knowverseWhat happens between fetching an instruction and executing it? Try 10 questions on the parts and operations of a simple processor.
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The ALU performs calculations and logic.
This component is the Arithmetic Logic Unit, or ALU for short. It is the part of the processor that does the actual 'thinking' and 'calculating'.
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The zero flag reports a zero-valued result.
The most common signal is the Zero Flag. It turns 'on' if the result of an operation is exactly zero.
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The opcode encodes an instruction's operation.
The specific part of an instruction that identifies the operation to be performed is called the Opcode.
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An instruction set specifies supported commands.
This complete collection of every possible command a specific CPU can execute is known as the Instruction Set.
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It coordinates transfers and operations.
The Control Unit acts as the central coordinator that manages every other part of the processor.
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The program counter tracks an instruction address.
The Program Counter is a high-speed storage location that holds the memory address of the next instruction to be executed.
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Fetching brings the next instruction into the processor.
Knowing the address is only the first part; the CPU must then actually get the data. This retrieval process is called Fetching.
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Decoding determines which operation the encoded instruction requests.
Decoding is the specific process where the Control Unit looks at the binary pattern to determine which action to take.
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A jump redirects instruction flow by changing the instruction address.
To break the straight-line flow, we use a Jump instruction, which manually overrides the Program Counter.
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Conditional branching chooses a path according to a result or condition.
This is called Conditional Branching. It allows the computer to take one path or another based on the result of a calculation.
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A processor contains parts with different roles. Registers hold values close to the working circuits. The arithmetic logic unit, or ALU, performs arithmetic and logical operations. The control unit coordinates transfers and selects the required operation. These roles explain how stored bits become the inputs and results of a computation.
An instruction tells the processor which action to perform. Its opcode identifies that action, while other parts may identify data or locations. The instruction set is the collection of commands a processor supports. In a stored-program design, instructions are represented as data that can be loaded into memory.
The specific part of an instruction that identifies the operation to be performed is called the Opcode.
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The program counter holds the address used to find the next instruction. Fetching retrieves an instruction from memory, and an instruction register holds it for processing. During decoding, the control unit interprets the instruction. Execution then activates the circuitry needed to carry out the requested operation on its inputs.
A program need not follow addresses in a simple straight sequence. A jump changes the next instruction address. A conditional branch selects a path based on a condition, such as an ALU result flag. In the model described here, a zero flag indicates that an operation produced zero, helping programs make decisions and repeat work.
The Program Counter is a high-speed storage location that holds the memory address of the next instruction to be executed.
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Sources: The Heart of the Machine. Each question or step includes an excerpt from the course.
