Compt Sc Flashcards
Von Neumann Bottleneck
CPU is a lot faster than data/instruction transfer between it and RAM, so a lot of time is wasted by CPU just waiting for data/instructions to arrive after processing.
Effect minimised by Harvard.
Control Unit
Manages communication between other PC components
Manages the FDE cycle
Arithmetic Logic Unit
Performs arithmetic and logical operations.
Registers
Store temporary data while instructions are executed.
Cache
Store frequently used instructions or data.
Buses
Transfer control signals, data or addresses between components.
Serial Access
Data is accessed/stored in chronological order.
Sequential Access
Data is accessed/stored in some order (alphabetical, ascending…)
Indexed Sequential Access
Records have indexes associated with them in a table, which point to their location in memory where the fields are stored sequentially.
Random/Hash Access
A hashing algorithm output for a given record/field is the address in memory where it is stored.
- Calculation done on data in [KEY FIELD]
- Collision are two same memory addresses calculated by alg. for diff. data.
- Overflow areas/serial files are needed
- May be too slow
- Re-hashing needed
Sequential
Master file is copied field-by-field into a new file while the transaction file’s changes are appended into the new file in sequence.
Output is two master files, one backup, one new
Direct Access
Transaction file is appended onto the end of the master file.
Recommended to make a backup of the old master fiel beforehand for a backup.
Backups
A redundant copy of recent data made frequently.
Important to make periodic backups in case data is lost and relatively recent data can be used instead.
Can be generational (grandfather-father-son, three separate backups are made periodically.) and full, differential or incremental (whole, difference from last whole, difference from last). Exists in case one is corrupted.
Can be made on magnetic tape, cloud storage. On-site or off-site.
Archiving
Archival data, such as old software systems or out-of-data, is stored in case it becomes useful in the future.
Procedural Programming
Step-by-step instructions followed.
Algorithm carries out calculations or other actions.
Each step is controlled tightly.
Mark-Up Programming
Defines the structure and formatting of text files when viewed for presentation.
HTML (used in tandem with JavaScript to create dynamic sites)
Tags used.
Feasibility Study
Investigation made on a project before anything else to find whether it is feasible.
Feasibility Study - Technical
Are enough resources available?
Are developers skilled enough?
Feasibility Study - Economical
Does the project fall within budget?
Will a profit be made?
Feasibility Study - Political
Is the project controversial?
Would integrity be compromised?
Feasibility Study - Legal
Does the project comply with legistlation?
Feasibility Study - Operational
Will the project solve the problem?
Feasibility Study - Scheduling
Can the project be done within a reasonable time?
Design Analysis - Investigation and Analysis techniques
Reading documentation - Find current data flow and data structure layout
Questionnaire/Interview - Find out improvements or properties of the system from the stakeholders. (Questionnaire if distributed over large area, interview if specific people w/ lot of info)
Observing - Find out how the current system is being used by the stakeholders directly. they may not be entirely honest.
Research - Desktop searching for similar systems in order to discover inputs/outputs, data structures used, data flow, processing.
Design Analysis - Design
Input/Output
Data Structures & Methods of Access
Processing Methods (algortihms used)
Design Analysis - Testing
Unit - Each unit of the software is tested individually to evaluate valid inputs and outputs.
Integration - Units are connected and their interaction is tested.
System - The software system as a whole is tested. Includes Alpha and Beta (end-user) testing.
Acceptance - The system is evaluated for its compliance with the user’s requirements.
Design Analysis - Testing test data
Typical, extreme, erroneous
Design Analysis - Changeover
Direct - The old system is immediately exchanged for the new.
Parallel - The old and new systems are run in tandem until the organisation is confident to remove the old one.
Pilot - The new system is introduced in only one branch and is rolled out everywhere later.
Phased - Parts of the new system replace the old over time.
Design Analysis - Maintenance
Perfective - New features are added or performance is improved.
Adaptive - Changes made to suit new user requirements.
Corrective - Error patching and bugfixing.
Design Analysis - Documentation
User - Instructions on how to use the system for the users.
Maintenance - Details on the workings of the software system for IT staff, including variable lists, algorithms, inputs and outputs, data flow, data structures.
Contingency Plans
Before - Risk analysis and staff training
During - Staff response, contingency plan carried out
After - Backups retrieved and new hardware/software issued, recovery measures.
Utility Software
Antivirus
Backups
Compression
Defragmentation
Firewall
Resource management
Storage Devices (FAT & NTFS)
Input and output (devices)
Main memory (virtual memory)
Processing (seamless)
Misc. Hardware (drivers)
FAT & NTFS
File Allocation Table - Uses a linked list data structure to store data on a hard drive. Better for non-windows systems.
New Technology File System - Faster as it uses more complex data structures.
Off-the-shelf software
Cheaper
Available immediately
Low risk of not being functional
Community support
Bespoke software
Tailored to your needs
Flexible
Competitive advantage
Not tied to a vendor
Economic Impacts
Saving paper
Communication cost cuts
More efficient
More accuracy and precision
Ethical/Moral Impacts
Invasion of privacy
Data misuse
Copyright breach
Inappropriate content
Cultural Impacts
More access to information
World-wide communication
Digital divide
GDPR
General Data Protection Regulation
In relation to data, indivduals have the right to:
Relevant and adequate [1]
Accurate and up-to-date. [1]
Stored for no longer than necessary, [1]
Individual can check if being held securely. [2]
Processed under legistlation, [1]
As well as with limited function. [1]
CMA
Computer Misuse Act
Makes it illegal to:
1. Unauthorised access to a computer
2. Unauthorised access to a computer with intent to facilitate crime
3. Unauthorised access to a computer with intent to cause damage
FIA
Freedom of Information Act
Makes it possible to:
- Authorities must release information about certain activities to the public
- The public is entitled to request information from the authorities
RIPA
Regulation of Investigatory Powers Act
Makes it legal for organisations to obtain the right to survey and collect digital communications. Police and defense services.
CDPA
Copyright, Designs and Patents Act
In relation to software, art, books, films, music etc, makes it illegal to:
Make copies
Distribute copies (sell/publish)
Field
An attribute of an entity
Record
An iteration of an entity
Primary Keyfield
Unique identification field of each record
Flat File
Data that isn’t organised and has no relationships. Introduces data redundancy and inconsistency.
Relational Database
Data that is organised and has relationships between entities. This reduces data redundancy and data inconsistency.
Entity
A model of a real-life concept (abstract or physical).
Procedural
Is sequential
Uses iteration and selection
Executes instructions in the order they are written
Algorithms are written using it
Declarative
User defines a set of rules (facts and relationships between them).
User poses a task and program decides if the task can be completed and how.
Wolfram
Mark-Up
Defines the way text is interpreted by a browser.
Describes the visual formatting of the text using tags.
HTML in tandem with JavaScript
Visual
Allows user to drag-drop simple functions.
Learning tool, but unhelpful for advanced problems.
Event-Driven
Program sits in a ‘program loop’, waiting for user input.
Once user input is detected the program will activate a function.
Used for GUIs/games.
Object-Oriented
Non-linear programming that uses classes, templates of real things.
An object of a class creates an instance (the variable that stores all the data about the object in memory)
A class can have attributes and methods to describe it.
Used for data analysis/machine learning
OOPs - Concepts
Encapsulation -
Idea that data is grouped into classes rather than allowing it to stand individually. This improves flexibility and functionality.
Inheritance -
Some classes may be grouped together as ‘parent’ and ‘child’ classes. Child classes share the attributes and methods of the parent class. This reduces redundancy of code.
Internet
World-wide communications infrastructure.
IMAP
Instant Message Access Protocol
Allows users to view email messages from any device, accessing a server with their messages.
SMTP
Simple Message Transfer Protocol
Allows users to send email messages to another server over a network.
HTTP/S
Hyper-Text Transfer Protocol / Secure
Allows users to view websites and transfer information over a network.
FTP
File Transfer Protocol
Allows users to download/upload files of data over a network.
TCP/IP
Transfer Control Protocol / Internet Protocol
Sets up a connection between two devices over a web of networks (TCP)
Assigns a sender and destination address to packets. (IP)
UDP
User Datagram Protocol
Sets up a faster connection between two devices over a web of networks with no error checking (packets can be lost).
VOIP
Voice Over Internet Protocol
Allows users to make audio calls over networks.
DHCP
Dynamic Host Configuration Protocol
Dynamically assigns IP addresses to devices on a network.
SSL
Secure Socket Layer
Adds an extra layer of security and authentication to internet communications.
TCP/IP 5 Layer Stack
Application - Provides the interface between the network and software the user is using, i.e allows software to send and receive data which it can then meaningfully present to the user. (HTTP/S, FTP, SMTP)
Transport - Divides data into suitable packets and sets up a reliable connection between two devices. (TCP, UDP)
Network - Assigns sender and destination addresses to packets and manages flow control. (IP)
Data-Link - Converts packets into frames and relays them from the network layer to the physical layer.
Physical - Manages a reliable physical connection between the two devices over a suitable medium like cables, fiber optics, radio waves etc. (Ethernet, WiFi)
Packet Contents
Header:
Source and destination addresses
Packet sequence number
Total packet number
Protocol
Checksum
Payload:
The actual data
Masking
Masking determines the value of a bit at a specific location. (clearing, setting, inverting)
Serial & Parallel Transmission
Serial, transmits data one bit at a time through a single connection. USB, allows for further distance transmission & cheaper, but is slower.
Parallel, transmits data a whole number of bytes at a time (8bits,16bits…) as devices are connected by numerous serial connections. VGA, is faster, but has issues like crosstalk and skew at high bitrates.
Compilation Process
Lexical Analysis - Whitespace and comments are removed from the code.
Symbol Table - Variables, constants and identifiers are replaced with tokens. Metadata about them (data types, variable scope) is organised into a table.
Syntax Analysis - Tokens are checked for proper grammar and spelling as determined by language standards. If errors are found, a suitable message is produced.
Semantic Analysis - Variables are checked for proper declaration, data type and operations.
Code generation - High level language is converted to machine code.
Optimisation - Remove redundant code to make compiled program more efficient.
Compression Techniques
Compression is used to decrease the storage size of files.
Lossy:
Lossy compression causes some permanent data loss/decompression doesn’t return original file.
So not a viable choice for text files.
Used for video and audio (MP3 & JPEG)
Threshold truncation - A level is chosen beyond which data is truncated (removed), for example removing frequencies humans can’t hear in audio.
Lossless:
Decompression returns original file. (PNG)
Run-Length encoding - Repeated sequences of bits are stored as the bit times the number it is repeated by. (0000 = 0x4)
Dictionary encoding - Frequently used sequences of bits are stored in a dictionary file along with a key which is referenced on every use of its associated bit pattern.
IDEs - Writing
Editor
Statement completion
Syntax highlighting
Syntax checking
Automatic formatting
Optimisation
Linker
Loader
IDEs - Debugging
Debugging - Shows the exact line where an error is detected
Interpreter - Translates code into machine code line by line.
Compiler - Translated code into an executable file.
Break points - User can choose specific points at which to pause the program.
Stepping - Skip to a certain section of the code.
Variable watch - Allows user to view the current value of a variable.
Trace - Logs how the values of variables change as the program runs.
Emulator - Provides users with ability to test programs in different environments (OSs).
Memory inspector - Shows a section of RAM and details on how the program uses it.
Software System Uses
Weather forecasting - Take in lot of input from orbital satellites, Process a lot fo data, Analyse data and produce useful outputs (numerical data, visual data like heatmaps.), Function in real time.
Robotics - Interpret stimuli accurately, perform a series of tasks repetitively, move/rotate in necessary directions, use energy conservatively.
CAD - Greater accuracy and precision in drawing blueprints, 2D and 3D modelling possible, can be viewed from any angle, pre-made libraries of models available.
CGI - Simulate physics, provide user with creative tools, high-quality rendering of scenes, 2D & 3D animation.
Multiplexing
Parallel transmissions can be ‘muxed’ together into one serial transmission to give it all the advantages of serial data transport. This can be done via Frequency-Division Multiplexing. It is then ‘demuxed’ into parallel connections again.
CD Burning
CDs and DVDs encode data using a laser which burns indents.
The absence of a laser burn results in lands.
Burnt in a spiral pattern starting from the middle.
Packet & Circuit Switching
Circuit switching: A constant connection is estabilished between the two devices over which they exchange data. If it is interrupted, the connection disconnects and the two devices must connect via a different path. When there is an active circuit connection, no other data can be transmitted through it,
Packet switching: Dynamic path is estabilished over which data is sent in packets which are reassembled at their destination. Packets are difficult to intercept and interpret.
Data Representation
Integer - Short, 16 bits / Long, 32 bits
Real - Single Precision, 32 bits / Double Precision, 64 bits
Boolean - 1 bit
Character - Depends on the character set (7 or 8, 16 or 31)
String - Depends on the character set x length
Integer Vs Floating Point
Integer
Allows for exact representation of 0.
Less storage space
Faster processing
Flt Point
Larger range
More precision
Can store whole and real numbers
OS Modes of Operation
Batch Processing - Allows for processing of repetitive operations without user interaction. Performs during off-hours, stores errors for later and doesn’t pause.
Real-Time Control - Allows for near-instantaneous control of functions. Used for critical operations like nuclear power plant controls or plane ticket reservations.
Real-Time Transmission - Allows for near-instantaneous communication between users. Live-chat on apps like Whatsapp.
Expert Systems
Knowledge base
Rule base
Inference engine
User interface
