ما هي البرمجيات: تعليمات وبيانات وسلوك

Written Explanation

Hardware and software

A computer has two sides.

• Hardware is the physical equipment you could, in principle, touch: the CPU chip, the RAM, the SSD, the screen, the battery.
• Software is the set of instructions that tells the hardware what to do. You cannot touch it. It exists as stored data that the CPU reads and carries out.

An everyday comparison helps. A piano is hardware: strings, keys, wood. A piece of sheet music is something else: it does not make a sound on its own, but when a player follows it, the piano plays a specific tune. Change the sheet music and the same piano plays a different song. Software is the sheet music of the computer.

Remember from Module 1 that the CPU follows instructions one small step at a time. Those instructions have to come from somewhere. Software is where they come from.

The one-sentence definition

Software is a set of instructions, together with the data those instructions use, that tells a computer what to do.

Notice the two parts:

1. Instructions: what to do, step by step. "Add these two numbers." "If the password is wrong, show an error."
2. Data: the information the instructions read, change, or produce. A contact list, a photo, a bank balance, a game score.

Instructions: the recipe

Think about a recipe for pancakes. It says: take two eggs, mix with flour, heat the pan, pour a ladle, flip when bubbles appear. Every step is precise, because the cook will do exactly what is written and nothing more.

A computer is an extremely literal cook. It does not guess what you meant. If the recipe says "add the first number to the second", it does exactly that. That is why instructions for computers must be exact and complete.

Real software is made of a huge number of such steps, sometimes millions of lines of instructions, organized into groups so that people can understand them. You do not need to read any of it yet. You only need to know that a program is a list of instructions, and the CPU carries them out.

Data: the ingredients

Instructions work on data. In the pancake recipe, the eggs and flour are the data (the ingredients) and the recipe is the instructions.

In software, data can be:

• Typed by a user (a message you write).
• Read from storage (a saved photo).
• Received over the network (a weather forecast).
• Produced by the software itself (the total of your shopping basket).

You learned in Module 1 that all of it is stored as bits and bytes. That is true of instructions too: the instructions themselves are saved as data in files. This is a key idea: software is stored in the same kind of storage as your photos. The difference is not how it is kept; the difference is how it is used. The CPU treats instructions as things to do, and treats data as things to work on.

Behavior: what the software does

When instructions run on data, something happens: a photo gets brighter, a message gets sent, a map moves as you walk. We call what the software does, as you can observe it from outside, its behavior.

A useful way to think about behavior:

   input (data in)  ->  instructions run  ->  output (data out / action)

This is the same four-step picture from Module 1 (input, processing, storage, output), now seen from the software's side. Two things decide behavior: which instructions are there, and which data they are given. A calculator app with the data "2 and 3" outputs 5. The same app with "10 and 4" outputs 14. Same instructions, different data, different result.

The instructions also decide what kind of thing the device is. That brings us to the next idea.

Same hardware, many devices

A modern phone has a CPU, RAM, storage, a screen, a camera, a microphone, and a GPS receiver. That hardware does not change when you install an app. Yet the phone can be:

• A map, when a map app uses the GPS receiver and the screen.
• A camera, when a camera app uses the lens and stores photos.
• A game console, when a game app draws moving pictures and reads your touches.

Nothing physical changed. The software did. This is why computers are called general-purpose machines: the hardware can do many jobs, and the software chooses the job. Contrast this with a simple desk lamp, whose hardware does exactly one thing.

Where software comes from

People write software in a programming language, which is a way of writing instructions that is readable by humans, with strict rules. Java, which you will learn in this course, is one such language. The text a programmer writes is called source code.

The CPU cannot read source code directly. It understands only its own very basic instruction set, written in bits. So source code has to be converted into a form the computer can run. Different languages do this differently, and you will meet the details when you learn Java. For now, keep the simple chain:

  Programmer writes source code  ->  it is turned into runnable form  ->  CPU runs it

Once software has been prepared like this and stored on your device, running it means the operating system (Module 1) loads it into RAM and the CPU starts following the instructions.

Layers of software

Not all software is the same sort of thing. Roughly:

• The operating system manages the hardware and runs other software (Module 1).
• Applications are the programs you use for a purpose: a browser, a messaging app, a spreadsheet.
• Firmware is software stored inside a device, close to the hardware, that makes the device work. A washing machine controller is an example. We meet it properly in the next lesson.

All of them are software: instructions plus data. They differ in their job and in how close they sit to the hardware.

Is it software or is it data?

This question trips up beginners. A good test:

• If the thing is a list of steps that the computer runs, it is software.
• If the thing is information that software reads, shows, or changes, it is data.

A photo is data: you do not "run" a photo. The photo viewer is software: it runs and shows the photo. A text document is data, and the word processor is software. A song file is data, and the music player is software.

There is a grey area, which you should know about. Some files mix both. A web page, for example, is mostly data (text and pictures) but can also contain instructions that the browser runs (small programs written in a language called JavaScript). A spreadsheet can contain formulas. When in doubt, ask: does the computer carry this out as steps, or does it just read it? Parts of a single file can be both, and that is fine.