register AX.
Each opcode has a unique binary code that the processor recognizes and executes. The set of opcodes that a processor can recognize is known as the instruction set architecture (ISA). Different processors may have different ISAs, which can impact their performance and capabilities.
What are types of instruction based on functionality?
In computer systems, instructions can be classified into several types based on their functionality and the way they operate on data. Here are some common types of instructions:
Arithmetic instructions: These instructions are used to perform basic arithmetic operations, such as addition, subtraction, multiplication, and division.
Logic instructions: These instructions perform logical operations such as AND, OR, and NOT on data. They are often used in conjunction with conditional instructions to make decisions based on the logical state of the data.
Data transfer instructions: These instructions are used to move data between memory and registers or between different memory locations.
Control transfer instructions: These instructions control the flow of program execution by changing the sequence of instructions. Examples include jump instructions and branch instructions.
Input/output instructions: These instructions are used to communicate with input/output (I/O) devices, such as keyboards, displays, and storage devices.
System instructions: These instructions perform system-level operations, such as interrupt handling and system calls.
These are just a few examples of the types of instructions that can be used in computer systems. The specific instructions available depend on the processor's instruction set architecture (ISA).
What are instructions types based on how many fields instruction has?
Instructions in computer systems can also be classified based on the fields they contain. Here are some common types of instructions based on the fields they have:
One-address instructions: These instructions have one operand field, which specifies the memory address where the operand is located. For example, "LOAD 100" loads the value stored in memory location 100 into a register.
Two-address instructions: These instructions have two operand fields, one for the source and one for the destination. For example, "ADD R1, R2" adds the value stored in register R2 to the value stored in register R1 and stores the result back in R1.
Three-address instructions: These instructions have three operand fields, which specify the source operands and the destination. For example, "MUL R1, R2, R3" multiplies the values stored in registers R2 and R3 and stores the result in R1.
Zero-address instructions: These instructions do not have any operand fields and operate on values stored in registers or on the top of a stack. For example, "POP" removes the top value from the stack and stores it in a register.
Immediate instructions: These instructions have an operand field that contains a constant value rather than a memory address or register. For example, "ADD R1, #10" adds the value 10 to the value stored in register R1.
These are just a few examples of the types of instructions that can be classified based on their fields. The specific types of instructions available depend on the processor's instruction set architecture (ISA).
How to find out the number of opcode bits in instruction?
To find out the number of opcode bits in an instruction, you need to know the instruction set architecture (ISA) of the processor.
In most ISAs, the opcode is located in the first few bits of the instruction. The number of opcode bits depends on the number of instructions supported by the processor. If the processor supports a small number of instructions, the opcode can be represented using fewer bits. If the processor supports a large number of instructions, the opcode will require more bits to represent.
For example, if a processor supports 16 instructions, the opcode can be represented using 4 bits (2^4 = 16). If the processor supports 256 instructions, the opcode will require 8 bits (2^8 = 256).
To determine the number of opcode bits in an instruction, you can consult the documentation for the processor's ISA. This will typically provide information on the format of instructions and the number of bits used for the opcode field.
How the program is broken down into instructions?
A program is broken down into instructions by a process called compilation or assembly.
Compilation is the process of translating a high-level programming language code (such as C++, Java, Python) into machine language code. The high-level language code is first converted into an intermediate code or assembly language code, which is then translated into machine language code by a compiler. The resulting machine language code consists of a sequence of binary instructions that the processor can execute.
Assembly, on the other hand, is the process of translating assembly language code (which is a low-level programming language) into machine language code. Assembly language code is typically easier to read and write than machine language code since it uses mnemonics to represent the machine language instructions. However, it still needs to be translated into machine language code before it can be executed.
During the compilation or assembly process, the high-level language code or assembly code is broken down into a series of instructions that the processor can execute. Each instruction typically consists of an opcode (which specifies the operation to be performed), one or more operand fields (which specify the data to be operated on), and any necessary addressing modes (which determine how the operands are accessed).
The resulting sequence of instructions is then loaded into memory and executed by the processor. Each instruction is fetched from memory, decoded, and then executed by the processor in a specific sequence determined by the program logic.
What does it mean when we say a computer is 8-bit in terms of instructions?
When we say that a computer is 8-bit in terms of instructions, we mean that its processor is designed to work with instructions that are 8 bits in length.
In computing, an instruction set architecture (ISA) defines the set of instructions that a processor can execute. Each instruction in an ISA consists of one or more fields, including the opcode, which specifies the operation to be performed, and the operands, which specify the data to be operated on.
In an 8-bit ISA, each instruction is 8 bits long, which limits the number of unique instructions that can be supported to 2^8 or 256. This means that the processor can only execute a limited set of instructions, which may limit its performance and functionality compared to processors with larger ISAs.
The first microprocessors developed in the 1970s were typically 8-bit processors. Examples include the Intel 8080, the Motorola 6800, and the Zilog Z80. While 8-bit processors are no longer widely used in modern computing devices, they still find applications in embedded systems, microcontrollers, and retrocomputing enthusiasts.