What does the address bus carry, and in which direction does it operate?

The address bus carries the memory address that the processor wants to read from or write to. The address bus is unidirectional.

Why is the data bus bidirectional?

The data bus is bidirectional because data travels from memory to the processor and back again. Instructions and operands both travel along the data bus.

What kind of signals does the control bus carry? Give two examples.

The control bus carries timing and command signals that coordinate the rest of the machine. Two examples are the memory read signal and the clock signal.

Eduqas A-Level Computer Science A500QS

Data Structures: Arrays, Records and Hash Tables

Topic overview One-dimensional arrays and indexing Two- and three-dimensional arrays Manipulating arrays: insertion, deletion and searching Records and fields Arrays of records and record manipulation Hash tables, hashing and collisions Choosing and justifying a data structure

Stacks, Queues, Linked Lists and Trees

Topic overview Stacks: push, pop and the stack pointer Implementing a stack in an array Queues: enqueue, dequeue and pointers Circular queues and priority queues Linked lists: nodes, pointers and the free list Binary trees: nodes, roots and leaves Traversing linked lists and trees

Boolean Logic and Simplification

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Algorithms, Pseudo-Code and Programming Constructs

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Variables, Scope, Parameters and Identifiers

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Recursion and Modular Programming

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Sorting Algorithms

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Searching and Shortest-Path Algorithms

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Big O Notation and Algorithm Efficiency

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Validation, Verification and Testing

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Data Compression

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Programming Paradigms and Computer Languages

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Systems Analysis, Maintenance and Documentation

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System Design and Human-Computer Interaction

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Software Engineering Tools and Translators

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Computing, Society and the Law

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Computer Architecture, the Processor and Assembly Language

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Input, Output and Secondary Storage

Topic overview Input devices and how data is captured Output devices and how results are presented Choosing input and output devices for a situation Voice input, dictation and voice print recognition Magnetic, optical and solid state storage Comparing secondary storage for a purpose Disc organisation, fragmentation and defragmentation

Networks, Protocols and the Internet

Topic overview Networks, LANs and WANs Network topologies and connection hardware Networking standards and the layered model IP addressing, TCP and UDP Application protocols: HTTP, FTP, SMTP, IMAP and DHCP Handshaking and establishing a connection Wireless hardware and wireless technologies The internet and connected mobile devices

Data Transmission and Network Performance

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Number Systems and Binary Arithmetic

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Data Types, Characters and Floating Point

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Files, Records and File Organisation

Topic overview The purpose of files in data processing Files, records and fields Fixed and variable length fields and records Master files and transaction files Serial and sequential file access Indexed sequential access and multi-level indexes Direct access and hashing algorithms Overflow handling and file reorganisation File security, backups, generations and archiving

Databases, Normalisation and Entity Modelling

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SQL, Big Data and Distributed Systems

Topic overview Query languages and the purpose of SQL Creating tables: CREATE TABLE, data types and keys Retrieving data with SELECT, FROM and WHERE Comparison operators, IN, AND, OR and sub-queries Sorting, grouping and aggregate functions Inserting, updating, deleting and joining data The DBMS, the data dictionary and distributed databases Big Data, data warehousing, data mining and predictive analytics

The Operating System and Its Modes

Topic overview The need for an operating system and the role of the kernel Managing peripherals, processes and memory protection The user interface and the layers between user and hardware Directory structures and file attributes Utility software Batch processing, real time control and real time transaction systems Types of operating system: single-user, multi-user, multi-tasking and multi-programming Designing an interface for different users and environments

Interrupts, Memory Management and Scheduling

Topic overview What causes an interrupt Interrupt handling and the interrupt service routine Interrupt priorities and how they are allocated Partitioning main memory Methods of data transfer between processor and devices Buffers and double buffering High level scheduling, processor and device allocation Process states, time-slicing, polling and threading

Types of Software System

Topic overview Open source, bespoke and off-the-shelf software Safety-critical systems Computers in weather forecasting Computer aided design and computer generated graphics Robotics and automation Control systems Expert systems The internet, intranets and search engines

Data Security, Cryptography and Attack

Topic overview Online updating and the integrity of shared files Dangers of holding personal data Clerical procedures, access levels, passwords and write protection Cryptography: its purpose, and symmetric and asymmetric keys Hashing, digital signatures and certificates Caesar and Vernam ciphers and comparing cipher strength Biometric technologies and their limitations Threats, damage and contingency planning Malicious software, hacking and penetration testing

Computer Architecture, the Processor and Assembly Language

Hardware elements and how they are connected

3 things to know
Component 2

Overview

Four main hardware elements of a general-purpose computer system, bus in a computer system and three buses that make up the system bus.

What you need to know

Answer each one before you reveal it.

Your recallNot started

Key term

What are the four main hardware elements of a general-purpose computer system?

Key term

What is a bus in a computer system?

Key term

Name the three buses that make up the system bus.

Questions from this subtopic

Each one with the model answer underneath.

1
What are the four main hardware elements of a general-purpose computer system?
Model answer
The four elements are the processor, main memory, secondary storage and input/output devices. Buses connect them all together.
2
What is a bus in a computer system?
Model answer
A bus is a set of parallel wires carrying signals between components. Each wire carries one bit at a time.
3
Name the three buses that make up the system bus.
Model answer
The system bus is made up of the address bus, the data bus and the control bus. All three connect the processor to memory and to input/output controllers.
4
What does the address bus carry, and in which direction does it operate?
Model answer
The address bus carries the memory address that the processor wants to read from or write to. The address bus is unidirectional.
5
Why is the data bus bidirectional?
Model answer
The data bus is bidirectional because data travels from memory to the processor and back again. Instructions and operands both travel along the data bus.
6
What kind of signals does the control bus carry? Give two examples.
Model answer
The control bus carries timing and command signals that coordinate the rest of the machine. Two examples are the memory read signal and the clock signal.

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