Computer Organisation and Architecture (7.4 missing)

What is main memory?

made up of RAM and ROM, storing program instructions and frequently used data

What is a bus?

a series of parallel wires connecting internal components

What is the role of the address bus?

transports memory addresses, specifying where memory data is to be sent or retrieved from

What is the role of the data bus?

sends data and instructions to and from components of the computer

How does adding a single wire affect amount of addressable memory locations?

doubles

What is the role of the control bus?

carries control signals to regulate operation of the computer system and carries the clock signal

What are I/O controllers?

hardware that controls the communication of data between the processor and external devices

What is harvard architecture and its uses?

• the processor uses two separate memory locations and buses for instructions and data

• instruction memory can be made read-only - more secure

• used in embedded systems

What is Von Neumann architecture?

• instructions and data are stored together in the same memory, same buses

• used in general purpose computers

What is the stored program concept?

machine code instructions stored in main memory are fetched and executed serially by a processor the performs arithmetic and logical operations

What is the ALU?

performs arithmetic and logic operations

What is the role of the control unit?

responsible for controlling components and the fetch-execute cycle

What are registers?

tiny memory locations used to hold data temporarily with high read and write speeds

What is the role of the program counter?

holds the memory address of the next instruction to be executedW

What is the role of the current instruction register?

holds the instruction currently being executed by the processor

What is the role of the memory address register?

stores the memory address of a memory location that is to be read or written to

What is the role of the memory buffer register?

holds the contents of the memory location read from or to be stored

What is the role of the status register?

contains bits which can change to indicate an interrupt

What is the clock?

generates a time signal which changes at a regular frequency to synchronise communication

What happens in the fetch stage?

• contents of PC copied to MAR

• content of the MAR transferred to memory by the address bus

• data is sent from memory to the MBR by the data bus

• PC incremented by one

• content of MBR copied to the CIR

What happens in the decode stage?

• contents of the CIR is decoded by the control unit

• instruction split into opcode and operand

What happens in the execute stage?

• any extra data required is fetched from memory

• instruction is carried out

• results are stored in general purpose registers or main memory

When are interrupts checked for?

between each execute and fetch stage, the contents of the status register is checked for changes

What is the processor instruction set?

the group of instructions that a processor can carry out

What is immediate addressing?

the value in the operand is the actual value to be usedW

What is direct addressing?

the value in the operand is the address in memory of the data to be used

What happens when an interrupt occurs?

processor stops executing the current programs and handles the interrupt

What factors affect processor performance?

• number of cores

• cache memory

• clock speed

• word length

• bus width

How does number of cores affect processor performance?

each core can perform its own fetch-execute cycle independently of others

How does cache memory affect processor performance?

more memory with faster read and write speeds

How does clock speed affect processor performance?

higher frequency of pulses means more cycles in the same period of time

How does word length affect processor performance?

allows more bits to be transferred as one unit

Explain barcodes and readers

barcode - consists of dark and light portions

reader - laser, lens, photodiode and mirror

• mirror directs light from the laser onto a printed barcode

• light reflected passes through the lens and hits the photodiode

• which turns light into charge that can be measured into a digital signal

Explain how digital cameras work

• the lens focuses light onto the sensor, controlled by the shutter

• sensors convert light into charge

• charge builds in each cell for each pixel which is measured for a digital value

• for colour, each pixel has multiple cells with a filter allowing certain colours of light

Explain how a laser printer works

• the drum is positively charged all over

• areas where the laser hits are discharged, leaving an impression of charge

• the toner roller dispenses charged toner onto the drum

• the toner is attracted to the positive charge on the drum

• toner is applied to the paper and heated by fusers

Explain RFID tags

contain a chip of small memory

coil of wire acting as an antenna

usually passive, inducing enough power from the reader

can be active using small battery

Explain how RFID works

• the reader emits radio waves picked up by the antenna

• the power induced by these is enough to power the passive chip

• the chip’s antenna emits a radio wave containing its information

• picked up by the reader which decodes the information

Explain how solid state drives work

• consists of non-volatile NAND flash memory cells and a controller

• memory cells of floating gate transistors which trap electrical charge

• data stored in pages which form blocks

• data cannot be overwritten so must be completely erased before new is added

What are advantages and disadvantages of solid state drives?

• relatively low capacity

• very high speed

• low latency

• lightweight and portable

• low power consumption

Explain optical disks

• can be read-only, recordable or rewritable

• pits and lands are burnt into the disk using a high power laser which deforms the surface

• read by a low power laser, light reflects onto a photodiode on a land and the pattern converts to digital signals

Explain rewritable disks

a pattern of reflections and scatters are created by a dye - either absorbed or reflected

recordable disks use photosensitive dye - change from opaque to transparent under a laser

What are advantages and disadvantages of optical disks?

• very low capacity

• low speed

• high latency

• small and lightweight

• can be damaged by scratches and dirt

• high power consumption

Explain hard disk drives

• consists of multiple circular platters of magnetic material

• above each platter is an actuating arm where the read/write head is on

• read/write head changes the polarity of the platter

• data is written in concentric tracks and further split into sectors

Explain advantages and disadvantages of hard disk drives

• high capacity

• good speeds

• high latency

• bulky, heavy and easily damaged

• high power consumption

What is the stored program concept?

machine code instructions are stored in main memory

fetched and executed serially

by a processor which carries out arithmetic and logical operations