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What is a CPU?

It has a number of different components which enables it to carry out its task of executing instructions


What components are in the CPU?

Control Unit
Arithmetic Logic Unit (ALU)
Dedicated Registers


What does the control Unit do?

The CU controls and coordinates the activities of the CPU, directing the flow of data between the CPU and other devices


How does the Control Unit work?

It accepts the next instruction, decodes it into several sequential steps such as fetching addresses and data from memory, manages its execution and stores the resulting data back in memory or registers


What is a bus?

A bus is a set of parallel wires connecting two or more components of a computer.


What is the number of lines in a bus?

It typically consists of 8, 16, 32 or 64 lines


How do all the buses work?

When the CPU wishes to access a particular main memory location
1) It sends this address to memory on the address bus
2) The data in that location is then returned to the CPU on the data bus
3) Control signals are sent along the Control bus


What is a system bus?

The three bus, address, data and control bus are collectively known as the system bus.


What is a shared transmission medium?

Each bus is a shared transmission medium, so that only one device can transmit along a bus at any one time.


Which buses travel in both direction?

Data and control signals travel in both direction between the processor, memory and input output controllers


Which buses travel only one way

Addresses travel only one way along the address bus: the processor sends the address of an instruction, or of data to be stored or retrieved, to memory or to and input output controller


What are the three buses called?

1) Control bus
2) Data bus
3) Address bus


What is the purpose of a Control bus?

The purpose of the Control bus is to transmit command, timing and specific status information between system components


The Control bus is a _______ bus



What does the Control line do?

Control lines must be provided to ensure that access to and use of the data and address buses by the different components of the system does not lead to conflict


Control lines include:

Bus request
Bus grant
Memory write
Memory read
Interrupt request


What is bus request?

Indicates that a device is requesting the use of data bus


What is bus grant?

Indicates that the CPU has granted access to the data bus


What is memory write?

Caused data on the data bus to be written into the addressed location


What is memory read?

Causes data from the addressed location to be placed on the data bus


What Is interrupt request

Indicates that a device is requesting access to the CPU


What is clock (control lines)

Used to synchronise operations


What is the purpose of a data bus?

It’s provides a bi-directional path for moving data and instructions between system components. Typically has 8, 16, 32 or 64 separate lines


Memory is divided up internally into units called....



What is a word?

A word is a fixed size group of digits, typically 16, 32 or 64 bits, which is handled as a Unit by the processor, and different types of processor have different word sizes.


How does the address bus work?

Each word in memory has its own specific address. The address bus transmits the memory addresses of words that are used as operands in program instructions, so that the data can be retrieved and sent back to the processor. When an instruction has been performed and the result is to be stored at a particular memory location, it is transmitted via the data bus.


What does the ALU do?

Performs arithmetic and logical operations on the data.


Give an example of what the ALU does.

Performs instructions such as:
Shift Operation
Boolean logic operations


What is a Shift Operation?

Shifting bits to the left or right within a register


What is a Boolean logic operations?

Comparing two values and using operators such as AND, OR, NOT, XOR


What is a register?

Registers are special memory cells that operate at very high speeds.


Where do all arithmetic, logical or shift operations take place?

The registers


How many registers are in a CPU

Typically there are up to 16 general purpose registers in the CPU


What is an accumulator?

The accumulator takes the place of the general purpose registers. All the calculations take place in a single register called the accumulator.


List the special-purpose registers:

-Program Counter (PC)
-Current Instruction Register (CIR)
-Memory Address Register (MAR)
-Memory Data Register (MDR)


What does the program counter do?

Holds the address of the next instruction to be executed.


What does the Current Instruction Register (CIR) do?

Holds the current instruction being executed, divided into operand and opcode.


What does the Memory Address Register (MAR) do?

Holds the address of the memory location from which data or an instruction is to be fetched or to which data is to be written.


What does the Memory Data Register (MDR) do?

Is used to temporarily store the data read from or written to memory.


Describe the Fetch stage of the Fetch-Execute cycle?

1) The address of the next instruction is copied from the program counter (PC) to the memory address register (MDR).
2) The instruction held at that address is copied to the memory data register (MDR). simultaneously, the content of the PC is incremented so that it holds the address of the next instruction.
3) The contents of the MDR are copied to the current instruction register (CIR).


Describe the Decode stage of the Fetch-Execute cycle?

1) The instruction held int he CIR is decoded. The instruction is split into opcode and operand and the opcode is used to determine the type of instruction and what hardware to use to execute it. The operand holds either:
a) the address of the data to be used with the operation, which is then copied to the MAR, or
b) the actual data to be operated on, which will be copied to the MDR
c) the data to be operated on may be passed to the ALU/accumulator


Describe the Execute stage of the Fetch-Execute cycle?

The appropriate instruction/opcode is carried out on the operand.


What does Opcode mean?

Stands for Operation Code.


What does Operand mean?

The quality on which an operation is to be done.


What are the main factors affecting the CPU performance?

1) Clock Speed
2) Number of Cores
3) Amount of Cache memory


What is the system clock?

The system clock generates a series of signals, switching between 0 and 1 several million times per second and synchronising CPU operations.


What is Clock Speed?

The operating speed of a computer or its microprocessor


What is clock speed measured in?

Cycle per second = 1 Hertz(Hz)


How many processors does a Dual-core processor have?

Two processors linked together in the same integrated circuit.


What do cores do?

Each core are able to processes a different instruction at the same time with its own fetch-execute cycle.


Why do having multiple cores not always speed up software?

The software may not always be able to take full advantage of both processors.


What is Cache?

Cache is a small amount of expensive, very fast memory inside the CPU.


What does cache do?

When an instruction is fetched from main memory it is copied into cache so if it needed again soon after, it can be fetched from cache.


What is the advantage of cache?

It is mich quicker then going back to main memory.


What are the different levels of cache?

Level 1 - Extremely fast but small (2-64KB)
Level 2 - Fairly fast and medium-sized (256KB-2MB)


What is pipelining?

Technique used by some processors to improve performance. Without pipelining, the steps in the Fetch-Execute cycle take place on after the other. While the next instruction is being fetched, the ALU, the arithmetic part of the processor, is idle.


Where is pipelining most commonly used?

Microprocessors used in personal computers. Intel's Pentium chip uses pipelining to execute as many as six instructions simultaneously.


How is pipelining used?

The computer architecture allows the next instructions to be fetched at the same time as the processor is performing arithmetic or logic operations, holding them in a buffer close to the processor until the instruction can be performed.


What does the width of the address bus determine?

The maximum possible memory capacity of the system.


A system with a 32-bit address bus can address how much memory location?

2^32 memory locations giving an addressable memory space of 4GiB.


What does the data bus do?

The data bus transmits the data held in a word of memory, between processor components and memory.


What is the Stored Program Concept?

Defined as follows: machined instructions are fetched and executed serially by a processor that performs arithmetic and logical operations


In stored program concept where must the program be for it to be executed?

Main memory


How does the von Neumann machine work?

The same data bus is used to transfer both data and instructions. Similarly, a single address bus is used to transfer the addresses of data and instructions. The same word length is used for all memory, whether it holds data or instructions.


How does Harvard architecture work?

Physically separate memories for instructions and data.


Give an example of what Harvard architecture is used in.

Used extensively with embedded Digital Signal Processing (DSP) systems.


Give an example of a DSP application

Speech signal processing
Sonar and radar signal processing
Biomedical signal processing
Seismic data processing
Digital image processing


Give an example of: The two different memories can have different characteristics

In embedded systems instructions may be held in read-only memory while data memory requires read-write memory


What is an embedded system?

Special-Purpose computers built into devices often operating in real time


Give an example of where an embedded system would be used.

Navigation systems
Traffic lights
Aircraft flight control systems
Washing Machines


Which architecture is faster and why?

Harvard can be faster than von Neumann architecture because data and instructions can be fetched in parallel instead of competing for the same bus.


Give a comparison of von Neumann and Harvard architectures

Check book (pg.11)


What is a Contemporary processor architecture?

Modern high-performance CPU chips incorporate aspects of both von Neumann and Harvard architecture.


What does CISC stand for?

Complex Instruction Set Computers


How was CISC used?

A large instruction set is used to accomplish tasks in as few lines of assembly language as possible.


Give an advantage of CISC architecture

Compiler has very little work to do to translate a high-level language statement into machine code. Because the code is relatively short, very little RAM is required to store the instructions.


Give a disadvantage of CISC architecture

Many specialised instructions had to be built into the hardware even though only about 20% of them were used in the average program.


What does RISC stand for?

Reduced Instruction Set Computers


How does RISC architecture work?

Only simple instructions, each taking one clock cycle, can be executed.


Give a disadvantage of RISC

The ampler has to do more work to translate high-level code into machine code, and more RAM is required to store the machine code instructions.


Give an advantage of RISC

Because each instruction takes the same amount of time, i.e. one clock cycle, pipelining is possible, and the four instructions will execute at least as fast as the single CISC instruction.


Where is CISC still used

Microcontrollers and embedded systems


Which is mostly used as a processor design (CISC or RISC)



What is a Co-Processor System?

An extra processor used to supplement the functions of the primary processor (the CPU).


What can a Co-Processor be used for?

To perform floating point arithmetic,
Graphics processing,
Digital signal processing


Can a Co-Processor be used as a general-purpose processor.

It may not be a general-purpose processor with the ability to fetch its own instructions, do input and output operations and so on. It generally carries out only a limited range of functions.


What are Multi-Core CPUs

Multi-core CPUs are able to distribute workload across multiple CPU cores.


Give an advantage of a multi-core CPU

Achieves significantly higher perofmrance.
Can now perform parallel processing


What does GPU stand for?

Graphics Processing Unit


What is a GPU?

A specialised electronic circuit which is very efficient at manipulating computer graphics and image-processing.


What makes a GPU different to a CPU?

CPU has a few cores optimised for sequential serial processing, a GPU has a massively parallel architecture consisting of thousands of smaller, more efficient cores designed for handling multiple tasks simultaneously. Its highly parallel structure makes it suitable for tasks where processing of large blocks of visual data is done simultaneously.


Where would a GPU be on a personal computer?

On a graphics card, or embedded on the motherboard.


Give some generalised uses for a GPU.

Machine learning,
Oil exploration
Image processing
Financial transactions


A GPU is a form of?



List some input devices:

1) Barcode
2) Barcode readers
3) Digital Cameras
4) Radio Frequency Identification (RFID)


What is a barcode?

Used to store information which can be scanned by a barcode reader to find the information.


What are the two different types of barcodes?

1) Linear barcodes (1D)
2) 2D barcodes (QR codes)


Name the four types of barcode readers:

1) Pen-Type Readers
2) Laser Scanners
3) CDC Readers
4) Camera-Based Readers


How does a pen-type reader work?

A light source and a photo diode are placed next to each other in the tip of a pen. To read a barcode, the tip of the pen is dragged across all the bars at an even speed. The photo diode measured the intensity of the light reflected back from the light source and generates a waveform the tis used to measure the width of the bars and spaces in the barcode.


Give the advantages of a pen-type reader.

1) Simple design
2) Most durable
3) Tightly sealed against dust, dirty and other environmental hazards
4) Small and low weight makes it portable


Give the disadvantages of a pen-type reader

Applications are limited because they must come into direct contact with a barcode to read it.


How does a laser scanner work?

Same as pen-type except they use a laser beam as the light source


Give the advantages of laser scanners

They are reliable and economical for low-volume applications.


How do camera-based readers work?

Uses a camera and image processing techniques to decode a 1D or 2D bar code.


Give the advantages of a camera-based reader

Can read a barcode on any surface, printed or onscreen, and can also read a code that is damaged or poorly printed


What can camera based readers be used for:

1) Age verification - scanning driving licence
2) Couponing
3) Event ticketing


What are the two different sensors for digital cameras

CCD or CMOS (Complementary Metal Oxide Semiconductor)


How do Digital cameras work?

Uses a señor comprising millions of tiny light sensors arranged in a grid. The binary data from each sensor is recorded onto the camera's memory card so that the image can be reproduced using suitable software at a computer.


Which digital camera sensors is used in higher end cameras

CCD sensors tends to produce higher quality images.


Give an advantage of a CCD sensor in a digital camera

They are more reliable since the technology has been round for much longer.


Which sensor in a digital camera uses more power?

CCD higher quality images comes at the cost of power consumption, using up to 100 times that of a CMOS sensor.


Is an RDIF chip an input or output device?

The technology uses both input and output - an input device to read the signal from an RFID chip, and output to transmit a signal from an active tag.


Give the advantages of an RFID?

Can be read without line of sight and from up to 300 metres away.
Microchip transponder can be manufactured to less than 1mm in size but the antenna must be larger in order for it to communicate with a base unit.


How does a RFID chop work?

Consists of a small microchip transponder and an antenna.


What is an active tag in an RFID.

Active tags are physically larger as they include a battery to power the tag so that it actively transmit a signal for a reader to pick up.


Where are active tags (RFID) used?

These are used to track things likely to be read from further away, such as cars as they pass through a motorway toll booth or runners in a marathon as they pass mile markers.


What is an passive tag in an RFID

Passive tags are much cheaper to produce as they do not have a battery. They rely on the radio waves emitted from a reader up to a metre away to provide sufficient electromagnetic power to the card using its coiled antenna. Once energised, the transponder inside the RFID tag can send its data to the reader nearby.


Where are passive tags (RFID) used?

Most common in tagging items such as some groceries, much CDs, and for smart cards such as Transport for London's Oyster Card or a contactless bank card.


What are the different output devices?

1) Screens
2) Printers
3) Multimedia Projectors
4) Computer Speakers
5) Actuators


What are the two different types of screens?

1) LCD Monitors
2) Organic LED (OLED) screens.


What are the advantages of LCD monitors?

1) They reach their maximum brightness almost immediately.
2) The image is sharper with more realistic and vivd colours.
3) They produce a brighter light which leads to better picture definition.
4) Since LEDs are very small, screens can be much thinner in construction.
5) They last almost indefinitely which makes the screens much more reliable.
6) They consume very little power and therefore produce very little heat as well as reducing running costs.


How do LCD monitors work?

LCD monitors contain groups of red, green and blue diodes to form each pixel. The screen is typically back-lit using light-emitting diodes (LEDs).


What are the advantages of OLED screens?

1) When made of plastic rather than glass, they are theoretically flexible enough to bring onto clothing.
2) They are much thinner.
3) They are brighter and need to backlighting, so they consume less power, which translates into longer battery life in a portable device.
4) LCDs can be slow to refresh, OLEDs respond up to 200 times faster.
5) They produce truer colours though a much bigger viewing angle, unlike LCDs where the colours darken and disappear if you look from the side.


What can OLED screens be used for?

1) Tv and computer screens
2) MP3 and cell phone displays
They can be used wherever LCD screens are used for.


What is the disadvantage of OLEDs screens?

They do not last as long, tending to wear out around four times faster than LCDs.
They are very sensitive to water, which is a potential problem in a cellphone.


What are the different types of printers?

1) Laser Printers
2) InkJet Printers
3) Dot Matrix Printers
4) 3D Printers


What is a laser printer?

Laser printer offers high-quality, high-speed printing. Using powdered ink called toner.


Where are laser printer mostly used?

Used as home printer, in business and in professional printing services.


How do Inkjet printers work?

By spraying minute dots of ink onto papers to create an image.


Which printer is cheaper? (Inkjet or Laser)



What printer would be used to produce high quality photographic images?



What printer would be used to print lots of text?



How do Dot Matrix printer work?

The print head has a matrix of pins which strike the surface of the paper through an inked ribbon to form letters.


Where are Dot matrix printers used?

In damp or dirty environments.


What are the disadvantages of Dot matrix printers?

Poor Print Quality.


What can 3D printers be used for?

Car and aeroplane parts
Medical Equipment
Prosthetic limbs
Fashion accessories


What is an advantage of 3D printers?

They can be used for creating spare parts for obsolete equipment and produce prototypes of new products.


What are the advantage of Multimedia products?

1) In the old days 20 or more students would crowd around a desk trying to catch a glimpse of what the teacher was demonstrating on a 16" screen.
2) Copying down notes written on a chalkboard was hard.
3) Having an image to focus on while the teacher is explaining something can aid concentration.
4) Watching educational videos or even live webcams add interest to the lesson.


How are computer speakers used?

Giving verbal instructions in a sat-nav system, reading text from the screen for visually impaired people, giving warning beeps and notifications alerts.


What are actuators?

Are motors that are commonly used in conjunction with sensors to control a mechanism.


Give some examples of where actuators are used?

1) Opening a window or valve.
2) Starting or stopping a pump.
3) Turning a wheel.
4) Moving an aircraft aileron.
5) Controlling devices in a smart home.