The shape of the lesson
By the end of the lesson, learners can
- Why have an OS?: A bare computer is just hardware that obeys machine code.
- Five management tasks: The syllabus names five areas.
- Which task is it?: Exam questions often describe an event and ask which management task deals with it.
- Why an OS: hides hardware complexity, provides an interface, a platform for applications, and shares resources.
- Memory and process: RAM allocation and protection; scheduling processor time.
- File and security: directory structure and file operations; accounts, passwords, access rights, firewall.
- Hardware: device drivers, interrupts, buffers and queues for input/output.
One picture every idea returns to
An operating system (OS) is system software that manages the hardware and resources of a computer and provides a platform and an interface so that users and application programs can use the computer without controlling the hardware directly. Its key management tasks are memory management, file management, security management, hardware (input/output/peripheral) management and process management.
Forty-five minutes, phase by phase
| Time | Phase | What happens in the room | Grouping |
|---|---|---|---|
| 0 to 5 min | Hook: predict | Open with the question in the title, The essential manager.. Without an operating system, every program would have to drive the hardware itself and fight other programs for memory and the processor. Put the figure on the board: it is the one picture every idea in the lesson returns to. | Whole class, then pairs |
| 5 to 13 min | Teach and check: Why have an OS? | A bare computer is just hardware that obeys machine code. | Whole class, then pairs |
| 13 to 21 min | Teach and check: Five management tasks | The syllabus names five areas. | Pairs |
| 21 to 30 min | Teach and check: Which task is it? | Exam questions often describe an event and ask which management task deals with it. Model the worked example Match the task on the board, one line at a time. Your turn: A user saves a report into a folder called Finance. Name the management task and describe one thing the OS does. | Mix-Pair-Share |
| 30 to 36 min | Check | The four Stage 1 questions from the student lesson, answered on mini whiteboards or by show of fingers. Re-teach the one most get wrong. | Individual, then whole class |
| 36 to 43 min | Plenary | The exam-style questions from Stage 2, one at a time: thirty seconds alone, then a random call. The feedback lines in the key give the examiner's wording. | Individual, random call |
| 43 to 45 min | Exit and homework | Set the worksheet below (6 questions, 19 marks). Learners self-assess against the objectives before they leave. | Individual |
Protect the parts that carry the learning
The sequence carries about fifty minutes of material, so the lab is driven by one student while the class predicts rather than explored freely. Times are a guide.
Protected: the check at 30 minutes. It is the only individual read on whether the key idea landed, and it is not cut.
Cut first if the build overruns: the last check in Which task is it?, never the check or the plenary.
In a 60 minute block: run worksheet questions 1 to 3 in class as a Rally Coach set and model both the hardest worked example and its check live.
Mix-Pair-Share
Students mix around the room until you call pair; they pair with the nearest classmate, discuss the prompt, then mix again. Three prompts of rising difficulty, three different partners.
The full structure, with its variations and the other twelve, is on the cooperative-learning page.
What to head off, and how
| Trap learners fall into | Teaching move that pre-empts it |
|---|---|
| "The OS lets the computer run" earns nothing. | Say what it provides: an interface for the user, a platform of services for applications, and management of the hardware and resources. |
| Do not mix up the tasks. | Allocating processor time is process management; allocating RAM is memory management. |
Why a computer needs an operating system: worksheet
6 questions, 19 marks. Written in the style of the papers; no past paper question is reproduced.
Explain why a computer system requires an operating system.
Identify four key management tasks carried out by an operating system.
Describe how an operating system carries out memory management.
Describe three ways the operating system carries out security management.
A user is downloading a large file while editing a video and printing a document. For each, identify the OS management task: (a) the printer receives the document a block at a time from a buffer (b) the video editor and the download both get processor time (c) the downloaded data is saved into the Downloads folder (d) the video editor is given extra RAM.
A student says: "Process management and memory management are the same thing because both are about running programs." Explain why the student is wrong.
Answer key and marking notes
- It provides a user interface so the user can communicate with the computer.
- It hides the complexity of the hardware: applications use OS services instead of controlling hardware directly.
- It manages resources (processor, memory, storage, devices) and shares them between programs and users.
- Memory management.
- File management.
- Security management.
- Hardware (input/output/peripheral) management. (Also accept process management; one mark each, up to four.)
- It allocates memory (RAM) to a process when it is loaded and de-allocates it when the process ends.
- It keeps track of which areas of memory are free and which are in use.
- It protects each process's memory so that one process cannot access or overwrite another's (and uses virtual memory if RAM is full).
- User accounts with a username and password, so only authorised users can log in.
- Access rights (permissions) that control which users can read, write or delete each file or folder.
- A firewall and automatic security updates to block unauthorised access and fix vulnerabilities.
- (a) Hardware (input/output, peripheral) management.
- (b) Process management.
- (c) File management.
- (d) Memory management.
- Process management schedules the processor: it decides which process runs on the CPU and for how long.
- Memory management allocates and protects RAM for each process: it decides where each process is stored in memory.
6 multiple-choice questions on this lesson
From the topic question bank. Assign them in the app for a marked score in your gradebook, or run the topic as a class game.
Which statement best explains why a computer system needs an operating system?
- AIt manages the hardware and resources and provides an interface and services so users and applications can use the computer
- BIt translates every application program into machine code before the program is run
- CIt stores all of the user's files permanently so they are not lost when the power is turned off
- DIt lets application programs control each hardware device directly, without any device drivers
A word processor and a web browser both appear to run at the same time on a single-core computer. Which OS management task makes this possible?
- AProcess management
- BMemory management
- CFile management
- DSecurity management
Which of these is part of memory management?
- APreventing one process from overwriting the area of RAM allocated to another process
- BDeciding which of the waiting processes is given the processor next
- CKeeping a hierarchical directory of file names and their locations on disk
- DHolding print jobs in a queue until the printer is ready for them
A student tries to open a teacher's mark sheet on the school network and is told access is denied. Which OS management task produced this message?
- ASecurity management
- BHardware management
- CProcess management
- DMemory management
Data is sent to a printer much faster than the printer can print it. Which action by the OS stops the processor being held up, and which management task is it part of?
- AStoring the data in a buffer and queue so the processor can continue other work: hardware management
- BGiving the printer process a higher priority so it finishes sooner: process management
- CSaving the document to a folder until the printer is free: file management
- DMoving the printer driver into virtual memory so it uses less RAM: memory management
A video editor crashes, but a music player running at the same time carries on playing normally. Which explanation is most accurate?
- AMemory management had given each process its own protected area of RAM, so the crash could not corrupt the music player's memory
- BFile management had saved the music player's files in a different folder, so the crash could not reach them
- CProcess management had stopped the video editor using the processor, so it could not crash the music player
- DSecurity management had given the music player a stronger password than the video editor
Quiz key
The OS manages hardware and resources, gives the user an interface and gives applications a platform of services. Translating programs is the job of a compiler or interpreter. Permanent storage is provided by secondary storage hardware; the OS only manages files on it. The OS actually stops applications controlling hardware directly, and it uses device drivers to talk to devices.
Process management schedules processor time between processes, switching quickly so both appear to run at once. Memory management allocates RAM, not processor time. File management organises stored files, and security management controls accounts and access rights.
Memory management allocates RAM to processes and protects each process's memory from the others. Choosing the next process for the CPU is process management. A directory of files is file management, and a print queue is hardware (peripheral) management.
Checking a user's access rights against a file's permissions is security management (access rights also feature in file management). Hardware management deals with devices and drivers, process management with processor time, and memory management with RAM allocation.
The OS holds the data in a buffer (and print jobs in a queue) and the printer takes it at its own speed, so the CPU is free: this is hardware (input/output) management. A higher priority would make the CPU spend more time on printing, not less. Saving to a folder does not send the data to the printer. Moving a driver into virtual memory would slow it down and does not solve the speed mismatch.
Because memory management protects each process's memory, a failing process cannot overwrite another's code or data. Folders hold files on disk, not the running program in RAM. Process management shares processor time but does not by itself keep one program's data safe from another. Passwords belong to users, not to running programs.
Slides for this lesson
A projectable deck for every pack is on the way. Until then, present the student lesson full screen: its sections, figure and lab tabs follow the same order as the plan above.