1. The computer system

Before you can install or manage an operating system, you need to know what it runs on and what it works with. In this page you will learn the vocabulary that the rest of the module uses: system, hardware, software, firmware and the different kinds of computers.

How to use this page

1. Read sections 1 to 4 (about 40 minutes).
2. Practise with the Computer System Explorer lab: the tabs System parts, Inside the box, Software types and Right computer for the job match sections 1 to 4.
3. Answer the questions at the end and do Activity 1, 2 and 3.

1. What is a computer system?

A system is a set of interrelated parts that work together for a purpose. A bicycle is a system, and so is the human body. A computer system is a set of elements that work together to turn raw data into useful information.

A computer system has four basic elements:

Element	What it is	Examples
Hardware	The physical parts you can touch.	Processor, memory, disk, screen, keyboard, cables
Software	The programs and instructions that tell the hardware what to do.	Operating system, web browser, games, drivers
Data	The symbols the system stores and processes. They become information when they have context and meaning.	Photos, documents, a list of temperatures, a database
Users	The people who use, install, configure and maintain the system.	A student, a technician, an administrator

Many authors add a fifth element: procedures, the rules for using the system (backup policy, access rules, update schedule).

Think about a school library. The building, the shelves and the barcode reader are the hardware. The loan rules and the catalogue program are the software. The list of books and loans is the data. Students and librarians are the users. If one part fails (a broken reader, a bug in the program, wrong data, a user who does not know the rules), the whole service suffers.

1.1 What a computer system does

All computer systems perform five basic functions:

1. Input. They receive data or orders (keyboard, touchscreen, microphone, sensors, network).
2. Processing. The processor executes instructions to transform the data.
3. Storage. They keep data for later, in memory (short term) and on disks (long term).
4. Output. They show the results (screen, printer, speakers, network).
5. Control. Every step is a sequence of instructions that the processor fetches, decodes and executes, coordinated by the operating system.

Example: you take a photo with your phone and send it to a friend. The camera sensor captures the image (input). The phone processes it and compresses it (processing). The photo is saved in the storage (storage). The screen shows a preview (output) and the network sends it (output). The operating system coordinates all of this while you decide what to do (user).

2. Hardware and basic components

Hardware is every physical part of the computer system. Inside a typical PC you find these components:

Component	What it does	Notes
Case (chassis)	Holds and protects the parts and directs the air flow.	Different sizes: tower, mini tower, small form factor
Motherboard	Connects all the other parts and lets them communicate.	It decides which processor, memory and cards you can install
CPU (processor)	Executes the instructions of the programs and controls the other parts.	Measured in cores and GHz
Heat sink and fan	Take the heat away from the CPU.	Without cooling the CPU slows down or switches off
RAM (main memory)	Stores the programs and data that are in use now.	Volatile: it loses its content without power
Storage (SSD or HDD)	Keeps the operating system, programs and files.	Non-volatile: it keeps data without power
Graphics card (GPU)	Creates the image that you see on the screen.	It can be integrated into the CPU or be a separate card
Power supply (PSU)	Converts the mains electricity into the low voltages that the parts need.	Measured in watts
Expansion cards	Add features: network, sound, TV, capture.	Many are already integrated into the motherboard

Two ideas appear all the time in this module:

• RAM versus storage. RAM is fast and temporary: it is the work table. Storage is slower and permanent: it is the archive. When you open a program, the operating system copies it from the storage into the RAM.
• SSD versus HDD. An SSD stores data in flash memory chips and has no moving parts. An HDD stores data on spinning magnetic platters. The SSD is faster and silent, and the HDD usually gives more capacity for less money.

2.1 Peripherals

Peripherals are the devices that you connect to the computer to communicate with it or to store information. We classify them by the direction of the data:

Type	Function	Examples
Input	Send data into the computer.	Keyboard, mouse, webcam, microphone, scanner
Output	Show or reproduce information.	Monitor, printer, speakers, headphones
Input and output	Do both.	Touchscreen, headset with microphone
Storage	Save data (inside or outside the case).	External disk, USB flash drive, memory card
Communication	Connect computers with each other or with other devices.	Network card, Wi-Fi adapter, Bluetooth adapter

Most peripherals need a small program called a driver. The driver explains to the operating system how to talk to that specific device.

3. Software

Software is the set of programs, libraries and instructions that tell the hardware what to do. Without software the hardware is useless, and without suitable hardware the software cannot run. Software is not data: data is what programs work with, software is what works on the data.

3.1 Types of software

Type	What it is	Examples
System software	Software that the computer needs to work. It hides the hardware details from the user.	Operating system, drivers, system utilities
Application software	Programs for a specific task that the user wants to do.	Office suite, browser, games, video editor
Programming software	Tools that help programmers to create programs.	Compiler, interpreter, code editor, debugger
Firmware	Low-level software stored in a non-volatile memory inside a device. It controls that device’s circuits.	UEFI (or BIOS) of a PC, the software of a router, a TV or a washing machine

Applications cannot run without system software: a spreadsheet needs an operating system to use the memory, the disk and the screen.

Firmware: software inside hardware

Firmware lives in a chip (usually flash memory) soldered to the device. It is the first software that runs when you switch on a PC: the UEFI firmware checks the hardware and then starts the operating system. Printers, mice, USB drives, cameras and smart TVs also have firmware. You can update it, but only rarely, for example to fix a bug or add a feature.

3.2 Programming languages: compiler or interpreter?

A processor only understands machine language: instructions made of ones and zeros that depend on the type of processor. Programmers prefer languages that are easier to read, so their programs must be translated.

• Low-level languages are close to the hardware. Machine language is the real language of the CPU. Assembly uses short names for each machine instruction (one assembly instruction is one machine instruction).
• High-level languages are closer to human language and do not depend on a specific processor. Examples are Python, Java, C and JavaScript.

A high-level program is translated into machine language in one of two ways:

	Compiler	Interpreter
How it works	Translates the whole program before it runs and creates an executable file.	Reads and executes the program one instruction at a time.
Errors	Syntax errors are found before the program starts.	The program runs until it reaches the error.
Speed	The executable file usually runs fast.	Usually slower, because it translates while running.
Typical examples	C, C++	Python, JavaScript (many languages mix both ideas)

The tab Software types of the lab has a small simulator that compiles and interprets the same program, so you can see the difference with an error.

4. Types of computers

We can classify computers by their use and by their features.

By use: a general-purpose computer can run many different programs (a PC). A specific-purpose computer is built to do one task or a few tasks (an industrial robot).

By features:

Type	Typical use	Key features
Supercomputer	Weather forecasts, scientific simulation, large AI training	Thousands or millions of processor cores working in parallel; very high cost and energy use. Performance is measured in FLOPS. Almost all of them run Linux.
Mainframe	Banks, insurance, government: huge numbers of transactions	Built for reliability and for moving a lot of data; far fewer processors than a supercomputer; very expensive.
Server	Websites, databases, file and print services, virtualisation	Serves other computers (clients) over a network; works 24/7; has redundancy (RAID disks, two power supplies); often mounted in a rack.
Personal computer (PC)	Study, office work, internet, media	General purpose and low cost. Desktops, laptops, tablets and 2-in-1 devices.
Workstation	CAD, 3D modelling, video editing, data science	A powerful PC: many cores, a lot of RAM (often ECC), fast SSD, professional graphics card.
Embedded system	Cars, appliances, medical devices, sensors, routers	A small computer inside a larger product that does a fixed task, often with firmware or a real-time OS. Limited resources.

4.1 Supercomputer or mainframe?

They sound similar, but they solve different problems:

• A supercomputer is optimised for very complex calculations (science, engineering, military research). It has many thousands of processors working in parallel, and it is hard to program.
• A mainframe is optimised for a huge volume of simple operations (payments, bookings) that must never stop. Its key values are reliability, security and continuous operation.

The categories are not rigid

Cloud computing, virtualisation and system-on-chip designs blur the borders. A “server” can be a virtual machine in a data centre, and your phone is a PC with a different shape. Use the categories to understand the requirements of each system, not as strict boxes.

Check what you have learned

1. A friend says: “I changed my Windows laptop for a MacBook.” What changed more, hardware or software? Explain.

   Answer

   Both changed, because a laptop is hardware and the operating system is software. The processor, memory, screen and case are different (hardware), and the operating system and most applications are different too (software).

2. Classify these devices as input, output, input and output, storage or communication: scanner, projector, touchscreen, USB flash drive, Wi-Fi adapter.

   Answer

   Scanner: input. Projector: output. Touchscreen: input and output. USB flash drive: storage. Wi-Fi adapter: communication.

3. What is the difference between RAM and an SSD? Give one similarity and two differences.

   Answer

   Similarity: both store data. Differences: RAM is volatile (it loses the data without power), the SSD is non-volatile; RAM is much faster but smaller and more expensive per gigabyte, and it only keeps what is in use now, while the SSD keeps the files for a long time.

4. Which type of software is the UEFI of a PC, and where is it stored?

   Answer

   It is firmware. It is stored in a non-volatile flash memory chip on the motherboard.

5. A hospital needs a computer for a CT scanner’s control unit, a bank needs one for millions of card payments, and a school needs one for its internal website. Which type of computer fits each case best?

   Answer

   The control unit of the CT scanner is an embedded system. The bank’s payment processing fits a mainframe. The school website fits a server.

Glossary

English	Castellano
computer system	sistema informático
hardware	hardware, componentes físicos
software	software, programas
firmware	firmware, programa residente en el dispositivo
data / information	datos / información
user	usuario
motherboard	placa base
processor (CPU)	procesador (CPU)
RAM (main memory)	memoria RAM (memoria principal)
volatile / non-volatile	volátil / no volátil
storage	almacenamiento
peripheral	periférico
driver	controlador
compiler / interpreter	compilador / intérprete
supercomputer	superordenador
mainframe	ordenador central, mainframe
server	servidor
workstation	estación de trabajo
embedded system	sistema empotrado

Credits

This page adapts the SOM course notes by Moisés Mas Rocamora, Daniel Álvarez Santamaría and Jana Taboada León, licensed under CC BY-NC-SA 4.0. This page is shared under the same licence.