Topic 4 Computers
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List a range of input devices
Mouse Keyboard Microphone Camera
List a range of output devices
Monitor Printer Speakers Vibration pack
Describe the relationships in the Input, Process, Output model.
All output is the result of inputs which have been processed, ie. Input -> Process -> Output
Name all of the components of the CPU (Central Processing Unit)
Control Unit Decoder Clock Arithmetic Logic Unit Cache Buses Registers
If a CPU has a clock speed of 3GHz, what does this actually mean?
It can carry out 3 billion processing cycles per second.
What significant factors affect the performance of a CPU?
Clock speed Cache Size Number of cores Size and type of RAM Hard drive speed
Describe Von Neumann architecture.
Programs and data stored in the same memory (RAM). Components are: • CPU • Program Counter • Memory • Input / Output
Describe the role of the control unit in a CPU.
• Coordinates the actions of the computer. • Sends control signals to other parts of the CPU. • Contains the decoder which works out what the instructions mean
Describe the role of the arithmetic logic unit (ALU) in a CPU.
• Performs arithmetic and logical operations • Addition, subtraction,multiplication, division • Comparisons between two different numbers (eg , <= etc)
Name the four registers used in the Fetch-Decode-Execute cycle
• Program Counter (PC) • Memory Data Register (MDR) • Memory Address Register (MAR) • Accumulator
State what is performed at each stage of the Fetch-Decode-Execute cycle.
Fetch: The next instruction to be executed is transferred from RAM into the CPU. Decode: The control unit (decoder) interprets the instruction. Execute: The control unit carries out the instruction. If calculations are needed, these are performed by the ALU.
Describe RAM
RAM - Random Access Memory • Stores data and instructions while a program is running. -Main memory of the computer. • Volatile - data is lost if power turned off
Describe ROM
ROM - Read Only Memory • Stores instructions to initialise hardware and load operating system • Data can only be read from ROM, not written to it • Non-volatile, data retained when power is off
Describe cache memory
• Very fast memory • Stores recently or frequently used instructions to speed up processing • Instructions don’t have to be fetched from RAM as often • Too expensive to use as RAM
Name the three main types of secondary storage device
• Magnetic discs • Optical discs • Solid-state (flash memory)
Why is secondary storage needed?
• Data/programs are stored permanently on secondary storage but cannot be accessed directly by the CPU. • They need to be loaded into RAM first. • RAM is volatile therefore cannot store permanently.
Describe the features of magnetic storage
• Includes hard disc drives with large capacities • Consists of stacks of non-removable discs coated with magnetic materials • Discs spin and a read/write head moves across them • Data is encoded as opposing magnetic polarities on the surface • Using electromagnets in the read/write head
Describe the features of optical storage
• Includes CDs/DVDs/BluRay • CDs store up to 700MB • DVDs store up to 4.7GB • BluRay discs store up to 50GB • Single spiral track on the disc • Data etched into the track as pits • Read by a laser
Describe the features of solid-state memory
• No moving parts (unlike magnetic/optical) • Made of NAND flash memory • Non-volatile • Consists of floating gate transistors • Electricity is used to change the state of the transistors (0/1)
Give three examples of the use of solid-state memory
• SSDs (solid state drives in computers) • SD cards for use in portable devices like phones/cameras etc • USB flash drives (memory sticks)
What is meant by cloud storage?
• Off site storage - Made available to user over a network (usually the internet)
State some advantages of cloud storage.
• Stored off-site so secure from fire/damage on-site • Can be accessed from anywhere with an internet connection • No need to buy expensive storage devices • Allows collaboration around the world • Data can be synced between a range devices (PC/Phone/Tablet etc)
State some disadvantages of cloud storage.
• An internet connection is needed to access it • Download/upload speeds affected by the internet connection • Cloud company could be targets for hackers • Less control over your data as held by another company • Storing confidential data online may be in breach of legislation (DPA / GDPR)
What is meant by an embedded system?
A computer system built into another device in order to control it. Eg, Washing machine, microwave, digital camera