toggles a subset of the bits in the value
when you use a 1 the bianry is toggled/ switched around and 0s there is no impact
Depth First algorithm
- PUSH the first node onto the stack
a. push each node onto the stack until a child node is reached
b. visit the node which is the lowest you can reach
c. if no node to visit pop off the stack
- Until stack is empty
Encryption is the process of encoding a message so that it can be read only by the sender and the intended recipient.
Serialisation ensures that transactions do not overlap in time and therefore cannot interfere with each other or lead to updates being lost
a template to set out a define what attributes an object of a certain type should have
how is redundancy used usefully
organisations build in redundancy e.g. duplicate hardware so that if the main system fails the backup can take over
do until loop pseudocode
do one statement after another in the correct order
Symmetric Encryption is when the same key is used to encrypt and decrypt the message. Both party’s must know the key and also keep it secret.
reverses the outcome of the expression
bit, nibble, byte, kilobyte, mega, giga, tera, peta, exa, zetta, yotta
Multiple by 1024 to move up
Method of capturing data (Manual)
Paper data capture form (read by OCR & OMR or typed in manually)
purpose of operating systems: managing external devices
Using device drivers to translate operating system instructions into those understood by specific models of hardware device
How are character sets used to represent text?
When character in the set has a corresponding binary value which is a set number of bits. These are stored in a sequence that represents a word etc.
Capacity of magnetic
640 GB - 1TB
synchronise the change of state of flip flop circuits
A list of data together with a set of links to sort the data. Data is stored in the order its input and pointers are used to link the data into the desired order.
do a set of statements based on conditions allow your code to make choices- otherwise known as branching
No central computer, all computers are connected to each other locally or over a WAN
disadvantages of Client-Server
- Can be expensive to set up and to manage
- Server is single point of failure
how to convert floating point binary to denary
1) First work out the denary number in the exponent which tells us that the binary point moves ‘n’ places to the right
2) Write out a new binary weighting line with the point in the right place and then convert into denary
components of a packet
senders address, recievers address, packet contents, sequence number
Any change in the database must retain the overall state of the database.
sequential circuit that changes state at regular time intervals
stores the address of the next instruction
Power of self test
in two’s complement the sign is stored in
the most significant bit
where the operand contains the address of the value to be used.
Asymmetric Encryption (Public Key Cryptography) is when a public key and a private key is used. The public key is used to encrypt the data and the private key is used to decrypt the data. If you use person X’s public key to encrypt the data only person X’s private key will be able to decrypt it
Advantages of networks
- allows sharing of data
- allows collaberative working
- good for communication
- allows sharing of resources e.g. printers, storage and scanners
- easy to backup to a central point
Real-time Operating system
Designed to carry out actions within a guaranteed amount of time even when left running for long period.
program code. Sequences of instructions which are executed in order to perform a task.
Client side processing
data is processed on client side and send back to the server. This is used for security as it avoids data transfers.
Disadvantages of the agile model
- Not suitable for quick projects
Current instruction register
stores the actual instruction that is being decoded
if condition then code elseif condition then code else code endif
size of the structure can change at runtime
Optical storage advantages
light weight and portable
As you follow code you note down when each variable changes and what each value is
the data is organised in a logical way
purpose of operating systems: managing the memory
allocating and managing the memory used and relinquished by processes using pages and segmentation. Managing virtual memory
constructor of a superclass
public procedure new(inputs)
attribute = input
a group of instructions that a computer can carry out. unique for computers.
(stages of compilation stage 4)
the code is optimised to run as fast as possible by removing redundant code (removing variables and procedures that have been written but never called)
Multiple CPUs working on a single computer
Once a process has entered the running state it can be stopped
Inheritance OO pseudocode
class Dog inherits Pet code endclass
A one directional bus that transmits memory addresses that are used as operands in programming instructions, so that data can be retrieved from main memory
XML (eXstensible Markup Language)
A markup language that uses tags to denote data
Methods of sending data
Electronic Data Interchange (EDI) - is the computer-to-computer exchange of business documents in a standard electronic format between business partners.
Application Programming Interface (API) - a prewritten set of subroutines that provide access to the
- A URL to a file
Complex instruction set computing, large number of instruction each taking multiple machine cycles to carry out.
used to synchronise operations
font size CSS property
Uses of real-time operating systems
Airline control, theatre bookings, heart monitors, production lines, radar systems
purpose of operating systems: providing networking
communication through protocols and other machines and devices
Once a change has been made to a database it must not be lost due to a system failure.
*, selects all the elements
are lists that cannot be edited, they are immutable
an array which is coupled together with a hash function.
stack data structure
A stack is known as a LIFO, a single pointer is used to point to the top item of the stack, when a new item is pushed onto the stack the pointer is incremented. When an item is popped off the stack the pointer decrements to point to the new top of the stack.
second normal form
- Check the data is already in 1NF
- Remove any partial dependencies
- ‘fix’ any many to many relationships you discover
Open Systems Interconnection 7 layer model
(7) Application Layer
(6) Presentation Layer
(5) Session Layer
(4) Transport Layer
(3) Networking Layer
(2) Data Link Layer
(1) Physical Layer
breaking down a problem into smaller sections
Server side processing
used to interact with permanent storage like databases or files. It also renders the pages to the client
where the order of data is maintained
how to do CSS in HTML
Data Protection Act parts
Data processed fairly and lawfully
Data should only be collected for specific purposes
Data should be relevant and not excessive
Data should be accurate and up to date
Data should not be kept longer than needed
The user has a right to access and correct data
The organisation must have suitable security
Data can not be transferred outside the UK to any country with no data protection laws
How is a stack used in a ISR
when an interrupt comes the current instruction is pushed onto the stack. Once the interrupt has finished it pops the instruction off the stack and processes it
protecting agaisnt hacking:
- Packet snifferes
- User access logs
variables contained within and associated to an object
checks that the hardware is connected is connected and working in what is known as a power on self test
The CPU checks with each device if it needs attention. Inefficient and wastes time as some devices will not want attention when called upon
how does arithmetic (signed) right shift work?
shift everything to the right and backfill the space with 1s
normalising a positive binary number
back fill with 0s
Input device examples
Key board Card readers Microphones Cameras Barcode scanners OMR/OCR Mice Sensors Magnetic stripe reader touch pads
Object Orientated language
coders develop a solution which consists of objects that have been modelled on the real worl.
A graph which has few edges in relation to vertices
uses flash memory so data is read and written directly to blocks and pages on the silicon micro-chips
a set of edges/arcs connecting vertices/nodes
<a> link text </a>
(4) Passes data to the physical network
transforms a string of characters in a record into a shortened form that can be used as a disk address
De Morgan’s Law
¬ (A∨B) = (¬ A) ∧(¬ B)
NOT (A OR B) is the same as (NOT A) AND (NOT B)
press key/click button with their foot to send signal.
any field in a database which is not a primary, candidate or foreign key. They are used to order queries.
bitwise shifts and masks
An intermediate representation which combines compiling and interpreting and is run by a byte code interpreter
an array containing one or more arrays.
Advantages of Using encapsulation
- reduces chance of error
- consistent changes
- prevents accidental changes
equal units of memory. each with separate memory addresses.
over time a disk becomes fragmented as old files are deleted and new files are added, free space often becomes scattered across a disk and a program has to be split and spread across a disk to fit. The more fragmented the slower the computer performs
a self-contained set of commands that can be called from different parts of the program.
Algorithm for insertion into a binary tree:
- If tree is empty enter data item at root and stop; Current node = root
- Else repeat:
a. If new data item is less than value at current node go left, else go right.
b. Current node = node reach (null if no node)
c. Until current node is null
- Create new node and enter data
different traversal methods
Coacial Copper Cables
older, slower and cheaper
node at the top of the tree
Chip Multi Processor (CMP)
a single chip which contains 2 or more independent CPUs which can execute independent instructions
border width CSS property
factors to consider when choosing applications (9)
speed does it provide the necessary functionality cost and pricing hardware requirements memory convenience is it well used, tried and tested is it available off the shelf or will it have to be hand written
The appropriate instruction/ opcode is carried out on the data/ operand
writing software and algorithms which appear to behave as if they were intelligent
What is a more complex data type called?
Star topology disadvantages
Can be expensive to set up because of the length of cable required
Central device is a point of failure
Uses of assymetric encryption
used for transfering data e.g. online shopping
basic Boolean operators
all attributes are dependent on..
the key, the whole key, and nothing but the key
height CSS property
all terminals have equal status and there is no powerful central server, each computer acts as both a client and a server.
when each computer on a network takes on part of a problem
Simple Mail Transfer Protocol – used by mail servers and clients to transfer email across the internet
illegal instruction encountered
new log-on request
Uses of CISC
what most desktops use, Intel or AMD
Benefits of circuit switching
- highly reliable
- once the circuit is set up communication is fast and generally error free
Drawbacks of circuit switching
- dedicated connection therefore even if the channel is free it cannot be used to transmit other data
- requires more bandwidth
- time is taken to determine the physical link before hand
blow/suck to send signal.
Buffer almost empty
buffer allows each device or process to operate without being held up by the other
receive and send electrical signals in a network.
partial key dependency
one or more f the attributes depends on only part of the primary key (if the primary key is a composite key)
Data integrity is the maintenance and consistency of data in a data store. The data store must reflect the reality that it represents.
internal storage examples
magnetic hard drive, ROM, RAM, internal solid state drive
Use of distributed operating systems
Data centres, large companies, weather/financial modelling, data mining trend finding
Output device examples
speakers plotters printers monitors actuators projectors LEDs
the size of the structure cannot change at run time
The value given is added to the valued stored in the index register to give the memory location.
What does a bitwise left shift do?
multiplies the number by 2.
Binary -> denary negative exponent
create an instance of a class OO
objectName = new className(parameters)
Breadth first algorithm
- PUSH the first node into the queue
- mark as visited
a. visit all unvisited nodes connected to the first node
b. push nodes onto the queue
- until all nodes visited
a. POP next node from queue
i. visit unvisited nodes connected to current node
ii. PUSH nodes onto quue
c. until all nodes visited
- until queue empty
Absorbtion Law OR
A∧(A∨B)=A X AND (X OR Y) is the same as X
procedural languages examples
Pascal, C, Basic and Python
What is ASCII
- A character set
- Maps values to characters
- Uses 7-bits/ 8-bits per character
types of interrupts
A∧ ¬A =
Contemporary processor architectures
Modern high-performance CPU chips incorporate aspects of both Von Neumann and Harvard architectures
e.g. memory for both data and instructions but cache is divided into instruction and data and multiple parallel data buses
Sign magnitude most significant bit
represents + or -
+ = negative
- = positive
Hashing is the process used to transform a data item into something different. A hashing function provides a mapping between an arbitrary length input and a fixed length output. It is a one-way transformation meaning you cannot get back to the original form.
Memory read signal
causes data from the addressed location in RAM to be placed on the data bus
Bus request signal
indicates that the CPU has granted access to the data bus
when something appears in multiple forms and the program makes sure the correct meaning of a function is run
Inserting an item in a hash table:
- Feed in key to the hash function
- Go directly to the array index (HashValue)
- If the location is empty then insert the value
- Else follow the linked list in sequence until a free space in found and insert the value
the actual instruction
Open Source Software
any software which is supplied along with its original source code.
Drawbacks of closed source software
- costs money, can be expensive
- small range of versions of software
purpose of operating systems: managing security
servicing and denying requests to access the resources connected to the computer
Bottleneck address bus
the width of the address bus determines the maximum possible capacity of the system
Input devices for limited mobility
- Foot mouse/pedal
- Camera/eye tracker
- Puff/suck switch
an ordered data structure accessed through an index. the have no predefined scope and can be edited during run time.
Actual data is removed from the file in order to reduce its size. An algorithm is used to strip out the least important data. The original file cannot be restored as data is physically removed.
store data with no specific order meaning if data is added it is simply appended onto the end of the file. You cannot delete data from a serial file. good for storing simple data sets text files and configuration files.
commutation LAW OR
A∨B = B∨A
The order in which two variables are OR’ed makes no difference
purpose of operating systems: managing the processor
deciding which process to execute next and handling interrupts to the currently executing process
Half adder use
adds two bits
commutation LAW AND
A∧B = B∧A
The order in which two variables are AND’ed makes no difference
Binary -> denary positive exponent
+ exponent ->
the data to be transmitted is broke up into individual packets at the source computer. each packet is labelled with an address and sequence number. The packet is then forwarded onto the network and follows its own individual route. Depending on network traffic each packet will take different routes at different times to reach their destination where is is then reassembled.
Address bus average width
normalising a negative binary number
back fill with 1s at the high end and 0s at the low end
Possible uses of graphs:
- Navigation Systems
- Data Transmission
- Web page links
- Social media trends
Disadvantages of extreme programming
- Not suitable for programmers separated geographically
- Client must be able to commit to having full time contact with the programmers
a way to classify programming languages based on their features.
how to solve hash table collisions
- store the key in in the next available space
- combine with a linked list
The unnecessary duplication of data in a database
capacity of solid state
around 500 MB
Uses of virtual machines
- used on networks to avoid redundant processors
- translating code (Java)
- running different operating systems
an arrangement where ever node is connected to every other node.
Memory Data register (MDR)
stores the data which is to be sent or fetched from memory
moving the point to the left
relationship between high-level and assembly code
one to many
uses of a GPU
Will be present on a graphics card in a computer used in - Machine learning - Oil exploration - Image processing - Financial transactions
virtual storage disadvantages
Expensive if you want to store large amounts of data
Access times can be slow if there is poor internet connection
Cop Right Design and Patents Act
protects the intellectual property rights of individuals and organisations. This law makes it illegal to Copy, Modify or Distribute any software or any other intellectual property without permission of the original creator.
post order dot
one programmer types and another checks at the same time.
border style CSS property
the wires that connect a network
operates, controls and maintain the computer and its components.
Bitwise ANDing …
extracts a subset of the bits in a value
when the mask is a 1 it retains the value however when the mask is a 0 it outputs just 0s meaning only certain values are extracted.
main factors effecting CPU performance
number of cores
amount and type of cache
What do the nodes on a binary tree contain
left pointer, data, right pointer
Disadvantages of the spiral model
- Acknowledge user input
- Create prototypes to communicate to the user ideas better
- Better for small projects
general purpose application software
A software that can be used for many purposes e.g. word-processor
first in first out
has one or more edges that have an arrow indicating you can only go in one direction
many interconnected networks over many different countries via dedicated connections known as backbones
Embedded Operating Systems
embedded systems are often run on dedicated hardware so they run with maximum efficiency, with low powered processors and minimal memory
devices used to connect devices on a network, they use the physical hardware MAC address to send data on to the required destination node.
any device which is able to take data which is stored in a digital form and convert it into another format which wee can process e.g. sound, images or vibrations
drawbacks of assymmetric
- not as fast
gives the remainder of a division
three main class sections:
Recording Locking prevents simultaneous access to objects in a database in order to prevent updates being lost or inconsistencies in the data arising.
Multi-tasking operating system
one processor is scheduled so that each process receives a very small time slice of processor time giving the impression of them running simultaneously.
Application Programming Interface governs how two applications should interact
Adding data from linked lists:
- Store the data at the location indicated by the free storage pointer
- Alter the free storage pointer to the next free storage space
- Work out where in the list the new item should be inserted
- Set the pointer for the item that will precede it to the new data item
- Update the pointer for the new data item to that previously stored in the item the preceded it
5 most common primitive data types
integers, real (float), characters, string and Boolean
Removing data from linked lists:
- If the item to remove is in the first position
a. Then update starting pointer value of item you want to delete
b. Update all the pointers
- Else if the item is in any other position
a. Update the pointer value in the preceding node from the one you want to delete to the value of the pointer in the item to be removed
- Update the free pointers
structure and data can be changed at runtime
what connects different networks?
routers and gateways
Disadvantages of client side processing
- Not all browsers support all script
- Because the scripts are processed by the client, they are dependent on the performance of the clients’ machine
small programs each with a very specific purpose, which is normally concerned with the maintenance and wellbeing of a computer system
for loop pseudocode
for i=0 to 7
when both users try and access the database at the exact same time meaning neither can edit it
The text that will appear in the tab heading
linker (static linking)
includes links to any library code and place it in a single executable file. this is known as static linking and results in large programs because all the code is held in one file.
- A type of agile methodology, involving a user imbedded in the company to give feedback.
- This results in high quality code being developed quicker.
positive of the binary point is fixed on the number line
What loads the OS into RAM
a region of a physical memory storage used to temporarily store data while it is being moved from one place to another
purpose of operating systems: providing a platform for Software and utility programs
provides a framework for applications to run, allowing the to, for example, open and close files easily. The user can also interact with operating systems to manage files and use a range of utilities
a keyword, constant, variable, identifier or operator from the code
arcs on a tree
A relational database has more than one related table. It is more efficient that a flat file database as no data is duplicated meaning querying is easier.
uses of functions and procedures
breaking a problem into manageable sections
preventing duplicating sections of code when it is needed more than once in a program
Operating system (System software)
allows the user to control the computer with ease.
Provides a virtual machine hiding the true complexity of the computer from the user.
Manages and controls access to the computer’s resources.
normalising a number
means that there is only one way to represent the number
virtual storage advantages
data can be accessed anywhere so long as you have internet access
data can be easily shared between devices without having to copy the data and transport it
the capacity is limitless
Operating System Roles
- Provides a user interface
- manages security
- provides a platform for utilities/applications
- manages external devices
- managing the processor/scheduling
- managing memory
- provides a platform for networking
- managing hardware
loads the operating system kernel into memory.
Stored in ROM
Where is the waterfall life cycle model used?
Used in manufacturing industry
when the method in the subclass shares the same method as further up in the object tree. the over-ridden method takes precedence and replaces the method further up the object tree
Characteristics of Procedural
instructions, sequences, selections, interaction, procedures and functions
a device that generates a timing signal which changes at a regular frequency. Its used to synchronise communication between the components of the CPU and the rest of the computer system.
Special high speed memory used by a computer. Stores frequently used data and instructions.
A device sends a signal on the control bus to show the CPU it needs attention
character set which displays over a million characters
manages which process to execute next and how much time is allowed to execute a process
What are character sets needed for?
needed so that a document which is made on one computer is still readable on another computer. Computers can have more than one character set installed.
the physical component oft he computer system.
Make sound to send signal
advantages of using an external css file
code only needed to be added to one file but the changes are applied to all the pages that use that css file
program branch reason
occurs due to an if statement, function, procedure call or loop.
primitive data type
a basic data type provided by the programming language as a basic building block
allows you to store multiple items of the same data type under a shared common name
automated process which looks at large sets of data and tries to identify patterns in order to predict something
different types of operating system
Distributed Embedded Multi-tasking Multi-User Real-time
code which takes in data called a key and outputs a hash value which is is used to find a fixed index in a hash table
takes one line of high level source code and converts it directly into machine code then runs it.
this has a one to many relationship and is useful for debugging code however the security is bad and the code is executed slowly
CPU vs GPU
CPUs excel at doing complex instructions on small data sets whereas GPUs excel at simple manipulations to much larger data sets
Client-Server network via the internet, where files are kept on a remote server and accessed virtually
What does the DMBS provide
Security backups index updating enforcement of referential integrity facilities to update and query the database
client side processing
Association LAW (OR)
A∨(B∨C)=(A∨B)∨C= A∨B∨C A OR (B OR C) is the same as (A OR B) OR C is the same as A OR B OR C
USB pens and SD cards
advantages of peer-to-peer
- cheap to set up and maintain
- easy sharing
Algorithm for deletion into a stack:
- Check to see if the stack is empty
- If the stack is empty report an error and stop
- Copy the data item in location pointed to by the stack pointer
- Decrement the stack pointer
a change to a database is either completely performed or not performed at all. A half-completed change MUST NOT be saved back to the database.
any positive or negative whole number e.g. 3, 0, -14
how to normalise a number:
- see how many places the binary point has to move so the number starts 01 or 10
- store this number in the exponent and then new format of the number in the exponen
Fibre Optic Cables
newer, faster and high-capacity
(stages of compilation stage 3)
the syntax tree is converted into object code
Advantages of a client-server network
- Security is better since all files are stored in a central location
- Back ups are done centrally so individual users do not need to back up
- data and resources can be shared
Algorithm for insertion into a queue:
- Check to see is the queue is full
- If the queue is full report an error ad stop
- Insert new data item into location pointed to by the head pointer
- Increment the head pointer and stop
- shut down triggered by user pressing on/off button
- memory parity error (when comparisons don’t match)
- internal clock triggers suspending a running process
why is manageable code important
easy to read, debug and easy to maintain
logic gates in a half adder
XOR (to the sum)
AND (to the carry)
(1) Packages data and passes it on to the transport layer.
Object Orientated languages examples
C++ and Java
The Computer Misuse Act
makes unauthorized access to computer systems illegal:
The intent to commit or facilitate commission of further offences with intent to impair the operating of a computer
when the main memory is almost full sections which are less frequently used are stored on the hard disk to free up RAM space
first normal form
- Eliminate duplicate columns
- Get rid of any groups of repeating data
- Identify the primary key
- Separate out any attributes which are not atomic into separate attributes
Solid-state storage disadvantages
limited lifespan - each section can only be written to a set number of times
software that manages the computer; it manages the hardware, software, security and the user interface
last in first out
what happens when a search engine indexes a page
crawlers traverse the web following links and checking each word in the document. It adds an index entry for the page alongside the words position on the page.
three types of secondary storage
magnetic, optical, solid-state
Method of capturing data (Automated)
barcode readers, scanners, sensors, magnetic ink character recognition, smart card readers
4 types of system software
OS, utility, libraries, translators
joint photographic experts group, losy compressed form of graphics storage
SQL is a language which allows for fast, efficient querying and reporting of vast amounts of data held in a relational database. It is a very high-level language.
Referential Integrity is where table relationships must always be consistent. Any foreign key field must agree with the primary key that is referenced by the foreign key. Thus, any changes to the primary key field must be applied to all foreign keys in another table, or not at all.
based on priority so if one instruction is executing it can be stopped for another instruction to start processing
Dictionary coding is when an index is built where every data item in the file is recorded along with an indexed reference. The final compressed file will just consist of the dictionary index along with the sequence of occurrences needed to recreate the original file.
more bits in the mantissa…
improves the accuracy but reduces the range
reduced instruction set computing. Small Instruction set where each instruction is performed in one clock cycle.
magnetic storage positives
cheap large capacity
if both inputs are true or one input is true the the output is true else the output is false
Advantages of the waterfall model
- Everyone on the project is very clear on their responsibilities at each stage.
- Easy to see if programming is running to schedule
limitations of half adders
- can only add one bit numbers
- only two inputs, the carry from a previous addition can’t be incorperated
data is in its lowest level of detail and cannot be split into separate attributes
is software that annoys users or damages their data. For example, Worms, Viruses, Trojans, Spyware and ransomware.
extensible markup language, text based means of describing data.
types of application software (12)
word processors desktop publishing programs spreadsheets database management Slideshow and presentation Multimedia and video editing photo and graphics manipulation communications, chat and IM social networking email clients web browsers Gaming
real (floating point)
a positive or negative number with a fractional component e.g. 0.002 or -1.98
more likely to have a single instruction to carry out an action, larger instruction sets
works better with more intensive tasks
Data integrity is the state of data being
as intended and accurate
disadvantages of peer-to-peer
- no central backing up
- slower performance
- bad security
CSS identifiers vs classes
and identifier can only be used once on one element but classes can be used on multiple elements
(parallel processing, single instruction multiple data) a single processor carries out an instruction on multiple data
graphics, gaming, AI(machine learning), data analysis
Multi-User Operating System
Allows multiple users to use the system and its resources simultaneously.
Drawbacks of packet switching
- protocols are complex and expensive
- packets may be lost
- not neccessarily secure
a name refer to a particular memory location that is used to store data. The value of the data held in that memory location is not known when the program is written and can change while the program is running
Serialisation ensures that transactions do not overlap in time and therefore cannot interfere with each other or lead to updates being lost
American Standard Code for Information Interchange
three categories of programming languages
A proxy ensures there is no direct physical connection between a single user and a remote source.
disadvantage of server side processing
- can be slow
- pages have to be refreshed often to keep up to date
connects nodes together by broadcasting a signal to all possible destinations. The correct destination will accept the signal
Association LAW (AND)
A∧(B∧C)=(A∧B)∧C= A∧B∧C A AND (B AND C) is the same as (A AND B) AND C is the same as A AND B AND C
difference between paging and segmentation
pages are a fixed size, segments are different sizes
pages are made to fit sections of memory, segments are complete sections of programs
pages are physical divisions, segments are logical divisions
Embedded operating systems
Washing machines, vending machines, car engine systems, traffic lights, pay and display machines
an arrangement where a central node or hub provides a common connection point for all other nodes.
what does security keeping data safe from?
- accidental or deliberate loss
- malicious access
Bus Topology Disadvantages
Main cable is a single point of failure
Limited cable length
Performance degrades with heavy use
What does the width of the address bus determine
the maximum possible memory addresses of the system
Reduces the file size but allows the original data be perfectly reconstructed from the compressed data. Actual data is still removed however the data is encoded in such a way that the original can be recreated.
Less effect at reducing file size than lossy.
drawbacks of open source software
- can be less user friendly/less easy to use
- less support available
- people may exploit failures maliciously before they are fixed
Shortest job first (SJF)
Jobs are sorted in the ready queue according the estimated processor time needed
advantages of client side processing
- Allows for more interactivity by immediately responding to a users’ action
- Removes potentially unnecessary processing from the server
an arrangement where on node is connect to two others to form and ring.
a simple connected graph with no cycles
A field that uniquely identifies each record
Any field which isn’t a primary/composite key which can help make a query more efficient
Disadvantages of rapid application development
- doesn’t scale well
Searching an item in a hash table:
- Feed the key to the hash function
- Go directly to array index (HashValue)
- If the value is equal to the value that you’re searching for then output the value
- Else follow the linked list in sequence until you find the value and output the value
A bi-directional path for moving data and instructions between system components
Graphical processing unit.
used for rendering graphics and processing many parallel streams of data at the same time.
uses of linked lists
- Implementing undo functionality
- Dealing with browser cache
- Helping with operating system job queues
RIPA Grants rights to:
- Demand ISPs provide access to a customer’s surveillance
- Demand ISPs fit equipment to facilitate surveillance
- Demand access be granted to protected information
- Prevent existence of such interception activities being revealed in court
program branch result
the next instruction held in the PC is not carried out
overlapping stages in the fetch-execute cycle.
fetching the next instruction while the first instruction is being decoded
example of input AND output device
touch screen or games controllers
Embedded Operating Systems
a computer system that forms part of a device such as a washing machine or car
- instructions and data are stored in separate memory units
- instructions and data are each served by their own buses
- allows for pipelining
A unique identifier made from different fields
positives of databases?
- provide security
- provide automatic backup
- enforce data integrity rules
- control data redundancy
- provide users with controlled access to data they need
the original class and its code
combine rows from multiple rows
What does a bitwise right shift do?
divides the number by 2.
If the result of a binary addition is greater than 255, an overflow error occurs, where the most significant bit requires a ninth bit (Put it in brackets)
negatives of multiple cores
complicated circuitry (more expensive) doesn't always improve performance
by changing the position of the binary point you can…
increase the size of the number
increase the accuracy of the number
multiple instruction multiple data, multiple instructions are carried out on multiple data using multiple cores
Local Area Network (LAN):
method of connecting computers together in a small geographical area. All the hardware and infrastructure is owned by the business/ organisation that uses it.
Benefits of Open source software
- usually free
- users are free to amend the source code and tailor the program to their needs
- not constrained by commercial considerations
- many people are continuously finding and fixing bugs
the process of creating an object from a class template
Uses of Multi-tasking operating systems
desktops and smart phones
Entity Relationship Modelling
when the relationships between tables are shown in abstracted view.
more complex circuitry/hardware Single machine instruction takes multiple machine cycles to carry out greater energy consumtion can't support pipelining more silicon require to make physically larger in size
How does Java use virtual machine?
the virtual machine execute intermediate code (Java Byte code)
Half adder outputs/inputs
inputs: the two bits to be added
outputs: the result and the carry
Algorithm for deletion/reading from a queue:
- Check to see if the queue is empty
- If the queue is empty report an error and stop
- Copy data item in location pointed to by the tail pointer.
- Increment tail pointer and stop
Writing an alert box
Search engine indexing
Uses web crawlers and relies of databases of indexes, and uses those indexes to find more databases forming links
divides the page into segments allowing for improved styling
any device which allows you to get information from the outside world into a computer system so that it can be stored in a digital form
utility programs examples
- Disk defragmenter
- Automatic backup
- Automatic updating
- Virus checker
- Compression software
- Buffer almost empty
- Signals the completions of data transfer between devices
First come first serve (FCFS)
the processes are executed in the order they arrived
if all the processes take along time all the others must wait
how does the PC know where to return to in the previously executing program after services an interrupt
by putting instructions on a stack
how to use a form tag
chosenElement = document.getElementById(“example”);
chosenElement.innerHTML = “Hello World”;
Benefits of packet switching
- efficient use of the network
- can be rerouted to avoid problems in the network
- data is transmitted immediately
Used to process data on clients computer which allows erroneous data validation on client side which is quicker and relieving on a server side.
Organising the attributes and relations of a relational database to minimise redundancy
a program that blocks unauthorised access onto a network by inspecting packets to find the port they are attempting to access through.
If the port is blocked then the packet is rejected.
elemental sequential logic circuit that can store one bit and flip between two states
Server side processing
data is processed on server side as they can process bigger amounts and take the strain off clients
A method of transforming data into an unintelligible way so that it cannot be read by unauthorised individuals.
Advantages of rapid application development
- flexible to changes
- can reduce risk
Input/ Output interrupts
buffer nearly empty
signal the completion of data transfer to/from a device
any program that converts source code into machine code. e.g. interpreters, compilers and assemblers
Disadvantages of Networks
The user can become dependent on the network
If the network stops operating then it may not be possible to access various resources
Efficiency of a network can be very dependent on a network manager
It is difficult to make a network of computer secure for hackers and outside threats
As traffic increases on a network the performance can degrade
branch if zero instruction
more machine code (not as many instructions)
lower clock speed, not good with complicated tasks
advantages of server side processing
- doesn’t require plugins or browser scripting technology
- more secure
- reduces loading time
third normal form
- Check the data is already in 2NF
2. Check there are no non-key-dependencies
programs which attempt to consolidate the spilt files and free space. therefore reading and writing files becomes more efficient.
A Trojan is software that misleads the user of its true intent. Often, they serve to open up back doors in your computer.
the principle of dividing a complex system into separate slices of functionality
4 types of application software
off the shelf, custom written, proprietary and open source
an un-ordered data structure which is accessed through an attribute. It can store many different data types.
capacity of optical
700MB - 50GB
branch if zero or positive instruction
Memory Address register (MAR)
stores the address of instructions and data that need to be fetched from or sent to memory
Advantages of using byte code interpreters
- Achieve platform independence
- Acts as an extra security layer between program and computer
Bus topology advantages
Inexpensive to set up
Devices can easily be added
Good for small networks
only good if you can predict subsequent instructions. If the wrong instruction is fetched it has to be thrown away wasting time.
create a new table SQL
CREATE TABLE tblName
Why is paging not efficient
it does not take into account what the instructions in each page are doing
What is a mask?
A mask allows you to isolate, extract, toggle and set bit values in a sequence of bits.
Clock speed Unit
Hertz (usually gigahertz)
A port is used to alert a specific application to deal with data sent to a computer. These are used by protocols to specify what data is being sent.
the communication channels between the CPU and the memory and other components.
multimedia platform for creating and displaying graphics (replaced by HTML5)
Inserting items into a binary search tree:
look at each node starting at the root. If the new value is less than the value at the node, move left otherwise move right. Repeat this for each node arrived at until there is no node. Insert a new node at this point and enter the data.
What does ASCII stand for
American Standard Code for Information Interchange
Negatives of Symmetric encryption
There is a security risk as the key may be intercepted or the process of creating the key may be duplicated meaning the data can be decrypted by a third party.
Non pre-emptive algorithms
- First come first serve
- shortest job first
Benefits of asymmetric
- no movement of keys, more secure
- can be used for digital signatures
data storage instruction
binary search tree
dynamic data structure which can grow and shrink during a programs execution. It allows for efficient sorting, searching and retrieval of data.
a binary tree can have 0, 1, or 2 children only.
Optical storage disadvantages
slow access speed
the surface of the disk degrades over time
scratches can corrupt data
What does an OS provide?
- User interface
- Memory Management
- Interrupt handling
- Processor scheduling
writing to a file
myFile = openWrite(“sample.txt”)
Why Do RISC processors result in increased battery life
- smaller instruction set
- fewer transistors/ less complex circuitry
- less power required
Negatives of increasing clock speed
more heat generated meaning computers must be cooled (either with heat sync/fan or water/oil cooling)
Triggered regularly by a timer, to indicate that it is the turn of the next process to have processor time- this allows for multi tasking
if both inputs are true the output is true else the output is false
a subroutine associated with an object
Wide Area Network (WAN:
a method of connecting remote computers or networks. Typically made up of smaller LANs which have been connected together.
non-volatile read only memory embedded into the motherboard of a computer and used to hold important instructions the computer needs for starting up
examples of system software
Operating system, Utility Program, Library Program, Translators.
why can assembly code for one processor not work for another processor
each type of processor has its own unique instruction set
Device drivers are…
hardware dependent and OS specific
Databases are structured, persistent collections of data.
Uses of RISC
used in most smart phones and tablets based around an ARM processor
boot up process of a computer
- POST is run
- clears anything in the registers
- loads the address of the first instruction of the boot program into the PC
- the boot program checks for start-up instructions on the BIOS
- The OS kernel is loaded
What is bitwise manipulation useful for?
- Compression Algorithms
- networks (protocols. routing packets)
- multiplication and division
Wireless Access Point
use wireless to connect a node to a WiFi network avoiding the need for lots of physical caballing
fixed point binary
positive of the binary point is fixed on the number line
- Visit the root
- Traverse the left sub-tree
- Traverse the right-sub-tree
Parallel processing/concurrent processing
multiple processors working at the same time
- Methodology which stages of software are not completed in a linear sequence
- Throughout the process feedback is obtained which changes the software
- It is a smaller version of spiral
Advantages of the spiral model
- good from projects with high levels of risk
- suitable for large scale problems
benefits of symmetric
- encrypted very quickly
- simple and easy
a processor designed for specific purposes which can carry out specialised tasks more quickly than a regular microprocessor. execute concurrently with the main CPU
width CSS property
advantage of normalisation
it stores the most accurate version of that number.
while loop pesudocode
(cloud storage) when data is stored over the internet on cloud storage instead of on local storage device
Von neumann architechture
- instructions and data share the same memory space
- instructions and data served by the same system bus
- instructions and data are stored in the same format
- single CU and ALU
Procedural programming languages
programming languages where the user gives step by step instructions of what to do
automated decision making
computers make decisions and take actions based on sets of pre-defined rules and parameters without human involvement
programs which attempt to reduce the amount of physical space that files take up when they’re stored
collective term for address, data and control bus
single table database. It is inefficient as it is difficult to query and leads to data redundancy which can cause errors.
Shortest remaining time (SRT)
The ready queue is sorted on the estimated time to complete the process. If the remaining time of a running process is longer than a new process the new process will be moved to the running state
Bitwise shifts can be used …
to change numbers quickly
hash total is encrypted using the users private key. If the receiver can decryptit using the senders public key they know that the message is authentic
Uses of Multi-user operating systems
schools and offices
the deliberate supression of material, either in the form of what can be published or what can be accessed
Benefits of high level code (over assembly)
- optimisers may make code more efficient
- intuitive and easier to write
- can be recompiled for different architechtures
- less code is written (shorter programs)
Internal css vs external css
internal is within the document external is linked to html code
- Traverse left sub-tree
- Visit the root
- Traverse the right sub-tree
(stages of compilation stage 2)
the syntax is checked against the rules and an abstract syntax tree is created
if any code breaks the syntax rules an error is generated
Condition between two values SQL
WHERE x BETWEEN a AND B
The Regulation of Investigatory Powers Act
gives certain bodies the right to monitor communications and internal activity. It was made due to modern threats from criminals and terrorist organizations.
flip flop logic gates
Two NAND gates with two inputs. The result of of each is the second input for the other.
Benefits of assembly code (over high level)
- efficient as the code is more specifc
- direct control of hardware
- good if no compilers/interpreters installed
- good if limited memory
integer division (rounds down)
Round robin (RR)
each process is allocated a specific amount of time known as a time slice or quantum. if a process is not complete at the end of the time slice it returns to the back of the queue, so the next process can have its turn.
- Round Robin
- Shortest Remaining Time
- Multi-level feedback queue
Multi-level feedback queue
uses multiple queues based of the priority of the process.
Uses of Hashing
- generating disk address
- storing and checking passwords
- Traverse the left sub-tree
- Traverse the right sub-tree
- Visit the root
full image tag
A document listing all the functionality the system should have
external storage examples
DVDs, CDs, Blue-ray, USB pens, SD card, Portable solid state drive, Mass storage tape, cloud storage.
Meta tags, keywords, descriptions
Search engines look for this to find the content that matches your search
Absorbtion Law AND
A∨(A∧B) = A X OR (X AND Y) is the same as X
do a set of statements again and again (looping)
delete rows of a table
Bottleneck data bus
A wider bus can transmit larger values/ more bits per instruction
the protection of attributes and methods of an object so that they can’t be accessed or altered by other objects. (keyword - private)
Where is RAD used?
good for when the project requirements aren’t completely clear from the outset
Multi-user operating system
more than one user is able to use the computer at one time. The operating system manages user preferences. Tis is often used for servers.
the new class which inherited from the superclass
condition controlled time
repeat a set number of statements until a condition is met
the actual number you want to store
Application Programming Interface (API)
a set of tools that can be used for building software applications.
Where is extreme programming used?
good for when the requirements change
Algorithm for insertion into a stack
- Check to see if the stack is full
- If the stack is full report error and stop
- Increment the stack pointer
- Insert new data item into location pointed to by the stack pointer and stop
stores the result of calculations made by the ALU
A program that manages the amount of time different processes have in the CPU
Control Unit is a register in the CPU that controls and co-ordinates the activity of the CPU. Control signals are sent along the control bus between the control unit and the other components of the computer.
The individual parts of the list <ol> <li> </li><li> </li><li> </li> </ol>
example uses of flip flops
- in registers
- static RAM
distributed operating systems
combing the processing power of multiple computers for a single task across a network. The OS controls and co-ordinates the computers, presenting it to the user as if it were a single system.
- designed to try and manage risk. made of four stages:
1. determine objectives
2. Identify and resolve risks
3. development and testing
4. plan next iteration
Antivirus utility software
programs which help to detect and remove malicious programs which are often designed to harm the computer.
read only memory
when memory is split up however the logical divisions of a program are kept together, rather than having fixed page sizes
CSV (Comma Separated Value)
A text file/format with values separated by
programs which allow for manual or automatic backing up of files onto another disk, on the existing computer system, to a removable device such as DVDs or CDs, to a network file server or to a cloud based storage system online
order of main HTML tags
fast read-write volatile memory that stores the data and programs the computer is currently using e.g. OS, Programs currently in use, data that the programs are accessing
Memory write signal
causes data on the data bus to be written into the addressed location in RAM
Purpose of Compression
- Reduce download times
- Reduce requirements on file storage
- Make best use of bandwidth
portable document format, to display documents exactly as intened
d page rank
The damping factor to prevent the rest of the equation from having too much influence
relationship between the DNS server and IP addresses
a registered domain name is held on the DNS server. The corresponding IP address to a searched domain name is loaded on the users computer.
A Worm is a standalone program that does not require a user to run it in order for it to spread.
Disadvantages of the waterfall model
- The absence of user feedback
- not suitable for large projects
- Requirements must be very well understood
positives of multiple cores
may speed up processing
Arithmetic Logic Unit
Carries out calculations and logic (Comparisons of binary)
- Memory read
- memory write
- bus request
- clock signal
by default how are parameters passed?
Any true/ false data types which often represent logical situations
closed source software
software which is supplied pre-compiled. The source code is not available and often copyrighted, also known as proprietary software
e.g. microsoft word
graphics interchange format, lossless compressed image file format
(2) Makes and breaks connections with routers
Registers are small storage locations used to hold data temporarily. They have high read and write speeds.
Deleting an item in a hash table:
- Feed in key to hash function
- Go directly to array index (HashValue)
- If the value is equal to the value you’re searching for then mark as empty
- Else follow the linked list in sequence until you find the value then mark as empty and update the free pointer in the linked list.
the data remains for as long as its required
Transaction processing is any information processing which is divided into individual, indivisible operations each operation must secede or fail as a complete unit.
Order Queried data SQL
Where is the spiral model used?
Used in large scale projects
metropolitan area network
need for secondary storage
Can retain contents when the computer’s power is turned off. This includes the Hard drive, optical media and solid state storage.
reading from a file
myFile = openRead(“sample.txt”)
x = myFile.readLine()
Move/blink to send signal
Instance of a class
structure and data cannot be changed at runtime
multiple tables linked together
data bus width
same as the computers word size
used to quickly access and locate data in a table
When is Bitwise ANDing useful?
useful for TCP/IP and routing
nodes with no sub-nodes
leaf-nodes or terminal nodes
Check if an attribute is similar to a given value SQL
The contents of the CIR are sent to the CU and divided. The Opcode tells you the instruction to be carried out and the operand stores the address of any data which might be needed, the operand is sent to the MAR and the data is fetched from memory and stored in the MDR
Loaders (dynamic linking)
compiled versions of libraries are stored by the computer and the operating system links the code directly into the program when it is needed reducing the size of programs. Loaders are needed to include or load the libraries into memory ready for use.
A composite key is a combination of two or more columns in a table that can be used to uniquely identify a row.
Advantages to Peer-to-peer networking
- Enables users to share resources
- not difficult to maintain
single equals, sets the value on the right equal to the value on the left
generates and detects interrupts
signified by the key word new, initiated instantiation
(stages of compilation stage 1)
white space is removed
remaining code is turned into tokens
a symbol table is created (including variables, data types and scope)
a transaction must not be able to be interrupted by anther transaction. The transaction must occur in isolation so that other users or processes cannot have access to the data concerned.
a low level language represented by mnenomics which represents the machine code.
more bits in the exponent…
improves the range but reduces accuracy
name used to refer to a fixed value. The value is set when the code is written and cannot change while the program is running
very simple hardware/circuitry less silicon needed
each instruction is a single machine cycle therefore pipelining can be used to improve performance
lower energy consumption (can go into sleep mode)
collision (hash table)
when the same hash value is given by two different keys
advantages of Client-Server
- User IDs, passwords and access levels centrally controlled
- Backup is centralised and usually automated
- No access to other users’ files
breadth first traversing
It starts at the root node, and visits all of the neighbor nodes at the present depth prior to moving on to the nodes at the next depth level.
negative of increasing cache size
Multitasking operating system
can run multiple programs simultaneously
defines a form that is used to collect user input
a sub-routine that make take one or more parameters and ALWAYS returns a value
Full adder inputs/outputs
inputs: the two bits to add, the previous carry bit
outputs: the result, the carry
any combination of letters, symbols, numbers, characters or control characters e.g. Hello, £4.56
magnetic storage examples
magnetic tape, floppy disks hard disk drives