Computer organisation and architecture Flashcards
what is a computer system?
it is any device which is able to take a set of inputs and process them into useful outputs
What is a bus?
they consist of a series of wires that transfer data signals between internal components
what are the main components of a cpu
- processor
- main memory
- address, control and data buses
- I/O controllers
What are I/O controllers used for?
- peripherals cannot directly connect to the CPU
- I/o controller acts as an interface between the device and the computer
what is a device driver?
it is the software that interacts directly with the I/O controller
What are the tasks of an I/O controller
- The controller converts the signals received from a peripheral device into a format the computer can process, and vice versa
- It receives I/O requests from the CPU, and then sends device-specific control signals to the device it is controlling
- It also manages the data flow to and from the device, freeing the CPU to get on with other tasks
What is the control bus used for?
it is used to send control signals between each I/O controller and the processor, and between the processor and memory
What is the use of the data bus?
sends data between CPU components
What is the use of the address bus?
it sends memory addresses from the processor to CPU components
the system bus comprises of three different buses
What do control signals consist of ?
- Memory read
- Memory write
- Bus request
- Bus grant
- Clock
What does the “memory read” control signal do?
causes data from the addressed location to be placed on the data bus
What does the “memory write” control signal do?
causes data on the data bus to be written into the addressed location
What does the “Bus request” control signal do?
indicates that a device is requesting use of the data bus
What does the “Bus Grant” control signal do?
indicates that the CPU has granted access to the data bus
What does the clock do?
it is used to synchronise operations
Memory is divided up into equal units called …
Words
Properties of the data bus
- it is bi-directional as data can be sent both ways along the bus
- the width of the data bus is defined by the amount of wires it contains
- if the data bus is the Same width as a computer word, data can be transferred in a single operation
- bus width affects overall system performance
Properties of address bus
- carries the address of a memory location in one direction from the processor to I/O controllers and memory
- the width determines the maximum possible memory addresses of the system
- a 32-bit bus can carry 232 addresses
properties of main memory?
- stores data and instructions that are to be processed
- the number of memory addresses is constrained by the width of the address bus
- each address can store a fixed number of bits determined by the type of processor
- smallest addressable unit is a word
What is the stored program concept
- it is when computers are designed to allow data and instructions to be stored
How does the stored program concept work
- Machine code instructions are loaded into main memory to be executed by the processor
- the instructions are fetched one at a time and executed immediatley by the processor in a sequential order
How does the von Neumann architecture use the stored program concept
- instructions and data are stored in a common main memory and transferred using a single shared bus
properties of Harvard architecture
- different sized memory spaces and word lengths can be used for data and instructions
- commonly used in embedded systems performing specialist functions rather than general purpose machines
- used when speed takes over priority over the complexities of design
What is the role of the arithmetic logic unit (ALU)?
- performs arithmetic , logical and shit operations on data
What is the control unit?
it is the part of the processor that coordinates the activity of all other components
How does the control unit function?
- each instruction is accepted and decoded
- separate steps such as fetching the address of data, and fetching the data itself from memory are identified
- each step is synchronised with a regular pulse from the system clock
What is the system clock
A series of ON/OFF signals are used to synchronise the operations of the processor components
- actions are usually carried out on the rising edge of the clock
- actions take a fixed number of cycles to complete
use of general purpose registers
- rather than writing data back to slow memory it can temporarily be stored in the super-fast processor registers
- processor is then able to access and re-use these results in subsequent calculations
how are instructions executed?
- carrying out sequences of programming instructions requires many different snippets of information
- the processor has to temporarily hold the current instruction to be executed
- it has to hold the address of the data that it needs, and the data itself
- it has to keep track of the address of the next instruction to be executed
Program Counter (PC)
Holds the memory address of the next instruction to be executed
Current Instruction Register (CIR)
Holds the current instruction
Memory Address Register (MAR)
holds the address in memory where the processor is required to fetch or store data from or to
Memory Buffer Register (MBR)
temporarily holds data moving between the processor and main memory
Status Register (SR)
Holds information about the current state of operations. it is used to set flags or to detect error conditions
what occurs at the Fetch stage of the CPU cycle
- address of the next instruction transferred from PC to MAR
- PC is incremented by 1
- instruction stored in location addressed by MAR is transferred to MBR
- instruction transferred from MBR to CIR
What occurs at the Decode state of the CPU cycle
- Instruction in CIR is decoded
- additional data, if required by the instruction is fetched from memory
- and passed to registers
What occurs at the Execute stage of the CPU cycle
- instruction is executed by the ALU
- registers are used to store intermediate data or results
- the result is stored in the accumulator or general purpose register or memory
Hows does clock speed affect CPU performance
- the faster the clock speed, the faster a computer can fetch, decode and execute instructions
What is cache
it is a small amount of super fast memory that stores data that is frequently used by the processor
- larger and slower than a register, faster and smaller than RAM
- can improve processing speed
Hows does the number of cores affect processor performance
more processors can be linked together on a single chip allowing more instructions to be executed simultaneously
How does Word length affect performance of a processor
the amount of data that the CPU can process simultaneously
How does address and data bus width affect processor performance
- increasing the width of the address bus allows more possible memory addresses of the system
- increasing the width of the data bus allows more data to be transferred in a single operation
what is the instruction set of a processor
describes the commands a processor can perform. varies depending the processor which is used
what is machine code
it consists of pure binary and is the only language that the processor is able to understand
What does the opcode include
- the actual command for the computer to perform
- the addressing mode - specifies whether the operand is the actual data, memory address or a register
*
What does the opcode include
- the actual command for the computer to perform
- the addressing mode - specifies whether the operand is the actual data, memory address or a register
*
What does the operand include?
- one or more items in data that are to be used in the instruction
what is the addressing mode
specifies which type of data is being used, immediate addressing and direct addressing
what is immediate addressing mode
- the operand is the actual value, the addressing mode 00 data is a value, not an address
What does direct addressing mode consist of
- the operand in this case is the address of the location in memory of the data to be used
- the addressing mode 01 specifies that the data is an address not a value
how do barcode readers work
- light from a laser is directed at a pattern and a sensor detects the intensity of light that bounces back
- the black bars will absorb more light giving a binary reading of 0
- the white bars will reflect giving a binary reading of 1
- the patterns of 1’s and 0’s create a unique identity
What are two common types of barcode systems and what are their uses?
- UPC-A/EAN
- used in retail and warehousing
- Code 128
- Used in transport and shipment tracking
What is a benefit of using code 128 over UPC-A/EAN
code 128 is able to represent letters and numbers whilst UPC-A/EAN can only represent numeric digits
How is a UPC-A/EAN barcode formed?
- long guard bars to show the start and end of the barcode and also central guard bars to distinguish left uniquely from right
- uses 7 bar elements to form four alternating dark and light bards of varying thicknesses to represent each data between the guard bars
UPC-A barcode anatomy
What are QR codes?
- they are used in 2D barcodes and can be read by smartphones or tablets
- contain - links to websites, information
- used in
- restaurant coupons
- mobile concert tickets
- aeroplane tickets
How do digital cameras capture data?
- the shutter opens to let light onto a charge-coupled device or complementary metal oxide semiconductor sensor at the back of the lens
- the intensity of light is measured by millions of tiny sensors arranged in a grid on the sensor
- light levels for each pixel are represented as binary values
- this information is now stored as an image in the cameras memory
How do digital cameras sense colour?
- RGB filters are used with different sensors in the camera to separate out these wavelengths
- the intensity of each of these colours falling is measured and stored to produce an RGB value
How do laser printers operate?
- a print drum is given a negative static charge
- a laser shines a reverse image of the page at the drum
- laser light reverses the charge on the drum
- toner is charged negatively and sticks to positively charged image
- toner is transferred from drum to the paper and fused using a heat roller
How do Radio Frequency ID systems work? (RFID)
- The powered receiver emits radio frequency energy
- the transponder antenna in the bank card, mobile phone or tag becomes energised by radio waves
- the transponder can then send data to the reciever
What are the uses of RFID tags?
- security control points or identification of people, animals, goods or valuables
- shipping and supply chain tracking for goods
- banking and fast payments
- as a potential replacement for barcode systems
What is a passive and active tag (RFID)?
- a passive transponder have no power source themselves, they rely on the radio waves received for their energy. they need to be placed near the receiver
- active tags use a larger battery powered beacon which can broadcast its own signal rot receivers up to 300m away. useful for larger items that are not place on a receiver by hand.
What is primary storage?
it is volatile and usually refers to RAM
What is secondary storage?
refers to non-volatile storage
- magnetic storage e.g. HDD
- optical storage e.g. CD
- flash memory e.g. SSD
