unit 4 - computer systems Flashcards
two types of main memory
RAM (random access memory) and ROM (read only memory)
RAM
- doesn’t automatically save (volatile)
- much faster to access than a hard drive
- the name random access memory comes from the ability of the CPU to access any part of the memory in the same amount of time
ROM
- used to store data when a computer isn’t on
- data is read from ROM, but cannot be written to it
- it is non-volatile as the data isn’t lost if the power is off
what does RAM usually store?
- the operating system (or part currently in use)
- the software currently in use
- the data which the software is using
what does ROM usually store?
- the initial program that is run when the computer is turned on
- it tells the computer where it will find the operating system on the hard drive
- it also stores the Basic Input/Output System (BIOS)
storage vs memory
- memory keeps the things you’re currently using but is volatile
- storage isn’t volatile and will store your work in the computer
BIOS
controls basic technical configuration of the computer such as the processor speed and system time
differences between RAM and ROM
- RAM is bigger (4GB-32GB) than ROM (4MB-8MB)
- RAM runs programs and operating systems whilst ROM stores BIOS and the initial computer program
- RAM is volatile whilst ROM is not
- you can read on both but can only write on RAM
memory speed
- the speed that data can be accessed changes through the different components in a computer
access speed (in order)
processor > cache > RAM/ROM > virtual memory
explain why increasing the amount of RAM will improve the performance of a PC
- hard drives have a slow access speed compared to RAM.
- RAM is far faster – so for programs and data currently being used this
makes the computer perform better
secondary storage devices
Blu-ray drive
DVD drive
CD drive
Tape drive
Removable flash media / USB stick /SD card
secondary storage
storage that isn’t accessible by your CPU
- non-volatile
- can be internal and external to the computer
uses of secondary storage
- programs stored on hard drives
- blu-ray/dvd/cd - stores films
- memory sticks used to transport data from place to place
- SD cards - additional storage on cameras and phones
- magnetic tape - stores backups
stores programs + data
data rate
the rate at which data can be accessed
basic features of magnetic disks
- contains concentric circles called tracks
- each track is divided into sectors
- disk heads mounted on mechanical arms read and write the data
features of a hard disk: magnetic storage
- a very large storage capacity, up to 6TB or more
- a very cheap form of storage compared to solid state drive
- portable hard disks can be connected to a computer via a USB port - they are used for backing up or transporting data
advantages of magnetic storage
cheap, large storage capacities, relatively fast write speed
disadvantages of magnetic storage
lots of mechanical parts, durability an issue, sealed unit due to disk head and platter precision and not very portable
uses and capacities of magnetic storage
- personal computers - stores large quantities of data
- 500GB - 12TB
basic features of optical storage
- data is stored as pits and lands burnt or pressed into a spiral track circulating outwards from the centre
- a laser beam reads and writes the data using light
- stored as either pits or lands
- from this signal, 0s and 1s can be derived
advantages of optical storage
- cheap, very easily portable, takes up little space physically
disadvantages of optical storage
- less storage capacity compared to other types
- easily damaged / scratched, requires a CD reader
- slow write speeds
uses and capacities of optical storage
- songs, videos and other multi-media storage, backup and archiving of data
CD-ROM – up to 720 MB
DVD – up to 8.4 GB
Blu-Ray – up to 50 GB
why does blu-ray have better quality than a cd
- it has smaller pits and lands
solid state storage
- data is recorded onto solid memory chips without any moving parts
basic features of solid state storage
- use non-volatile flash memory to store information
- very fast read/write speeds as it doesn’t need to wait for a disk to spin
to the correct location and an arm to move - no mechanical or moving parts meaning these disks are very durable
advantages of SSD
- highly durable, no moving parts, very fast read/write speeds, no noisy fan or drive arm, faster start up times
disadvantages of SSD
- more expensive than magnetic hard disks, similar storage capacity as magnetic disks
uses and capacities of SSD
- higher end computers
- laptops
- smartphones and tablets
100GB - 16TB
capacity
how much data it can store
speed
how fast the data can be read or written
portability
how easy it is to transport
durability
how easily damaged it is
reliability
how likely it is to lose the data
cloud storage
saving data in an offsite storage data system maintained by a third party
examples of cloud storage
- dropbox
- google drive
- amazon web services
how does cloud storage work
- data is saved to servers at a remote location and anywhere in the world
- data is accessed via the internet
- either uses magnetic storage or solid state/flash storage
advantages of cloud storage
- easily accessible
- you can efficiently back data up because all your devices are synced
- because copies of your data are stored in different locations, if the server crashes the data won’t be lost. it can still be accessed from a different server
- doesn’t require the user to have storage on their own computer
disadvantages of cloud storage
- requires internet to access it
- makes it more susceptible to hacking
- you have to subscribe to get more storage
- uploading and downloading data takes time and is dependent on their internet connection
input/output devices
devices that allow you to input data and receive data
primary storage
memory in which computers can store data or instructions that are currently in use
embedded systems
a computer system built into another device to support its operation.
general purpose systems
capable of performing many tasks eg. smartphones, macs, pc
what do 1 and 0 represent?
TRUE and FALSE
truth table
- a way of evaluating a boolean expression
- shows every possible combination of inputs and the outputs
boolean function: AND
if both inputs are TRUE then the output is TRUE
boolean function: OR
only one of the outputs has to be TRUE for the output to be TRUE
boolean function: NOT
inverts the input
- if the input is TRUE then the output is FALSE
- if the input is FALSE then the output is TRUE
hardware
the physical components that make up a computer
examples of hardware
processors, memory, storage, input/output devices
software
the programs which run on a computer
examples of software
operating systems, utility programs, apps
logic symbols:
AND: .
OR: +
NOT -
XOR: + in a circle
boolean function: XOR
if just one input is TRUE than the output is TRUE but if both inputs are TRUE then the output is FALSE
operating system
system software that acts as an interface between the user and the hardware, managing all hardware and all other software
- software must be launched from the operating system
what is managed by the OS?
processors, memory, i/o devices, apps, security
os managing processors
- decides which processes will be carried out by which processor
- if multiple processes are running, which one the processor should handle next
- how long of a time slice each process should be given
os managing memory
- loads programs and data backup store to main memory
translators
special software that convert source code into executable binary
compilers
- translate the whole program in one go
- will provide a list of errors once it has attempted the compilation process, which makes debugging easier
- compiled languages: C, C++, visual basic
pros of compilers
- produce an executable program; no need to repeat the process more than once per version of software
- compilers hide the source code from the end user; helps to protect the developers’ intellectual property
cons of compilation
- the process can be very slow in development if many small changes need to be made
interpreters
- converts high-level languages to executable machine code
- takes place one line at a time (rather than in one go)
- interpreted languages: python, javascript
pros of interpreters
- they will stop as soon as they encounter an error, useful for debugging
- they are ‘portable’ can be run on many different types of CPU
- quicker to get started which is good for making small changes
cons of interpreters
- interpreted programs are slower than compiled ones because you have to translate every line (each time the software is run)
- doesn’t have a compiled program file so the process must be repeated each time the program is run
assembly
low-level programming language
each instruction directly corresponds to a binary sequence, and the assembler replaces the command with the relevant binary
pros of assemblers
- assembly has exact control of the hardware meaning that the code if efficient and takes up little memory which is quick to execute
- can be used on low spec machines
cons of assemblers
- assembly is difficult to use and requires technical knowledge
types of translators
- compilers
- interpreters
- assemblers
transistors in the CPU
- they are arranged into circuits to perform operations such as calculations when electricity is passed through them
- modern CPUs contain over 3 billion transistors which perform calculations by the second
transistors
- act as electrically- controlled switches
- 1 = presence of electricity and 0 = absence of electricity
logic gates
multiple transistors can be arranged together to make logic gates (complex switches) that only allow electricity flow if some or all of the transistors are “on”
logic circuits
a combination of logic gates
application software
- helps a user of a computer system to complete a given task
examples of application software
- word processors
- web browsers
- powerpoint
system software
- controls the hardware of the computer and provides an environment for the apps to run
device drivers
- one type of system software
- small programs which tell the operating system how to use a piece of hardware
utility software
- type of system software
- performs maintenance tasks to make sure the operations of the system
types of system software
- operating system
- device drivers
- utility software
four main types of utility software
- compression
- defragmentation
- encryption
- backup
compression
- applying an algorithm to reduce the space needed to represent a file or its content
encryption
- designed to prevent unauthorised access to files by applying an algorithm to “scramble” data
defragmentation
- improving the hard disk performance by applying an algorithm to reorganise data
backup
- making copies of data that can be restored in the event of data loss
purpose of the operating system
a piece of system software the hardware within a computer
API
- application programming interface - a set of code libraries that software developers can use to write applications for that operating system
graphical user interface
- has the drag and drop feature so that you can easily exchange information between software
eg. windows XP, apples OSX
purpose of memory manager
- controls the allocation of RAM to each running process
- if it fails to do so, the computer will fail and crash
purpose of process manager
- allow users to run multiple programs at once
- a CPU can only execute one process at a time so it must switch between processes so quicky that it seems that they are running simultaneously
