Computer Science - The characteristics of contemporary processors, input, output and storage devices

Question 1

What is the processor also known as?

Answer 1

• The Processor is also known as the CPU

Question 2

What is the processor responsible for?

Answer 2

• It is the internal hardware component of the computer that is responsible for executing specific instructions
• It is made up of several components, each with a specific role.

Question 3

What is the processor made of?

Answer 3

• It is made up of several components, each with a specific role. These components are The Arithmetic logic unit, the control unit, as well as various registers.

Question 4

What is the Arithmetic and Logic unit responsible for?

Answer 4

• Responsible for arithmetic calculations and logical operations

Question 5

What Operations does the Arithmetic Logic Unit carry out?

Answer 5

• These operations include:
  ○ Addition, Subtraction, multiplication,
  division
  ○ Logical bitwise operations, such as AND,
  OR, NOT and XOR
  ○ Comparisons between values, such as
  greater than, less than, equal to
  ○ Shifting binary patterns to the left or right

Question 6

What is the control unit in charge of?

Answer 6

• in charge of organising the sequence in which programme instructions are executed

Question 7

What does it mean when the control unit decodes an instruction?

Answer 7

• Decoding an instruction means that the opcode and operand of an instruction are analysed to determine what needs to be done to execute the instruction

Question 8

What is the control unit responsible for?

Answer 8

• It is responsible for directing the operations of all the other components of the processor
• It is responsible for using signals to enable data to be read, decoding every instruction that the processor will execute, organising the sequence of micro-operations that need to be performed in order to carry out an instruction and controls signals to determine the operation the ALU will carry out at each instance

Question 9

What does it mean when the control unit decodes an instruction?

Answer 9

• Decoding an instruction means that the opcode and operand of an instruction are analysed to determine what needs to be done to execute the instruction

Question 10

What is the control unit responsible for?

Answer 10

• also in charge of decoding the instructions

Question 11

What is the system clock?

Answer 11

• The system clock generates regular pulses to synchronise the operations of the processor components

Question 12

What are the two types of pulses?

Answer 12

A ‘rising edge’ is a change from a low state to a high state
A ‘falling edge is a change from a high starte to a low state

Question 13

What is the clock period

Answer 13

The time taken between two sequential rising edges is called the clock period

Question 14

What does one clock period correspond to?

Answer 14

One clock period corresponds to one clock cycle

Question 15

How many clock cycles are required for a single operation?

Answer 15

• a single operation of the processor typically requires a number of clock cycles

Question 16

What is the clock rate?

Answer 16

• The clock rate, clock frequency or clock speed is calculated as the number of clock cycles that can be completed in a single second

Question 17

What is the clock speed measured in?

Answer 17

• The clock speed is measured in Hz, but is usually displayed in MHz or GHz

Question 18

Where are the registers located and why are they located there?

Answer 18

• Located within the processor to provide extremely fast access

Question 19

What are Registers used for?

Answer 19

• used to temporarily store and access the results of operations

Question 20

What are the two classifications of registers

Answer 20

• can be general-purpose of dedicated

Question 21

What are dedicated registers used for?

Answer 21

• dedicated registers are processor based registers that can only be used for a specific purpose, for example the fetch decode execute cycle

Question 22

What are some examples of dedicated registers? What do they do?

Answer 22

• Some examples of dedicated registers are:
  ○ Program Counter (PC) - Holds the address of the next instruction to be executed by the processor
  ○ Current instruction register (CIR) - Holds the current instruction that the processor is executing
  ○ Status register (SR) - Used to store information about the result of the last instruction that the ALU executed
  ○ Memory Address Register (MAR) - Temporarily holds the address of the memory location that the processor needs to access
  ○ Memory Data register (MDR) - also known as the Memory buffer register, it temporarily holds the data that are read from or written to the main memory
  ○ Accumulator - Stores the result of any calculation processed by the ALU. The processor accesses other general purpose registers where temporary values are stored while calculations are completed.

Question 23

What happens every time a processor carries out an instruction?

Answer 23

Every time the processor carries out an instruction, it goes through three main stages

Question 24

What are the three stages of the FDE cycle and what happens during these stages?

Answer 24

These stages are where is fetches the instruction, decodes the instruction, and executes the instruction

Question 25

When is the Fetch-Decode-Execute cycle repeated?

Answer 25

The cycle is repeated for every instruction of every program that is run inside a program

Question 26

What does the FDE cycle apply to?

Answer 26

applies to both application and system software

Question 27

What must happen before the cycle can start?

Answer 27

before the cycle can start, the program instruction must be in machine code and the instructions must be located in the RAM

Question 28

Internal components of a computer What do the internal components of a computer consist of? What are the main components of a computer system? What connects these components

Answer 28

* The internal components of a computer system consist of the hardware required to process data and to allow the processor to communicate with other devices. * The main components of a computer system are: the Process (CPU), Main memory and Input/Output(I/O) controllers * These components are connected by high-speed communication buses

Question 29

Internal components of a computer - The processor What does the processor do? What is it designed to handle? What needs to happen to instructions before they can be used by the processor? What happens to data that needs to be processed?

Answer 29

* Processes data by executing program instructions * designed to handle machine code * instructions need to be transferred from the secondary storage into main memory * Data that needs to be processed is also loaded into main memory or provided by the input and output devices

Question 30

Internal components of a computer - Buses What do buses connect? What is a bus used for? what is a system bus? What are external buses? What is the system bus made up of in Von Neumann Architecture? What does the system bus connect?

Answer 30

* The components of a computer system are connected using buses * A bus is communication system that is used to transfer data between components. * A system bus is a set of parallel connections that allow components to communicate with each other and exchange data * External buses are used to connect the peripherals to the processor, can be serial or parallel connections * can be implemented in different ways, depending on the intended use * In Von Neumann architecture, the system bus is made up of an address bus, a data bus and a control bus * The system bus is used to connect the processor (CPU), main memory and the I/O controllers

Question 31

Internal Components of a computer - Data Bus What is it used for? is it bidirectional or unidirectional? What does the width of the data bus refer to? What does the width of the data bus determine?

Answer 31

* used to transfer data and instructions * bidirectional (allows a two-way connection between internal components of a system) * the width of the data bus refers to its number of parallel lines * the number of parallel lines determines the number of bits that can be transferred in one operation

Question 32

Internal Components of a Computer - Address bus What is it used for? Is it bidirectional or unidirectional? What does the width of the address bus refer to? What does the width of the address bus determine?

Answer 32

* Used to specify the address of a memory location to either read data from or write data to that memory location * One way connection from the processor to the address bus and a one way connection from the address to the main memory and the I/O controllers * unidirectional, meaning that it allows a processor to establish a connection with an addressable 'unit;, whether it's a memory location or an I/O controller * The width of the address bus refers to its number of parallel lines, which determines the number of bits that can be used to form and address of a memory location * The width of the address bus determines the maximum number of addressable memory locations

Question 33

Internal Components of a computer - Control Bus What are control buses used for? What do they manage? What do control signals to? Is it Bi-directional or uniderectional? What are some examples of control signals

Answer 33

* Used to send control signals * Manage and orchestrate the operation that take place inside a computer system * Control signals can be used to request communication between two units, acknowledge a communication request, specify the data that is being transferred via the other buses and synchronising the communication between the components using the clock pulses * It is bidirectional, this means that it has a two-way connection between the components that the control bus connects * Examples of control signals include: Memory read, which places data from a specific memory location onto the data bus, memory write, which stores the data from the data bus onto a specific memory location , Bus request, which signifies that a component needs to access a bus, Bus grant, which signifies that a component is informed that it can use the bus it requested access to, bus busy, which signifies that a bus is not available for use, interrupt request, which signifies that an error or exception has occurred that requires the attention of the processor and clock signals, which the is used to supply the components with clock pulses generated by the system clock

Question 34

Assembly Languages - Addressing Modes

Answer 34

* In machine code, there are different addressing modes * Address modes can be specified as part of the opcode of an instruction * The addressing mode specifies the way in which the operand will be interpreted * There are 4 types of addressing modes * One addressing mode is the direct addressing mode, where data to be used is located in main memory or a register, and the operand specifies the address of memory or register location * A second addressing mode is immediate Addressing mode, where the data to be used is the actual value of the operand. This is often denoted with a # in assembly language. * A third addressing mode is the Indirect addressing mode, where the data to be used is located in main memory, and the operand specifies the memory location that contains within it another memory location that contains the data. The data is therefore referenced indirectly. * A final addressing mode is the Indexed addressing mode, where one of the dedicated registers in the CPU is the index register. Indexed referencing makes use of this register to access an array with data in successive memory locations.

Question 35

Assembly Language - Assembly Language

Answer 35

• The OCR syllabus requires you to be able to use the Little Man Computer instruction set to write simple programs in assembly language • The operations available in the LMC instruction set are: ○ HLT, which has the machine code number of 000, this ends the program ○ ADD, which has the machine code number of 1, This adds the content at the address specified by the operand into the accumulator ○ SUB, which has the machine code number of 2, This subtracts the contents at the address specified by the operand from the accumulator ○ STA, which has the machine code number of 3, This takes the value from the accumulator and stores it at the address specified by the operand ○ LDA, which has the machine code number of 5, This loads the value at the address specified by the operand into the accumulator ○ BRA, which has the machine code number of 6, This branches to the address specified by the operand ○ BRZ, which has the machine code number of 7, This branches to the address specified by the operand if the value in the accumulator is 0 ○ BRP, which has the machine code number of 8, This branches to the address specified by the operand if the value in the accumulator is 0 or positive ○ INP, which has the machine code number of 901, This takes from INPUT area ○ OUT, which has the machine code number of 902, This displays in OUTPUT area ○ DAT, which is not an instruction but is used to indicate a location that contains data and an optional value for initialisation. • When using LMC, there is a limited number of instructions available for the programmer

Question 36

Factors affecting processor performance - Multiple cores

Answer 36

• Computers with more than one processing unit (core) are called multicore. • The names for different core uses are: ○ Dual-core, which has two processing units ○ Quad-core, which has four processing units ○ Hexa-core, which has six processing units ○ octo-core, which has eight processing units * generally, the more cores a computer has, the more instructions it can execute at the same time. * because of this, the more cores a computer has, the more efficiently a computer can perform when compared to a computer with less cores. * However, having a quad-core instead of a dual-core processor (both running at the same speed) does not mean that the amount instructions that can be processed in the same time frame will double. * This can be seen in more complex instructions, where more complex instructions carried out by a quad-core may take a longer time when compared to a simple instruction carried out by a dual core * when multiple instructions are processed in a core with multiple cores, the core can go through parallel processing, where a single core can process a single instruction at the same time.

Question 37

Factors affecting processor performance - Cache in detail

Answer 37

* A cache is a fast, relatively small capacity set of locations that sit close to the processor * A cache is used to store the instruction and data most frequently is used * When running programs, a computer system is constantly swapping data in and out of cache and RAM * When an instruction or set of instructions, is frequently used during an operation, it is costly for a processor to fetch these from RAM * To overcome this, cache memory is used to store the instructions that are likely to be called upon. As with RAM, cached memory is erased when power is removed. * The size of cache memory varies greatly between older and newer systems, where the greater the size of cache memory the more instructions can be queued and carried out. * Also, the faster the cache, the faster an instruction is fetched to the processor. Where cache is placed is also important, since the closer the cache is to the processors, the faster it transfer instructions and data faster.

Question 38

Factors affecting processor performance - Clock Speed

Answer 38

* Processors are measured in terms of clock speed. * The clock is an electronic oscillator that produces a signal to synchronise the operations of the processor. * In general terms, the greater the clock speed, the faster instructions are carried out. * Clock speed is usually measured in GHz, where a processor with a clock speed of 3.6GHz allows for 3.6 billion 'state changes' per second * state changes does not correspond to a single instruction, so 3.6GHz does not mean it carries out 3.6 billion instructions per second.

Question 39

Factors affecting processor performance - Instruction pipelining

Answer 39

* Pipelining is a technique used to improve processor performance * It is based on the same principle as an assembly line in a factory * pipelining is the process or breaking an instruction down into smaller subtasks that can be handled independently. * This allows that one large complex problem, like manufacturing a phone, can be split into lots of smaller problems. * Pipelining can be used in multiple areas, such as in the fetch decode execute cycle, to make them more efficient.

Question 40

Computer architecture

Answer 40

Computer architecture refers to the structure and organisation of a computer system . It specifies the components that make up a computer system and describes how these are interconnected, how they interact with each other, and how they are managed