2.3 Fundamentals of computer organisation and architecture Flashcards
Define processor
A device that carries out computation on data by following instructions in order to produce an output. Electrical pulses timed by the computer’s clock are controlled by transistors which represent parts of an instruction being carried out
Define main memory
Stores data and instructions that will be used by the processor
Define fetch execute cycle
The continuous process carried out by the processor when running programs
Define RAM
Random Access Memory (RAM) stores data and can be read from and written to. This memory is volatile, meaning that if it data stored on it is not saved before the computer is shut down the data will be lost
Define ROM
Read only memory (ROM) stores data and can be read from but cannot be written to. This is often used to store instructions relating to the setup of the computer
Define bus
Microscopic parallel wires that transmit data between internal components
Define data bus
Transfers data between the processor and memory
Define input/output controller
Controls the flow of information between the processor and the input and output devices
Define word length
The number of bits that can be addressed, transferred, or manipulated as one unit
Define address bus
Used to specify a physical address in memory so that the data bus can access it
Define addressable memory
The concept that data and instructions are stored in memory using discrete addresses
Define control bus
Controls the flow of data between the processor and other parts of the computer
Define Von Neumann architecture
A technique for building a processor where data and instructions are stored in the same memory and accessed via buses
Define Harvard architecture
A technique for building a processor that uses separate buses and memory for data and instructions
Define stored program concept
The idea that instructions and data are stored together in memory
Describe the stages of the fetch execute cycle
- Fetch: the processor fetches the program’s next instruction from memory. The instruction will be stored at a memory address and contain the instruction written in binary code
- Decode: the processor works out what the instruction at that binary address means
- Execute: the processor carries out the instruction, this encompasses tasks such as reading data from memory, performing a calculation, or writing data to memory
Define control unit
The part of the processor that manages the execution of instructions
Define arithmetic logic unit
The arithmetic logic unit (ALU) is the part of the processor that processes and manipulates data
What is the clock?
A device that generates a signal used to synchronise the components of a computer
Define register
A small section of temporary storage that is part of the processor, which stores data or control instructions during the fetch execute cycle
Define status register
Keeps track of the various functions of the computer such as if the result of the last calculation was positive or negative
Define interrupt register
Stores details of incoming interrupts
Define current instruction register (CIR)
Register that stores the instructions that the CPU is currently decoding / executing
Define program counter (PC)
Register that stores the address of the next instruction to be taken from main memory into the processor
Define memory buffer register (MBR)
Register that holds data that is either written to or copied from the CPU, this can also be known as the memory data register (MDR)
Define memory address register (MAR)
Register that stores the location of the address that data is either written to or copied from by the processor
How does the fetch execute cycle work with respect to registers?
Fetch:
- PC holds address of next instruction
- Processor sends this address along address bus to main memory
- Contents of memory location at that address sent via data bus to CIR and PC is incremented
- Details of addresses loaded into MAR and data sent to MBR
Execute:
- Processor takes instruction from CIR and decides what to do with it with reference to an instruction set
- Processor carries out the instruction
Define bus width
The number of bits that can be sent down a bus in one go
Define multi-core
A chip with more than one processor
Define cache
A high speed temporary area of memory
What are the factors that affect processor performance?
- Clock speed: This indicates how fast an instruction will be executed, meaning that increasing clock speed increases the theoretical speed at which the computer processes instructions
- Bus width: Increasing bus width means that more bits can be passed down the data bus with each pulse of the clock, increasing the speed at which data can be transferred and therefore that instructions can be processed at
- Word length: Computer systems with greater word length can have more bits of data transferred with each speed of the clock, increasing the speed of the processor
- Multiple cores: A core is defined as the component of a processor which allows for instructions to be fetched and executed, by increasing the number of cores, the number of instructions that can be processed at any given time is increased, improving processor performance
- Cache memory: Instructions and data that are used frequently are stored in a temporary area of memory separate from main memory that can be accessed much more quickly, meaning that by storing the most commonly used functions and data in cache memory, the processor speed increases
Define interrupt
A signal sent by a device or program to the processor requesting its attention
Define interrupt service routine (ISR)
Calls the routine required to handle an interrupt
Describe the interrupt service routine
Following the execute stage of the fetch execute cycle, the processor will check for interrupts. If one has occurred, the processor will stop current tasks to handle the interrupt with the interrupt service routine (ISR), which calls the routine required to handle the interrupt
Define priorities
A method for assigning importance to interrupts in order to process them in the right order
Define vectored interrupt mechanism
A method of handling interrupts by pointing to the first memory address of the instructions needed
Define instruction set
The patterns of bits that a processor recognises as commands, along with their associated meanings
Define opcode
An operation code or instruction used in assembly language
Define operand
A value or memory address that forms part of an assembly language instruction
Define addressing mode
A way of programming using mnemonics such as LDR, ADD
What is the difference between direct and immediate addressing?
In direct addressing, the operand is the memory address or register number, whereas with immediate addressing, the operand is the datum
Define data transfer operation
Operations within an instruction set that move data around between the registers and memory
Define arithmetic operations
Operations within an instruction set that perform basic maths such as addition and subtraction
Define shift instructions
Operations within an instruction set that move bits within a register
Define logical operations
Operations within an instruction set that move the bits around within the operand
Define branch operations
Operations within an instruction set that allow you to move from one part of the program to another
How does a digital camera function?
- Shutter opens and lets light through the lens
- Light is focused onto a sensor
- Sensors made up of transistors which each store the data for one or more pixels
- As light hits the sensor, the charge of the photons hitting the sensor is recorder for each pixel
- Colours can be created as RGB values from either 3 different sensors or 3 different filters
- Data is typically stored on removable storage devices using programmable ROM
- Data is often stored in a compressed file such as JPG or PNG, however raw files can also be generated
- The digital data can be decoded and manipulated using software
How do barcode readers function?
- Light, usually LED or laser, is passed over an image
- A sensor measures the intensity of light reflected back, this generates a current and can be used to create a waveform
- White areas reflect the most light and black the least, giving distinct black and white bars
- The analogue waveform can be converted to a digital signal with an analogue digital converter (ADC)
- This can be converted to a binary code e.g. where black = 0 and white = 1
- The signal is encoded into a form that can be interpreted by the relevant software
What is radio frequency identification (RFID)?
A microscopic device that stores data and transmits it using radio waves, usually used in tags to track items
How does RFID function?
- The tags contain a chip that contains data about the item and a modem to modulate and demodulate the radio signals
- It also contains an antennae to send and receive signals
- Tags can be active (have their own power source) or passive (will pick up electromagnetic power when in range of an RFID reader)
- Signals and data can be transmitted in both directions using radio frequencies
- Tags can be used to track the physical location of the item or the item can transmit data back
What is a laser printer?
A device that uses lasers and toner to create mono and colour prints
How does a laser printer function?
- A rotating drum inside the printer is coated in a chemical which holds an electrical charge
- The laser beam is reflected onto the drum and where the light hits the drum the charge is discharged, creating the image on the drum
- As the drum rotates it picks up toner which is attracted to the charged part of the drum
- Paper is passed over the drum and by charging the paper with the opposite charge to the toner, the toner is attracted to the paper and away from the drum
- The paper is heat treated to fuse the toner onto the paper
Define hard disk (HDD)
A secondary storage device made up of metallic disks that stores data magnetically
How does a hard disk (HDD) function?
- Constructed of hard metallic material and are sealed to prevent corruption, are often made up of disks arranged in a stack
- Disks are coated with a magnetic material such that changes in the magnetism denote 0s and 1s
- Read / write heads do not touch the surface of the disk but instead float slightly above it; between the lateral movement of this arm and the rotation of the disk, the heads can access every part of the disk
- Disks are organised into concentric tracks which can each be individually addressed
Define controller
In SSD’s a controller is needed to organise data into blocks for storage purposes
Define block
In data storage it is the concept of storing data into set groups of bits and bytes of a fixed length
Define floating gate transistor
In SSD’s it is a type of non-volatile transistor that stores data even without a power source
How does an optical disk function?
- Made up of one single spiral track that starts in the centre and works its way to the edge of the CD
- Laser will read data by reading the pits and lands of the disk in combination with a sensor that measures how much light is reflected
- These are interpreted as electrical signals and can be converted into binary codes to reproduce the data on the disk
- For read only disks, when data is encoded as the series of pits and lands a protective layer is then put on the disk to prevent corruption of the data
- Writeable optical disks use a photosensitive dye instead of pits and lands; the laser will alter the state of a dye spot to change the amount of light it reflects in order to write data
How does a solid state disk (SSD) function?
- Blocks of a set physical size will be made up of data, which can only be accessed in these blocks
- Semiconductors can retain their memory due to use of floating gate transistors which can trap and store charge
- A floating gate transistor is made up of a floating gate and a control gate; a thin layer of oxide is place between the gates, trapping the charge inside the floating gate
- SSD’s use programmable ROM chips and often use a type of memory called NAND memory which organises the data into blocks and uses a controller to manage them
Compare the 3 main storage devices of HDDs, SSDs, and optical disks
- Typical capacity: HDD has the highest capacity, SSD has medium capacity, and optical disks have the lowest capacity
- Relative cost: Optical disks are the cheapest, SSDs are the most expensive, and HDDs are inbetween
- Portability: Optical disks are very easily portable, whereas specific external HDDs and SSDs are needed to be portable
- Relative power consumption: HDDs and optical disks have high power consumption compared to SSDs
- Relative access speed: SSDs have the highest access speeds, optical disks the lowest, and HDDs inbetween
- Latency: SSDs have low latency, HDDs have high latency, and optical disks very high latency
- Reliability: Optical disks have fair reliability, HDDs have good reliability, and SSDs very good reliability
- Relative physical size: HDDs and optical disks are relatively large, whereas SSDs are comparatively small
