Secondary Storage: Permanent Data

From Action to Result

When you interact with a computer, your action begins a cycle. You use an input device, the computer processes the resulting data, and an output device presents a result that you can perceive. This cycle is the input-process-output pipeline. Secondary storage becomes important when the processing needs data that was saved for later use, such as the contents of a file.

Input and Output Roles

An input device captures a user's action and sends data into the computer. A keyboard, mouse, touchscreen, microphone, or sensor can provide input. An output device receives data from the computer and presents it to the user. A screen, speaker, or printer can provide output. A network connection is also described as a possible destination for program output.

The physical devices do not normally pass raw physical actions directly to a program. Input controllers and output controllers translate between physical signals and digital information. This translation lets the CPU and the program work with data while the devices handle actions such as clicks, key presses, display, and sound.

Tracing a Saved File

Software Between Components

Software connects the hardware components into one interaction. A program tells the CPU what to do when input arrives and what data to send to output devices. The operating system and hardware drivers handle low-level communication with devices, so the programmer does not need to understand every electrical detail of a keyboard or monitor.

The Programmer as Coordinator

The programmer orchestrates the computer's resources rather than directly controlling the physical devices. The program specifies what the CPU should do with incoming data and what data should be sent to an output device. In a text editor, for example, the programmer provides the logic that reads a key press, updates the document, and tells the graphics card to redraw the screen.

A Key Press Through the System

Consider a text editor and the moment when you press the letter A on the keyboard. The keyboard detects the key press and sends the input into the computer. The input controller passes the information to the CPU. The text editor interprets the key press, updates the document, and sends instructions for the display to be redrawn. The monitor then presents the updated document to you.

This sequence can happen in milliseconds. The user experiences it as a responsive interaction because the result quickly returns through an output device. After perceiving the result, the user may perform another action, beginning the cycle again.

Mistakes to Avoid

• Treating input and output as the same role

  The keyboard captures the user's action and sends data into the computer. The screen presents data from the computer back to the user.

  Fix: Classify the device by the direction of the data it handles: into the computer is input; from the computer to the user is output.

• Thinking that storage is the final output

  Storage supplies the file data to the processing steps. In the source example, the graphics card and monitor present the file's contents.

  Fix: Separate retrieval from presentation. Storage provides data; an output device presents the result.

• Assuming that the programmer directly controls the physical device

  The source explains that programmers write instructions for the CPU, while the operating system and hardware drivers handle low-level device communication.

  Fix: Describe the programmer's role as coordinating resources through software.

• Describing the pipeline as one-way

  The user perceives the output and may respond with another input, creating a continuing interaction cycle.

  Fix: Trace the return to the user and recognize that a new user action can begin another cycle.

Practice the Data Path

What to Remember

1. Input devices capture user actions and send data into the computer.
2. The CPU and the running program process incoming data and decide what should happen next.
3. Storage supplies saved file data when processing needs to retrieve it for an interaction.
4. Output devices receive data from the computer and present the result to the user.
5. Programmers orchestrate input, processing, storage, and output through software; the operating system and hardware drivers handle low-level device communication.