What Is Software? The Invisible Part That Tells the Machine What to Do
If you can drop it on your foot, it is hardware. Everything else is software: the instructions that decide what the hardware actually does.
The whole idea, in one diagram
Hardware is the body. Software is the set of instructions the body follows.
The operating system is the boss that shares the screen, memory and storage between everything.
Apps sit on top, each one a program written for a particular job.
What problem did it solve?
Early computers were wired for one job. Changing what ENIAC did meant a team of people physically moving cables and flicking switches for days. The machine and the task were welded together.
Instructions were stored in the computer's memory as numbers, exactly like the data. Change the numbers and the machine does a different job, with no rewiring at all.
One machine can be a calculator, a drawing board, a cinema and a classroom before lunch. Every app, game and website you have ever used exists because of that one idea.
How it started
- 1936 to 1945
The stored program idea
👤 Alan Turing, then John von Neumann and colleagues
The insight that instructions could be kept in memory as numbers, alongside the data they work on, instead of being built into the wiring.
Why it mattered: This is the single idea that separates a computer from a machine. It is why one device can run millions of different programs.
- 1947
The most famous bug in history
👤 Grace Hopper's team at Harvard
A machine was misbehaving. The team opened it up and found a real moth stuck in a relay. They taped it into the logbook and wrote that they were debugging the machine.
Why it mattered: Engineers had called faults bugs before this, but that taped moth is why every child learning to code today talks about bugs and debugging.
- 1952
Computers learn to read human words
👤 Grace Hopper, USA
She built a compiler, a program that turns instructions written in something close to English into the numbers a machine can run. People told her computers could not understand English.
Why it mattered: Before this you wrote raw machine numbers. Afterwards, ordinary people could learn to program, which is why there are millions of programmers rather than a few hundred.
- 1969
Software takes people to the Moon
👤 Margaret Hamilton and her team at MIT
She led the flight software for Apollo. Minutes before landing, her code spotted that it was overloaded, threw away the least important jobs and kept the landing running.
Why it mattered: She also pushed for the phrase software engineering to be taken seriously, at a time when writing code was not treated as real engineering.
- 1970s to 1980s
The operating system becomes the boss
👤 Unix, then MS-DOS, Mac and Windows
Instead of every program controlling the whole machine, one program took charge of the screen, the memory, the files and the keyboard, and lent them out to the others.
Why it mattered: It is why you can have a browser, music and a game open at once without them fighting, and why one program crashing rarely takes the whole computer down.
- 1991
Software anyone can read and share
👤 Linus Torvalds, Finland
A student released the core of an operating system and let anybody read, change and share the instructions for free. Thousands of people improved it.
Why it mattered: Most of the internet's servers, and every Android phone, run on this. Free and open software is now a huge part of everything you use.
- 2008 onwards
Software becomes something you tap once
👤 App stores on phones
Buying software stopped meaning a shop, a box and a disc. It became a tap, a download and an automatic update.
Why it mattered: It also made software something that keeps changing after you get it, which is good for fixes and means the thing you own is never quite finished.
Who made it happen
Grace Hopper
1906 to 1992 · USA
Built the first compiler so people could write programs in words instead of numbers, and helped make the famous bug story famous.
Margaret Hamilton
born 1936 · USA
Led the Apollo flight software and helped establish software engineering as a serious discipline.
Alan Turing
1912 to 1954 · England
Showed that a single machine could run any set of instructions, which is the idea underneath all software.
Linus Torvalds
born 1969 · Finland
Released Linux in 1991 and let anyone read and improve it. It now runs most servers and every Android phone.
Dennis Ritchie
1941 to 2011 · USA
Created the C language and helped build Unix. An astonishing amount of today's software is descended from his work.
Ada Lovelace
1815 to 1852 · England
Wrote the first program in 1843, before any machine existed to run it. The first ever piece of software.
What happens when you tap an app icon
- 1
You tap the icon
The icon is not the program. It is a picture that points at a file in storage, in the same way a name on a door is not the room.
- 2
The operating system loads it
The OS finds the program file in storage and copies it into memory, because storage is far too slow for the processor to work from directly.
- 3
The instructions become numbers
What gets loaded is a long list of very simple numbered instructions: add these, compare those, jump back. A person wrote them in words, and a translator turned them into this.
- 4
The processor runs them, one by one
The CPU reads an instruction, does it, then reads the next, billions of times a second. The operating system keeps interrupting to give other programs a turn too.
- 5
The OS lends it a window
The app cannot touch the screen directly. It asks the operating system for a window, and the OS decides where it goes and what is on top. That is why apps do not scribble over each other.
- 6
Anything you want to keep goes back to storage
Memory is emptied when the power goes. Saving copies your work into storage, which is exactly why unsaved work disappears when a machine switches off suddenly.
Hardware is the body and software is the instructions. The same machine becomes a calculator, a cinema or a classroom depending only on which numbers are loaded into its memory.
Open the settings on a phone or laptop and find the list of installed apps and how much space each one uses. Every one of those is software sitting in storage doing nothing at all, until somebody taps it and the operating system loads it into memory.
Quiz: how much did you remember?
Quiz time!
10 questions, picked at random from 30. No sign-in and no score is kept. Play as many times as you like, the questions change every time.
Questions about software
What is software in simple words?
Software is a set of instructions that tells the hardware what to do. It is not a physical thing you can hold. It is more like the recipe than the kitchen.
What is the difference between hardware and software?
Hardware is anything you can touch: the screen, the keyboard, the chips, the battery. Software is the instructions those parts follow. A useful test is that if you can drop it on your foot, it is hardware.
What is an operating system?
The operating system is the program in charge. It shares the screen, memory, storage and keyboard between all the other programs. Windows, macOS, Android, iOS and Linux are operating systems.
Why is a mistake in a program called a bug?
Engineers had used the word for faults before, but the famous story is from 1947, when Grace Hopper's team found a real moth stuck inside a machine and taped it into the logbook. Fixing mistakes has been called debugging ever since.
What is a file?
A file is a named lump of information kept in storage: a photo, a song, a letter, a program. Folders are just a way of grouping files so that people can find them again.
Why do I lose my work when the power goes off?
Because you were working in memory, which is fast but empties when the electricity stops. Saving copies your work into storage, which keeps it. This is why saving often is such good advice.
Why do apps need updates?
Because software is never truly finished. Updates fix mistakes, close security holes that criminals could use, and sometimes add new features. Ignoring updates for a long time is genuinely risky.
Is a website software?
Yes. A website is made of files and instructions that a browser runs. The difference is that you do not install it, you fetch a fresh copy from a server every time you visit.
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