IS 310 Chapter 4-1 (CPU Operation)

The ALU executes _____(a)____ instructions, in response to ...

Computation and comparison instructions in response to a signal from the control unit

During the fetch cycle, the control unit fetches

an instruction from primary storage

What are two things that the CPU does?

(1) Executes program instructions including computation, comparison, and branching (2) Directs all computer system actions including processing, storage, I/O, and data movement

What happens during the fetch cycle? (a) What about during the execution cycle? (b)

(a) Data inputs are prepared for transformation into data outputs (b) The transformation takes place and data output is stored in a register

What is CPU (the letters) What is the ALU? (The letters)

Central processing unit Arithmetic logic unit

What occurs when the CPU executes a program? (FROM BOOK)

A complex chain of events

What happens at the conclusion of the execution cycle?

A new fetch cycle is started

What is the instruction pointer?

Address of the next instruction to be read

During the execution cycle, the ALU Passes

Data inputs through internal circuits to perform the addition, subtraction, or other data transformation

During the fetch cycle, the control unit: fetches ... increments ... separates ... stores ...

Fetches an instruction from primary storage Increments the instruction pointer (address of the next instruction) Separates the instruction into two components (instruction code and data inputs to the instruction) Stores each component in a separate register

In the execution cycle, data inputs flow from ____ and the outputs flow to ...

From registers through processing circuitry and the outputs flows to one or more registers

During the fetch cycle, the control unit increments ____(a)____ and stores ....

Increments the instruction pointer and stores the instruction in the instruction register

During the execution cycle, the ALU: retrieves retrieves Passes Stores

Retrieves the instruction code from a register Retrieves data inputs from registers Passes data inputs through internal circuits to perform the addition, subtraction, or other data transformation Stores the result in a register

RECALL (From chapter 2) What are the three primary components of the CPU? [See figure 4.2]

The control unit, arithmetic logic unit (ALU), and a set of registers

The CPU constantly alternates between two stages:

The fetch cycle (instruction cycle) and execution cycle

During the fetch cycle, the control unit: What are the two components instructions get separated into?

The instruction code (or number) and the data inputs to the instruction

During the execution cycle, the ALU retrieves (2 things)

The instruction code from a register and data inputs from registers

When the first instruction has been executed, what happens next? The process continues until ...

The next instruction is read and executed The process continues until the programs final instruction has been executed

During the execution cycle, the ALU stores

The result in a register

When is the second program instruction retrieved, what about the third instruction? etc.

The second program instruction is retrieved during the second fetch cycle, the third instruction is retrieved during the third fetch cycle, etc.

*Fetch cycle* What does the control unit do if the instructions includes memory addresses of data inputs?

They are copied from memory and loaded into registers as inputs for the ALU

Whats the first step that happens when the CPU executes a program? (FROM BOOK PG 108) To start, ...

To start, the control unit reads the first instruction from primary storage

What does The Control Unit do?

directs flow of data to/from memory, registers, and the ALU

What does The ALU do?

executes computation and comparison instructions

The Registers are

storage locations within the CPU that hold ALU inputs, ALU outputs, and other data for fast access

The CPU is

the computer system's "brain"

Data movement instructions are executed by

the control unit itself

*CPU EXECUTING A PROGRAM* If the instruction is a computation or comparison instruction, How does the CPU handle this?

the control unit signals the ALU what function to perform, where the input data is located, and where to store the data output

*Fetch cycle* What does the control unit do if there are data inputs embedded in the instruction?

they are loaded into registers as inputs for the ALU