3.4 Computer Systems Flashcards
Definitions of hardware and software:
What is the relationship between them?
Hardware: physical stuff that make up the computer system
(CPU, motherboard, monitor, printer)
Software: programs a computer system runs
(Application software, system software)
Work together to process data/complete tasks
Name the 3 logic gates and their shapes:
NOT = triangle AND = semi-circle OR = rocket
What is system software?
Vs
What is application software?
System Software: software designed to run and maintain a computer system
(OS = Operating System, Utility software)
Application software: programs that help the user perform specific tasks
(Word processors, web browsers, games)
Main functions of Operating systems (OS):
manages hardware and runs software
Main functions:
- communicate with input/output devices via device drivers
- provide platform for applications to run on & a user interface
- control memory management & allocation
- organise CPU & its processing tasks
- deal with file management & disk management
- manage system security & user accounts
Explain the Von Neumann Architecture:
What does each part do?
- describes a system where CPU runs programs stored in memory
- programs consist of instructions/data stored in memory addresses
- CU controls flow of data & keeps track of memory address of instruction for next cycle
- memory holds program instructions/data
- ALU gets data from CU and registers, performs operation on it & sends output back to registers
- registers hold any data/instructions/memory addresses about to be used by CPU, specific registers for different tasks
- input/output device
What are the major components of a CPU? (Central Processing Unit):
- Arithmetic Logic Unit
- Control Unit
- Clock
- Bus
- Cache
- registers
What does the arithmetic logic unit (ALU) do?
- complete simple addition/subtraction
- compares sizes of numbers
- can do multiplication/division using repeated addition/subtraction
- performs logic operations and binary shifts
- registers used to store immediate results if calculations
What does the Control Unit (CU) do?
- manages fetching, decoding and execution of program instructions (fetch-decode-execute cycle)
- controls flow of data inside CPU (to registers, ALU, cache)
- controls flow of data outside CPU (to main memory, input/output devices)
What does the clock do?
- sends out an electrical signal/pulses that continually cycles between 1 and 0, usually at constant rate
- signal used to synchronise when instructions will be carried out
- clock speed = no. of clock cycles executed by CPU per second
- measured in GHz
What are Buses, what do they do?
- collection of wires used to transmit data between components of CPU, and to other parts of computer system
- processor may have separate buses for carrying data, instructions and memory addresses
What is Cache? What does it do?
- very fast memory in CPU
- stores regularly used data so CPU can access it quickly
- very low capacity & expensive
What are registers? What do they do?
Registers are small amounts of high speed memory contained within the CPU. They are used by the processor to store small amounts of data that are needed during processing
5 most common registers: (in vonn Neumann)
- program counter
- memory address register (MAR)
- memory data register (MDR)
- current instruction register (CIR)
- accumulator (ACC)
What affects the performance of the CPU?
- clock speed
- no. of processor cores
- cache size
- cache type
What does clock speed do?
What is the affect of clock speed on the CPU?
- determines the no. of instructions a single core processor can carry out per second
- some CPUs can be ‘overclocked’ to make them run at a higher clock speed than factory set rate. But CPUs can overheat, causing crashes or permanent damage) so high performance cooling systems often needed
What is the affect of No. of processor cores on the CPU?
- more cores a CPU has = more instructions it can carry out at once = faster process of data
(Each core processes data independently of the rest)
What is the effect of cache size on the CPU
- larger CPU cache gives CPU faster access to more data it needs to process
What is the effect of cache type on the CPU?
- there are three levels of cache memory
- higher level = holds more but slower
- cache speed based on how far it is from CPU (L1 is on CPU, L3 is on motherboard)
What are embedded systems?
What are the properties of embedded systems?
Give some examples
= computer built into a device, dedicated systems
- RAM and ROM on same chip as CPU to reduce space/cost
- more ROM than RAM
- norm no secondary storage
- ROM stores all programs
- control systems (monitor and control memory)
Eg. Dishwasher, calculator, microwaves, washing machines
What are Non-embedded systems?
What is the memory type on them?
Give some examples
= general purpose (not dedicated)
- RAM and ROM on motherboard
- more RAM than ROM
Eg. Mobile phones, computers
What are the advantages of embedded systems over non-embedded systems?
- more efficient
- easier to design
- cheaper to produce
(Dedicated to certain tasks)
What is cloud storage?
Service where files can be uploaded via the internet to a remote server
(Usually stored on HDDs/SSDs)
Advantages of cloud storage (compared to local storage)?
- Users can access from any device
- files can be shared/made public
- easy to increase amount of storage available
- no expensive hardware/IT staff needed
- host provides security and backups for you
- can be cheap if not much storage needed
Disadvantages of cloud storage (compared to local storage)
- need connection to internet
- upload/download speed depends on bandwidth
- depends on host for security & backups
- can be vulnerable to hackers
- unclear ownership of data
- subscription fees for long term storage may be expensive
Describe RAM (random access memory)
= main memory of computer
- volatile (temporary) = needs power to retain data
- data files/programs stored here when used
- computer boots -> OS copied from secondary storage to RAM
- when files transferred -> secondary storage to RAM
- slower than CPU, faster than secondary storage
Describe ROM (read only memory)
- ROM chips use flash memory = non-volatile (not temporary)
- only read, not written to
- has instructions to boot up computer (BIOS - Basic Input Output System)
- more small chip in motherboard
- power on -> CPU reads instructions from ROM (CPU self checks & sets up computer)
- can update BIOS
What is the Main memory (primary storage)?
- memory areas CPU can access directly
Eg. CPU registers (MAR, MDR), cache, RAM, ROM - mostly volatile(except ROM)
- fastest read/write speeds
What is Secondary storage?
- where all data stored when not in use
- non-volatile
- much slower than main memory (primary)
Eg. Magnetic hard drives, SSDs, CDs, SD cards
Types of secondary storage:
- solid state
- optical
- magnetic
Explain the operation of Magnetic storage (HDDs = Hard Disk Drives)
- HDDs = traditional internal storage in PCs/laptops
- made up of stack of magnetised metal disks spinning at rate between 5400 and 15000 revolutions per minute
- data stored magnetically in small areas(sectors) within circular tracks
- read/write heads on moving arm used to access sectors on disks
Other types of magnetic storage
- magnetic tape
- floppy disks
Advantages of magnetic storage (HDDs)
- cheaper than SDD
- higher capacity than SDD
- longer read/write life (SDDs deteriorate after written certain no. of times
- portable HDDs popular for backing up/transporting large amounts of data
- long lasting
- reliable
Disadvantages of magnetic storage (HDDs):
- noisy
- not shock proof, can be damaged by large impacts
- not as fast as SDD
- contains moving parts = fragile
Explain the operation of Solid state storage (SDDs - Solid State Drives/USB)
- SDDs used for internal storage, no moving parts
- most use a type of flash memory
- uses semiconductor chips to store data.
Advantages of Solid state storage (SDDs)
- faster read/write times than HDD
- quicker times for booting up/opening programs/files
- don’t need defragmenting
- shock-proof
- silent
Disadvantages of solid state storage (SDDs)
- more expensive
- SDDs can only be written certain no. of times before they start to deteriorate = shorter read/write life
Other types of flash storage:
-
Explain the operation of optical discs/storage:(CDs, DVDs, Blu-Ray)
- data stored as microscopic indentations on shiny surface of disc
- data read by shining laser beam on surface and detecting changes in position of reflected beam
Comes in 3 forms
- read-only
- write-once
- rewritable
Advantages of Optical discs(CDs, DVDs, Blu-Ray)
- very cheap (per GB)
- portable
- quite robust so wont be damages by water/shocks (but easily scratched)
Average read/write speed of different types of secondary storage
(Fastest -> slowest)
SDD HDD Magnetic tape Memory/SD card Optical disc
Disadvantages of optical discs (CDs, DVDs, Blu-Ray)
- streaming/downloading is easier nowadays
- can’t compete with flash storage devices due to:
- low capacity per disc
- very slow read/write speeds
- poor reliability of RW discs
Average cost (per GB) of different types of secondary storage (Most expensive -> cheapest)
SDD Memory card HDD Optical disc Magnetic tape
Average capacity of different types of secondary storage
Highest -> lowest
Magnetic tape HDD SDD Memory card Optical disc
Fetch-decode-execute cycle
CPU read instructions stored in main memory and executes them:
Fetch:
- control unit reads memory address of next CPU instruction
- instruction stored copied from main memory to one of registers
-
Decode:
- instruction decoded by control unit
Execute:
- instruction is carried out
Eg. Data may be read from/written to main memory, calculation/logic operation (ALU), change address in CU, halt program
Flash memory:
- non-volatile memory
- stores data in electric circuits by trapping electrons
- used in USB sticks/SD cards/SSDs
How much data can __ hold?
- CDs
- DVDs
- Blu-Rays
- CDs = 700 MB
- DVDs = 4.7 GB
- Blu-Rays = 25GB
