State three resources an operating system manages.

It manages the processor, main memory and the backing store, along with the attached peripherals.

Explain what is meant by calling the operating system a resource manager.

The operating system owns the machine's limited resources and decides which program gets each of them, for how long, so that all of them make progress without conflict.

Describe what happens when a computer is switched on, before the operating system is running.

A small bootstrap program held in read-only memory runs first, and its job is to load the operating system from backing store into main memory and hand control to it.

WJEC AS-Level Computer Science 601-5345-3

Hardware: Architecture, Memory and Storage

Topic overview Components of a computer system and how they connect Von Neumann architecture and the CPU The fetch-execute cycle Memory and caching Parallel processing Input and output devices and their uses Secondary storage, fragmentation and defragmentation

Networks and Data Transmission

Topic overview Serial and parallel transmission Simplex, half duplex and full duplex Multiplexing and switching Packets and the TCP/IP protocol stack Networks, standards and protocols Collisions and shared media Routing, addressing and the internet

Logic Gates and Boolean Algebra

Topic overview Logic gates and their truth tables Boolean notation and expressions Building and reading truth tables Boolean identities and rules Simplifying Boolean expressions De Morgan's laws Masking and clearing registers

Data Representation and Data Types

Topic overview Bits, bytes and words The binary number system Hexadecimal notation Character sets and storing characters Primitive data types and storage requirements Binary arithmetic and negative numbers Real numbers, truncation and rounding

Data Structures

Topic overview Data structures and data types One-dimensional arrays Two-dimensional arrays Manipulating arrays Records and fields Arrays of records Choosing a data structure

Organisation of Data: Files and Records

Topic overview Files, records and fields Fixed and variable length records Master and transaction files File access and organisation methods Sequential file access and update algorithms File security, backup and archiving Data validation and verification

Database Systems

Topic overview Flat files and the relational model Relational and other contemporary database systems Primary, foreign, composite and candidate keys Indexes and links between tables Entity relationship modelling Normalisation to third normal form The database management system, queries and user views

The Operating System

Topic overview The need for an operating system The kernel and process management Memory protection and the backing store The user interface between user and hardware Directory structures and file attributes Utility software Batch, real time control and transaction processing

Algorithms and Programs

Topic overview Defining and designing algorithms Variables, constants and identifiers Scope, subprograms and parameter passing Sequence, selection and repetition Mathematical and logical operations Standard algorithms: sorting, searching and compression Dry running, trace tables and test data

Principles of Programming

Topic overview Procedural programming Event-driven and visual programming Mark-up languages Object-oriented programming: objects, classes and methods High-level languages Low-level languages Choosing a language for a problem

Systems Analysis

Topic overview The systems life cycle and the feasibility study Methods of investigation Analysis, abstraction and decomposition Design and data flow diagrams Testing and changeover Maintenance Backup, recovery and documentation

Software Engineering and Program Construction

Topic overview Integrated development environments and their purpose Editors, syntax highlighting and code entry tools Debugging tools: breakpoints, stepping and watches Translation, source code and object code Lexical analysis and the symbol table Syntax and semantic analysis Code generation and optimisation

Types of Software System

Topic overview Off-the-shelf, bespoke and custom software Open source and proprietary software Computers in weather forecasting Computer aided design and manufacture Robotics in industry Computer generated graphics and animation Expert systems

Practical Programming

Topic overview Designing data structures: fields, records and data types Key fields and methods of access Validation of input data Designing routines with pseudocode Tracing code and test data Prototyping and evaluating a solution Annotated listings and readable code

Data Security and Integrity

Topic overview Dangers of holding files of personal data Levels of permitted access and access control Passwords and authentication Clerical procedures and write-protection Threats to computer systems Malicious and accidental damage to data Contingency planning and disaster recovery

Computing, Society and the Law

Topic overview Social and economic change from computing Computers and the nature of employment The digital divide and cultural change Environmental cost of computing Data protection and freedom of information law The Computer Misuse Act 1990 and computer crime Copyright, surveillance and professional codes

The Operating System

7 subtopics
21 things to know
AS Unit 1

What The Operating System covers

The Operating System is examined in AS Unit 1, Fundamentals of Computer Science. It covers the need for an operating system, the kernel and process management, memory protection and the backing store, the user interface between user and hardware, directory structures and file attributes, utility software and batch, real time control and transaction processing.

Where it is assessed

AS Unit 1

Fundamentals of Computer Science, examined again at A2 at a more demanding level.

Check the WJEC specification ↗

The 7 subtopics

Each one has its own page. WJEC AS Computer Science students sit this topic in the first year.

What you need to know

Answer each one before you reveal it.

Your recallNot started

Key term

Why must a virus signature database be updated frequently?

Key term

Contrast the urgency of a real time control system with that of a real time transaction system.

Key term

What is an operating system?

Key term

What is the kernel of an operating system?

Process

Why must one process be stopped from writing into another process's memory?

Key term

Why does the operating system provide a user interface?

Key term

What is a directory?

Key term

Why does a computer need an operating system rather than each program controlling the hardware itself?

Process

What is a process?

Key term

What happens when a program attempts to access an address outside the area allocated to it?

Key term

What is a command line interface?

Key term

Explain what is meant by a hierarchical directory structure.

Key term

How does utility software differ from an application?

Process

State two features of a batch processing system.

Key term

Why can a program written for one operating system usually not run on a different one?

Process

Explain how a computer with one processor appears to run several programs at the same time.

Key term

What does the operating system do with the memory a program occupied once that program ends?

Key term

State two drawbacks of a command line interface.

Key term

What is a subdirectory?

Key term

Name four utility programs.

Process

Give two applications well suited to batch processing.

Take The Operating System further

The same content, four other ways.

Questions from this topic

Each one with the model answer underneath.

1
What is an operating system?
Model answer
An operating system is the system software that controls the hardware, allocates its resources to programs and provides the interface through which the machine is used.
2
Why does a computer need an operating system rather than each program controlling the hardware itself?
Model answer
Every program would otherwise need its own code for every device, and two programs claiming the same device or the same memory at once would corrupt each other's work.
3
State three resources an operating system manages.
Model answer
It manages the processor, main memory and the backing store, along with the attached peripherals.
4
Explain what is meant by calling the operating system a resource manager.
Model answer
The operating system owns the machine's limited resources and decides which program gets each of them, for how long, so that all of them make progress without conflict.
5
Describe what happens when a computer is switched on, before the operating system is running.
Model answer
A small bootstrap program held in read-only memory runs first, and its job is to load the operating system from backing store into main memory and hand control to it.
6
Why can a program written for one operating system usually not run on a different one?
Model answer
The program calls on that operating system's own services to reach the hardware, and a different operating system offers those services under different names and rules.

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Hardware: Architecture, Memory and Storage

Networks and Data Transmission

Logic Gates and Boolean Algebra

Data Representation and Data Types

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Fetch, , execute.

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AEncryption is reversible.

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Assemble a full-mark answer from its marking points, in the order an examiner wants them.

A bit is a single binary digit.

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Short focus games to reset attention, so the next set lands better than the last.

The Operating System revision questions

Is The Operating System examined at AS in WJEC Computer Science?: Yes. It sits in AS Unit 1, which you take in the first year, so it is on the AS paper as well as counting towards the full A level.
What does The Operating System cover in WJEC AS-Level Computer Science?: 7 subtopics: the need for an operating system, the kernel and process management, memory protection and the backing store, the user interface between user and hardware, directory structures and file attributes, utility software and batch, real time control and transaction processing. Each one has its own page with questions and model answers.
How is The Operating System organised?: By the WJEC 601-5345-3 specification, subtopic by subtopic, so it matches the order you are taught it in.

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