Mission 1 · Spec 1.5.1
The operating system
The five jobs of an operating system: user interface, memory management and multitasking, peripheral management and drivers, user management, and file management.
- Starter 5 min
- Learn 10 min
- Lab 20 min
- Quiz 10 min
- Exam 10 min
Who's in charge?
You're streaming music, downloading a game and writing an essay at the same time, while a printer prints. What decides who gets the CPU, the memory and the printer?
Reveal
The operating system. It manages the hardware and shares it fairly between the programs that are running.
Functions of an operating system
User interface
Lets the user interact with the computer, e.g. a graphical user interface (windows, icons, menus, pointer) or a command-line interface.
Memory management and multitasking
Allocates RAM to each program, moves data between RAM and virtual memory, and switches the CPU rapidly between programs so they appear to run at the same time.
Peripheral management and drivers
Communicates with input and output devices. A device driver is software that translates the OS's instructions into commands a particular device understands.
User management
Creates and manages user accounts, logins and access rights, so each user sees only their own files and settings.
File management
Organises files into folders, and lets users name, move, copy, delete and search for files. Controls who can read or edit each file.
Match the function
Memory management in action
Exam-style questions
1. Describe how an operating system manages peripherals.
[2 marks]Mark scheme
- Uses device drivers to communicate with peripherals (1)
- Drivers translate OS instructions into commands the device understands / manages data transfer to and from devices / handles errors (1)
2. Explain how the operating system allows multitasking.
[2 marks]Mark scheme
- Programs are loaded into different areas of memory (1)
- The OS switches the CPU between programs very quickly so they appear to run at the same time (1)
3. State two features of user management.
[2 marks]Mark scheme
- Any two: creating / deleting user accounts; login with username and password; setting access rights / permissions; separate user settings and files (1 each)
TUTOR NOTES
- Misconception: the OS is an application. It's system software.
- Exam habit: give an example for each function; it makes descriptions concrete.
Mission 2 · Spec 1.5.2
Utility software
Encryption, defragmentation and data compression software: what they do and why computers need them.
- Starter 5 min
- Learn 10 min
- Lab 15 min
- Quiz 10 min
- Exam 10 min
The messy bookshelf
A book's chapters are spread across five different shelves. How long does it take to read it compared with having it all together?
Reveal
Much longer: you keep walking between shelves. Files on a hard disk get split up the same way (fragmented). Defragmentation puts the pieces back together so the disk reads them faster.
Three utilities
Utility software is system software that helps maintain the computer and keep it running efficiently and securely.
Encryption software
Scrambles data using a key so it can't be understood without the key to decrypt it. Protects data if a device is lost or stolen.
Defragmentation
Reorganises a magnetic hard disk so the parts of each file are stored next to each other, and free space is grouped together. Files load faster because the read/write head moves less. Not needed for SSDs.
Data compression
Reduces the size of files so they take up less storage space and are quicker to transmit, e.g. zipping a folder before emailing it.
Defragment the disk
Which utility?
Exam-style questions
1. Explain how defragmentation can improve the performance of a computer.
[3 marks]Mark scheme
- Over time, files become split into parts stored in different places on the disk (1)
- Defragmentation moves the parts of each file so they are stored together / groups free space together (1)
- so the read/write head moves less and files are accessed faster (1)
2. Explain why defragmentation is not needed on a solid state drive.
[2 marks]Mark scheme
- An SSD has no moving parts / read-write head (1)
- so accessing data in different locations takes the same time / defragmenting would cause unnecessary wear (1)
TUTOR NOTES
- Misconception: defragmentation creates more space. It reorganises existing data.
- Misconception: compression software is an application. It's a utility.