Computer organisation and architecture

Question 1

What is the data bus

Answer 1

Transfers data between the processor and memory
bi-directional

Question 2

What is the address bus

Answer 2

Used to specify a physical address in memory, so that the data bus can access it.
Goes from CPU to Memory
uni-directional

Question 3

What is the control bus?

Answer 3

a bus that controls the flow of data between the processor and other parts of the computer
bi - directional

Question 4

What is von Neuman architecture

Answer 4

a technique for building processors where data and instructions are stored in the same memory and accessed via buses

Question 5

What is Harvard architecture?

Answer 5

A technique for building a processor, that uses separate buses and memory for data and instructions.

Faster as has multiple buses
data can not be written in the wrong location

Question 6

What is the stored programme concept?

Answer 6

The idea that instructions and data are stored together in memory

Question 7

What is a clock

Answer 7

a device that generates a signal that synchronise the components of a computer

Question 8

What is a register

Answer 8

a section of storage that is part of the processor

Question 9

What is the status register

Answer 9

a register that keeps track of the status of various parts of a computer.

Question 10

What is the interrupt register

Answer 10

stores details of oncoming interrupts

Question 11

What is the current instruction register CIR

Answer 11

a register that stores instructions that the CPU is currently decoding/executing

Question 12

what is the programme counter

Answer 12

a register that stores the address of the next instruction to be taken from main memory into the processor.

Question 13

What is the memory buffer register

Answer 13

a register that holds data that is ether written to, or copied from the CPU.

Question 14

What is the memory address register

Answer 14

a register that stores tge location of the address that data is either written to, or copied from, by the processor.

Question 15

How does the fetch decode execute cycle work?

Answer 15

Fetch.
- The PC holds address of the next instruction
- this is sent along the address bus to main memory.
- the contents of this location are sent via the data bus to the CIR and the PC is incremented.
- the details are loaded into the MAR and the data is sent to the MBR
Execute.
- the instructions are taken to the CIR and decided what they should do by referring to the instruction set.
- once it has been decoded, it is executed

Question 16

What factors affect performance

Answer 16

• clock speed
• bus width (the number of bits that can be sent down a bus in one go)
• word length ( the number of bits that can be addressed, transferred or manipulated as one unit.

Question 17

How does an interrupt work?

Answer 17

after an instruction is executed, the interruption register is checked.
If one has occurred, a routine is called to handle the interrupt.

Question 18

How does a digital camera work?

Answer 18

• The shutter is opened, and light is let in through the lens.
• the light is focused onto a CCD or CMOS sensor.
• These are made of transistors each which stores data for the pixels.
• As the light hits the sensor it is converted to electrons and the amount of charge is recorded.
• To record colour it has to use three sensors (RGB)

Question 19

How does a barcode reader work?

Answer 19

• a light source is passed over a barcode
• some sensor is used to measure the light reflected back.
• The white parts reflect the most light whereas the black parts do not, so it is possible to distinguish patterns
• the pattern is converted using an ADC
• the signal is decoded and interperreted.

Question 20

How does RFID work?

Answer 20

• The tag contains a chip, which contains data about the item, as well as modem to modulate and demodulate radio signals.
• Tags can be active or passive.
• Signals can be transmitted in both directions using radio frequencies

Question 21

How does a laser printer work?

Answer 21

• a rotating drum inside the printer is coated in a chemical which holds an electrical charge.
• a laser is reflected onto the drum, and where the light hits, the drum is discharged
• as the drum rotates, toner is picked up, and attracted to the charged part of the drum.
• paper is charged and passed over the drum, it attracts toner
• The paper is heated, to fuse the toner.

Question 22

How does a magnetic hard disk work?

Answer 22

• made of a number of disks in a stack and coated in a magnetic material, changes in magnetism represents 1s and 0s.
• They spin at speeds between 3600-12500 RPM as read write heads read from, and write to the discs.
• An actuator arm moves the heads

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Question 23

How does an optical disk work?

Answer 23

• Made up of lands, and pits and a laser reads how much light is reflected back, to decode 1s and 0s.
• For writeable optical disks, it uses a dye instead, and the laser alters the state of the dye.