Paper 2 Flashcards
chapters 5 - 12
Intermediate code
code which is not directly executable, it will be interpreted/run by a virtual machine and can be run on different platforms
advantages of an interpreter
- used for testing - don’t have to run the entire code
- translated line-by-line and therefore can run with errors
- the program can be executed immediately and doesn’t have to wait to be compiled
- when executed, the interpreter and source code are always required.
advantages of a compiler
- more secure as you can’t access the source code
- translated all at once into object code
- once compiled, it can run at any time
- when executed, the compiler isn’t needed
compression
the process of reducing the number of bits required to represent data
bitmap
pixels of an image are mapped to positions in memory that store binary codes which represent the colour of each pixel
pixel
the smallest possible addressable area (smallest solid block) of colour in an image
cartesian product
combining the elements of 2 or more sets to create a set of ordered pairs
subset
a set where the elements of one set are entirely contained within another
proper subset
where one set is entirely contained within another
real numbers
any number that can represent a distance along a line. this includes all rational numbers and all irrational numbers
limitations of caesar cipher
- computationally insecure
- letter frequency analysis can be used to determine the shift
- there are only 25 possible shifts
- key exchange problem - key needs to be wecurely sent to the recipient
encryption
the process of converting plaintext into cyphertext which cannot be understood without the key to decrypt it
why was unicode introduced?
- to share more characters across more languages
- can represent a wider range of characters
- however, it uses more bits for each other
why is hexadecimal used?
- easier for humans to read and understand
- more compact when displayed
advantages of thin-clients
- easy and cheaper to set up new clients
- hardware and software updates only need to occur on the server
- easier for the network manager to control clients
- greater security due to reduces access rights for clients
thick-client system
resources are distributed between the server and the client computers
thin-client system
one computer has the majority of the resources and it distributes these resources to other computers
features of a public IP
- globally unique
- visible to all devices on the internet
- routable
- direct connect to internet
features of a private IP
- locally unique
- not visible to devices outside the LAN
- non- routable
- connects to internet through a gateway
differences between JSON & XML
JSON is easier to read, more compact, and quicker to parse than XML
concurrent access
two users try to update the same record at the same time
serialisation
ensures only one transaction at a time is executed
primary key
an attribute which uniquely identifies a record in a table
composite key
a collection of attributes which uniquely identifies a record in a table
foreign key
an attribute in a table which corresponds to the primary key field of a different table
what are check digits and how are they calculated
- added to the end of binary data to check (but not correct) the date is accurate
- it is calculated by applying a function to the value, until the result is a single number
e.g. 12975 -> 1+2+9+7+5 = 24
2+4 = 8//
MIDI (musical information digital interface)
a way of representing the sounds made by an instrument
clock
device that generates the signal used to synchronise the components of a computer
software
programs to be executed by hardware
cardinality
the number of elements in a set
utility programs
performing specific tasks to assist the computer
library programs
compiled routines which other programs can use
object code
compiled code which can be run as an executable file
processor
executes programs and supervises the other parts of the system
RAM
holds instructions and data for programs currently running. the contents of RAM are lost when the computer is turned off
registers
fast memory location inside the processor
factors affecting processor performance
- increasing the word length
- increasing the bus width
- multi-core
- cache memory
- doubling clock speed, doubles processor performance
cache memory
temporary memory that’s separate from main memory and can be accessed much more quickly, so programs can run faster.
Increasing cache memory increases the speed at which programs can accessed
logical bus topology
data packets are broadcast to all devices, but only the intended recipient processed the information
packet switching
a method for transmitting packets of data on a network (usually the internet)
world wide web
a service provided on the internet for viewing hypertext documents
when to use peer-to-peer LAN’s
- there are a small number of devices
- the users are all located in the same area
- security is not an issue between peers
laser printers
a rotating drum inside the printer is coated in a chemical which holds an electrical charge. the laser is reflected onto the drum via a rotating mirror. the laser neutralises the electric charge on the drum where the image should be black. the toner is given a positive charge and the drum picks up the toner. the drum is rolled onto paper, the toner is transferred to the paper. the paper is heated to fuse the toner to the paper.
digital still camera
the shutter opens and lets light in through the lens. the light is focused onto a sensor, usually a CCD. the sensors are made up of millions of transistors, each stores the data for a pixel. as the light hits the sensor, the amount of charge is recorded for each pixel as binary. camera uses 3 sensors per pixel (R,G,B)
optical disk
data is encoded as a series of bumps or pits within the track. a protective layer is then put over the surface to prevent corruption. pattern of pits represent binary data.
when the CD is read, pits and lands are read by a laser which then interprets an electrical signal. electrical signals are then converted to binary
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