Section 5 - Computer organisation and architecture Flashcards
(31 cards)
what are the internal components of a computer
- processor
- main memory
- address bus, control bus, data bus
- I/O controllers
what is the processor
the processor responds to and processes the instructions that drive the computer
what parts are in the processor
- control unit
- ALU (arithmetic/logic unit)
- registers
- clock
what does the control unit do
co-ordinates and controls all the operations carried out by the computer
e.g. FDE
what does the ALU do
the ALU can perform different operations on data
what are registers
memory cells that operate at high speeds
an accumulator is another word for general purpose register, only really used when there is just one register
what is a bus
a set of parallel wires connecting two or more components of a computer
what are the different buses for
- address bus: if the CPU wants to access a particular main memory location
one way (from processor to memory or I/O controller) - data bus: moves around data
travels in both directions - control bus: moves around control signals
travels in both directions
what is an I/O controllers
a device which interfaces between an input or output device and processor
what is von Neumann architecture
a shared memory and control bus is used for data and instructions
what is the stored program concept
instructions are stored in main memory and fetched and executed by the processor
what is Harvard architecture and advantages
computer architecture with separate memories and buses for instructions and data
used with digital signal processing (DSP) systems
- means instructions and data can be accessed simultanously
- avoids delays to fetch information
- data and memory can have different word lengths
what are the dedicated registers
- program counter (PC): stores the address of the next instruction to executed
- current instruction register (CIR): holds the current instruction being executed
- memory address register (MAR): holds the address of the memory location of the data being executed on
- memory buffer register (MBR): temporarily stores data read or written from memory
- status register (SR): contains bits that have been set or cleared
what happens in the fetch stage of the FDE cycle
- the address of the next instruction is copied from the PC to the MAR (via the address bus to main memory)
- the instruction held at that address moved to the MBR (via the address bus)
- the contents of the PC is increased by 1
- the contents of the MBR are copied to the CIR
what happens in the decode stage of FDE cycle
- the instruction held in the CIR is decoded by the control unit
- the instruction is split into opcode and operand
- additional data is fetched is necessary and passed to registers
what happens in the execute stage of the FDE cycle
- the instruction is executed, and any calculations needed are carried out by the ALU
- results are stored in the accumulator, general purpose register or memory
what are the factors affecting processor performance
- number of cores: more cores means more FDE cycles
- amount of cache memory: cashe has very fast read/write speeds, reduces time wasted fetching information from main memory
- clock speed: higher frequency of signals means FDE cycles completed in a shorter amount of time
- word length: longer word length means more bits transferred in the same amount of time
what is the difference between direct and immediate adressing
in immediate addressing the operand is the actual value
in direct addressing the operand holds the memory address of the value
what are the four types of barcode readers
- pen-type readers
- laser scanners
- charge-coupled device (CCD) readers
- camera-based readers
how do pen-type readers work
- a light source and photo diode are placed next to each other in the tip of a pen
- the tip of the pen is dragged across the bars and the photo diode measures the intensity of the light reflected back from the light source
- dark bars absorb light and space reflects light
- the waveform generated is converted to a digital pattern
how do laser scanner barcode readers work
- has a laser beam and photo diode
- a laser beam reflects off a moving mirror
- the photo diode measures the intensity of the light reflected back from the laser
- dark bars absorb light and spaces reflect light
- the waveform generated is converted to a digital pattern
- the mirror means the barcode can be read in many positions
how do charge couple device (CCD) readers work
- hundreds of arrays of tiny light senses are lined up in a row in the head of the reader
- each sensor measures the intensity of the light immediately in front of it
- the sensors generate a voltage pattern of the barcode
how do camera based barcode readers work
- camera and image processing techniques are used to decode the barcode
how do digital cameras work
- a digital camera uses a CCD or CMOS sensor with millions of tiny light sensors arranged in a grid
- the shutter opens, light enters the camera onto the sensor on the back of the lens
- each sensor measures the brightness of each pixel and turns the light into electricity, storing the amount of charge
- to record colour, the sensors are placed under colour filters to filter out the wavelengths
- the binary data is recorded onto the memory card
