How Computers Execute Programs
The CPU is the Central Processing Unit.
Which Part Does the Computing
When you run a program, such as a word processor, a game, or a small script, something inside the computer has to carry out its instructions. A computer is built from many different components, and each one has its own role. This article focuses on the component that has the central job of doing the actual computing, and on how it relates to the programs it runs.
What do you think happens?
Which component of a computer has the central job of doing the actual computing?
Reveal answer
The CPU (Central Processing Unit)
The source identifies one component as having the central job of doing the actual computing: the Central Processing Unit, usually called the CPU. The program is what gets executed; the CPU is the component that does the executing.
Defining the CPU
The CPU is the Central Processing Unit. It is the component of a computer that does the actual computing, and it is the component that executes programs.
The name itself points to its role. It is a unit that is central to the computer's processing work. Because of this central role, the CPU is often described as the brain or heart of the computer. Both descriptions are metaphors: they express that the CPU is the part the rest of the computer's work depends on for computing, not that it literally thinks or pumps blood.
The CPU is one component within a computer made of many components. Its defining responsibility is to do the actual computing, and its job is to execute programs.
The CPU Within the Whole Computer
A computer may contain many components, and the CPU is only one of them. The source does not list every other component, and this article does not need to. What matters for understanding program execution is the relationship: the computer is assembled from many parts, and one of those parts is the one identified as responsible for the actual computing.
Because the CPU is one component among many, it helps to keep two questions separate. The first is what a component is: a physical part of the computer. The second is what the component does: here, it does the actual computing and executes programs. Hardware and software answer these two questions differently, as the next section shows.
Program Versus Processor
A common source of confusion is treating the CPU and the program as the same kind of thing. They are not. The CPU is a component of the computer that does the computing. A program is what the CPU executes. The CPU is the one doing the work; the program is the set of instructions being worked through.
The edge in the comparison is one CPU executing programs, which is the relationship the source describes. The CPU is the component; the program is what it runs. Removing the program leaves the CPU in place, and the same CPU can be given different programs to execute. The program is not the component doing the computing.
Tracing One Program's Execution
Following a program through the CPU's role
A user starts a program on a computer. Using only the facts in the source, identify what is being executed, what component executes it, and what that component's central job is.
- 1Identify the program
The thing started by the user is a program, a set of instructions. It is what gets executed, not the component that executes it.
- 2Identify the executing component
The component that executes programs is the CPU, the Central Processing Unit. It is one component within the computer's many components.
- 3State the CPU's central job
The CPU's defining responsibility is to do the actual computing, and its job is to execute programs. This is why it is described as the brain or heart of the computer.
- 4Note what the source leaves out
The source states what the CPU does but does not describe the individual internal steps used to execute one particular instruction. Any claim about those steps would go beyond this material.
The program is executed by the CPU, which does the actual computing. The program and the CPU are distinct: one is the set of instructions, the other is the component doing the work.
Where the Source Stops
Mistakes About the CPU
Common mistake Treating the CPU and the program as the same thing
What it looks likeSaying 'my CPU is the word processor' when the word processor is a program.
Why it failsThe CPU is a computer component that does the computing. A program is the set of instructions the CPU executes.
Do this insteadSay 'the CPU executes the word processor program.' The CPU is the doer; the program is what gets done.
Common mistake Thinking the CPU is the only component of a computer
What it looks likeAssuming that because the CPU is central, nothing else in the computer matters.
Why it failsThe source states that a computer is made from many different components. The CPU is one of them, identified as the one with the central computing role.
Do this insteadDescribe the CPU as one component within a computer made of many components.
Common mistake Calling the CPU the brain or heart as a literal description
What it looks likeConcluding the CPU literally thinks or pumps blood.
Why it failsBrain and heart are descriptive comparisons. They express how central the CPU is to the computer's work.
Do this insteadUse the metaphor to mean central importance, and keep the precise definition: the component that does the actual computing.
Check Your Understanding
A friend says: 'The CPU is the program that runs when I open my browser.' Explain what is wrong with this statement, using the difference between a component and a program. Then state in one sentence what the CPU's role is when the browser runs.
Hints
- Ask whether the CPU is a physical component or a set of instructions.
- Look for which item the source describes as doing the actual computing.
- The browser is what gets executed; the CPU executes it.
Key Ideas to Remember
- 1The CPU is the Central Processing Unit, the component that does the actual computing.
- 2The CPU is one component within a computer made of many components.
- 3The CPU executes programs; the program is the set of instructions being executed.
- 4The CPU is a computer component, distinct from the programs it runs.
- 5The source does not describe the internal steps the CPU uses for each instruction.
Key Takeaways
- The CPU (Central Processing Unit) is the component of a computer that does the actual computing.
- The CPU is one component among the many that make up a computer.
- The CPU executes programs, and it is often described as the brain or heart of the computer.
- The CPU is a hardware component; a program is the set of instructions it executes.
- This material does not cover the internal steps the CPU uses to execute each instruction.