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year 10 exam revision computer science - Coggle Diagram
year 10 exam revision
computer science
control unit coordinates the actions of the computer. it sends out controls signals to other party's of the CPU and to other components of the computer
control signals make everything happen inside a CPU and computer
an important element is the decoder this works out what program instructions mean it then sends control signals to other components to carry out the required
von neumann architecture
in 1945 neumann designed a stored program coimputer where both the program and the memory were stored in memory.
the components are: a processing unit or CPU/ a program counter/ memory to store data and instructions/ input output mechanisms
the Arithmetic logic unit performs arithmetic logical operations it carries out activities such as addition, subtraction, multiplication, division, comparisons between to different numbers
secondary storage
data can be stored on secondary storage devices there are three main types of storage device: magnetic discs, optical discs and solid-state [flash] memory
data and programs are stored operantly on secondary storage devices but on the CPU cannot access them directly and so they must be transferred to the main memory
magnetic storage is used in hard discs and digital tape drives which are often used for backing up large computer systems, magnetic
discs consist of stacks of non-removable discs coated with magnetic materials data is encoded as opposing magnetic polarities on the surface of the disc electromagnets in the read write heads read and write the data the cost of magnetic hardware is low hard disc drives in budget laptop have capacities of at least 1 terabyte
optical storage includes compact discs that store 700MB, digital versatile discs that store 4.7 GB Blue ray discs that store up; to 50 GB optical discs use a laser to read and write data. the data is encoded as a a series of pits in a spiral track running from the inside to the outside of the discs
solid state memory is made of flash memory flash memory is non-volatile storage that can be electrically erased and reprogrammed. Flash memory uses arrays of transistors transistors can operate in two states 0, 1 and are switched from on e too the other using electrical signals. data is encoded as sets of binary digits 8 GB of solid-state storage require 32 billion transistors
client- server network
in client server networks there are two types of computer file
servers
= computers which control access and mange the network and
clients
= computers on which the users work
users log in to the servers to access program and data stored on them
servers are responsible for network security by allocating login names and passwords no users
all files are held on the servers and can be backed up centrally
peer-to-peer network
in peer-to-peer networks there is only one type of computer
there is no server to manage the network all the computers are connected equally.
they are all equal and can communicate with each other directly without having to go through a server
each client can act as a server other clients can share programs data and printers security is distributed each user can grant rights to other to allocate passwords data in stored on each client and not centrally each user is responsible for backing if each client
bandwidth ----- Bandwidth is the amount of data that can be transmitted per second. bandwidth is measured in bits per second
network topologies
star topology
each computer is connected individually with an centrals point or node which can be a file server hub/s witch
advantages of star topology
data is only directly to the intended computer directly network traffic is kept to a minimum if one link fails all the other devices will continue to operate it is easy to add new devices without disrupting the network
disadvantages of a star topology:
if the central point fails then is will the entire network requires a lot a of cable as each computer is connected individually to the central component