What is a register, and why is it faster than main memory?

A register is a very small store holding one word inside the processor itself. A register needs no bus transfer, so the processor can read it in a single clock cycle.

What does the program counter hold?

The program counter holds the address of the next instruction to be fetched. The program counter is incremented during each fetch.

What does the memory address register hold?

The memory address register holds the address of the memory location currently being accessed. The memory address register drives that address onto the address bus.

What does the memory data register hold?

The memory data register holds the data or instruction just read from memory, or the value about to be written to memory. The memory data register is the processor's gateway to the data bus.

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

Topic overview AND, OR and NOT truth tables XOR, NAND and NOR truth tables Truth tables for combined Boolean expressions Boolean identities and rules De Morgan's laws Simplifying Boolean expressions Logical operators in programs, masking and encryption

Algorithms, Pseudo-Code and Programming Constructs

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Variables, Scope, Parameters and Identifiers

Topic overview Variables and constants Self-documenting identifiers Annotation and program layout Scope of variables: local and global Lifetime of variables Procedure calling, parameters and return values Call by value and call by reference

Recursion and Modular Programming

Topic overview Recursion and the base case How recursive calls use the stack Recursive algorithms: factorial and Fibonacci Recursion compared with iteration Integer division with DIV and MOD Standard functions and standard modules User defined subprograms and modular design

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

Topic overview Waterfall, Agile and approaches to systems development The feasibility study, budgets and time scales Methods of investigation Abstraction, decomposition and data flow diagrams Selecting suitable hardware and software Acceptance testing and methods of changeover Perfective, adaptive and corrective maintenance Backup and recovery procedures User and maintenance documentation

System Design and Human-Computer Interaction

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Software Engineering Tools and Translators

Topic overview Software tools for the software engineering process Software packages in analysis, specification, design and testing Integrated development environments Debugging tools Program version management Compilers, interpreters and assemblers The stages of compilation Translation errors and execution errors

Computing, Society and the Law

Topic overview Social and economic change from computing Moral and ethical consequences Cultural change and the digital divide Codes of conduct and professional behaviour The effect of computers on employment Data protection and privacy law Computer misuse, copyright and freedom of information

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

Topic overview Serial and parallel transmission Simplex, half duplex and full duplex Multiplexing and sharing a channel Circuit, message and packet switching Packets, headers and packet contents Network collisions and collision detection Routing traffic on a network Calculating transfer rates and lowest cost routes

Number Systems and Binary Arithmetic

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Data Types, Characters and Floating Point

Topic overview Primitive data types Storage requirements for each data type ASCII and standardised character sets Unicode and multilingual encoding Floating point form: mantissa and exponent Converting between real numbers and floating point Integer and floating point compared Truncation, rounding and accuracy

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

Topic overview Data consistency, redundancy and independence Relational databases and other database models Primary keys, foreign keys and indexes First normal form Second normal form Third normal form Entity relationship modelling User views and turning data into information

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

The processor: control unit, ALU and registers

3 things to know
Component 2

Overview

Role of the control unit, status register and general purpose register and a special purpose register.

What you need to know

Answer each one before you reveal it.

Your recallNot started

Key term

What does the control unit do, and what does the arithmetic logic unit do?

Key term

What is the role of the control unit?

Key term

What operations does the arithmetic logic unit carry out?

Questions from this subtopic

Each one with the model answer underneath.

1
What is the role of the control unit?
Model answer
The control unit decodes each instruction and sends timing and control signals to the rest of the processor. The control unit also directs the flow of data along the buses.
2
What operations does the arithmetic logic unit carry out?
Model answer
The arithmetic logic unit performs arithmetic such as addition and subtraction. The unit also performs logical operations such as AND, OR and NOT, and bit shifts.
3
What is a register, and why is it faster than main memory?
Model answer
A register is a very small store holding one word inside the processor itself. A register needs no bus transfer, so the processor can read it in a single clock cycle.
4
What does the program counter hold?
Model answer
The program counter holds the address of the next instruction to be fetched. The program counter is incremented during each fetch.
5
What does the memory address register hold?
Model answer
The memory address register holds the address of the memory location currently being accessed. The memory address register drives that address onto the address bus.
6
What does the memory data register hold?
Model answer
The memory data register holds the data or instruction just read from memory, or the value about to be written to memory. The memory data register is the processor's gateway to the data bus.

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Data Structures: Arrays, Records and Hash Tables

Stacks, Queues, Linked Lists and Trees

Boolean Logic and Simplification

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