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A short class with Sarah and her students. The other ways are under More.
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Today, we'll start with how a computer executes a program. Can anyone tell me what happens when a program runs on a computer?
It reads the code and runs it, right?
Exactly! It follows a process. This process is called the instruction cycle. Do you remember the two main phases of the instruction cycle?
Fetch and execute?
Correct! Remember, 'Fetch' is grabbing the instruction from memory, and 'Execute' performs the instruction. An easy way to remember this is F.E., like the first letters of Fetch and Execute.
Now, let's dive into instruction formats. Each instruction typically contains an opcode and an operand. What do you think is the role of the opcode?
Doesn’t it specify what operation to perform?
Yes! The opcode tells the CPU what to do, while the operand might point to data in memory. An easy mnemonic here is 'O is for Operation', which can help you recall that the opcode describes what operation is needed.
In our discussion of program execution, we must talk about CPU registers like the Program Counter (PC) and the Instruction Register (IR). Can anyone explain the purpose of the Program Counter?
It keeps track of the next instruction to be fetched, right?
Spot on! The PC ensures the CPU knows where to go next. A good way to remember this is 'Program Counter = Next Step Locator'.
Next, let’s discuss how accumulator-based processors work. What do you know about the accumulator?
It stores intermediate results, right?
Absolutely! It’s like a ‘temporary storage’ for results of operations. You can remember this with the phrase, 'Accumulating results'.
The process of fetching and executing instructions in the CPU.
The code that specifies which operation to perform.
The reference or direct data associated with the opcode for execution.
A special register used to store intermediate results during calculations.
Indicates the memory address of the next instruction to execute.
Holds the instruction currently in execution.
Fetch to start, Execute the part; PC's the compass, IR is smart.
Imagine a factory where raw materials (fetch) come in, then workers (execute) create products. The assembly line (PC) tells the next step, while the basket (IR) holds what’s being worked on.
F.E. = Fetch and Execute to remember the phases.
P.I.R. = Program Counter, Instruction Register, Accumulator.
Term
What are the two phases of the instruction cycle?
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Term
What does an Opcode specify?
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Term
What is the role of the Program Counter?
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Term
What is the function of the Accumulator?
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Term
Describe the Instruction Register.
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The standard process in computing where an instruction is fetched and executed.
The part of an instruction that specifies the operation to be performed.
The part of an instruction that specifies the data or address upon which the operation is to be performed.
A register within the CPU that stores intermediate results of computations.
A CPU register that keeps track of the address of the next instruction to be fetched.
A register that holds the currently executing instruction.
This section explores the execution of computer programs and the structure of programming languages, focusing on instruction formats and the processor's functioning.
The section details how programs are executed by processors, elucidating the instruction cycle of fetch and execute phases. It describes different instruction formats, memory operations, the role of CPU registers, and programming languages' hierarchy.
This section delves into the fundamentals of program execution within computer architecture, detailing how a processor executes a program through a systematic approach involving multiple phases. The instruction cycle is critical to this process, comprising two main phases: Fetch and Execute. The Fetch phase involves retrieving the instruction from main memory, while the Execute phase carries out the instruction's defined operation.
The section further explains the format of instructions, emphasizing the significance of operand references and opcode structures for effective programming. Key concepts like the CPU's accumulator-based architecture are introduced, along with an overview of CPU registers such as the Program Counter (PC) and Instruction Register (IR). Additionally, it touches on the various levels of programming languages, providing insight into the abstraction levels from machine code to high-level languages.