Central processing unit/architecture | 9618 P1 CS

What is the control unit and what does it do?

- Directs and coordinates other parts of the computer system
- Controls operations of computer systems
- fetches computer instructions
- decodes each instruction
- executes these instructions

What is the arithmetic logic unit and what does it do?

- performs arithmetic operations and bit shifting operations
- performs logic operations
- designed to perform integer calculation

What are registers?

- small pieces of memory
- part of the processor
- temporary storage of data which is about to/has been processed

What is the difference between a general purpose and special purpose register?

- General purpose registers hold the temporary data while performing different operations
- Special purpose registers hold the status of a program

What does the program counter do?

Holds the address of the next instruction to be fetched

What does the MAR do?

Stores the memory address where the data is to be read from

What does the MDR do?

Stores data that has just been read from the memory

What does the CIR do?

Holds the current instruction being executed

What does the index register do?

Used for indirect addressing

What does the accumulator do?

Stores the results of calculations carried out by the ALU

Describe the purpose of status register

-contains information about the state of the processor
- the status registry is interpreted as independent flags
- each flag is set depending on an event.

What is a system clock?

- internal clock that regulates the rate at which the instructions are executed
- CPU requires a fixed number of clock cycles to execute each instruction
- used to synchronize all of the operations

How is data transferred between various components of the computer system?

Data buses

List the types of buses.

- Data bus
- Control bus
- Address bus

How is data transferred through a data bus?

- Data bus carries data between the processor and memory
- bi-directional bus used to exchange data

How is data transferred through a control bus?

- transmits signals between the control unit and other components
- bidirectional

How is data transferred through an address bus?

- uni-directional bus
- carries signals related to memory address between the processor and memory

What are the factors affecting the computer's performance?

- data bus width
- clock speed
- cache memory
- number of cores

How does data bus width affect a computers performance?

- width determines the number of bits that can be simultaneously transferred
- increasing the width increases the number of bits that can be transferred
- hence improves processing speed as fewer transfers are needed

How does clock speed affect a computers performance?

- one F-E cycle is run on each clock pulse
- clock speed dictates the number of instructions that can be run per second
- the faster the clock speed the more instructions can be run per second

How does cache memory affect a computer's performance?

- since cache uses SRAM, it has faster access time as there is no need for refreshing
- cache memory stores frequently used instructions and data that needs to be accessed faster

What are ports?

A computer uses ports to connect with peripheral devices
(female part of connection)

What are the benefits of connecting peripheral devices using a USB port?

- fast data transfer
(useful when transferring large files, such as video files)
- automatic connection/plug and play
(hence, no need to install separate drivers)
- USB ports are industrial standards
(all new computers have a USB port)
- Device may be powered through USB
(external device could be charged while working on the computer)

What is HDMI used for?

Digital connection - video + sound

- allows us to connect multiple monitors
- allow us to output both audio and visual
- they support high definition signals
- faster data transfer
- HDMI increases the bandwith making it possible to supply the necessary data for high-quality sound and visual effects

What are the advantages of HDMI?

- current standard for modern televisions and monitors
- allows for a very fast data transfer rate
- improve security (helps prevent piracy by the help of HDCP)
-

What are the disadvantages of HDMI?

- easy to break connection while moving devices
- Limited cable length

What does VGA stand for and what is it used for?

The Video Graphics Array connector is a standard connector used for computer video output.

What are the advantages of VGA?

- simpler technology
- only one standard available
- easy to split the signals and connect a number of devices from one source
- very secure connection
- higher refresh rate

What are the disadvantages of VGA?

- does not support audio
- outdated
- modern laptops and computers rarely have VGA ports
- easy to bend the pins when making connections

Describe the fetch-execute cycle..

1) PC holds the address of the next instruction to be fetched
2) the address in the program counter is copied to the MAR
3) program counter is incremented
4) The instruction is copied from the address stored in MAR to MDR
5) instruction from the MDR is copied to the CIR

Summary
MAR <---- [PC]
PC <---- [PC + 1]
MDR <---- [[MAR]]
CIR <---- [MDR]

MAR <---- [PC]
PC <---- [PC + 1]
MDR <---- [[MAR]]
CIR <---- [MDR]

State the purpose of the double brackets in the 3rd instruction.

It shows that the content of the MAR is an address. The contents of that address is transferred to MDR.

What is meant by interrupt?

- a signal from a device/source telling the processor that attention is needed

What is an example of hardware interrupt?

- printer runs out of paper
- no CD in drive

What is an example of software interrupt?

- runtime error
- a running program needs input

Explain how interrupts are handled during the F-E cycle

- CPU carries out the F-E cycle
- an interrupt occurs
- one bit in the interrupt register would change it's status
- at the next F-E cycle, the interrupt register is checked bit by bit
- the contents would indicate an interrupt occured and it needs servicing
- CPU would either service the interrupt or ignore it for now (depending on it's priority)
- once the interrupt is serviced by the CPU, it stops its current task and control is transferred to the interrupt handler
- once the interrupt is fully serviced, the regster is reset and the contents of registers are restored