Section 1: Components of a computer Flashcards
What are the control unit’s functions?
Control Unit’s jobs:
- Guide data flow through different computer areas
- Regulates and controls processor timing
- Interprets instructions
- Controls sequential instruction execution
- Sends and receives control signals from other computer devices
What is the definition of a bus in computing?
A bus is a set of parallel wires connecting two or more components of a computer.
What are the 3 types of bus (along with the direction with which they move)?
The 3 types of bus are:
- The address bus, uni-directional
- The data bus, bi-directional
- The control bus, bi-directional
What does it mean if a bus is bi-directional?
If a bus is bi-directional then it can carry signals in both directions (as opposed to being uni-directional).
What is the job of the control bus?
The job of the control bus is to use control lines in order to make sure that access to and use of the data and address buses by different components does not lead to conflict.
Name 3 examples of control lines
Examples of control lines:
- Bus request
- Bus grant
- Memory write
- Memory read
- Interrupt request
- Clock
What does the data bus do?
The data bus provides a bi-directional path for moving data and instructions between components.
What is a memory address?
A memory address is an address in the memory for a specific word.
What does the Arithmetic Logic Unit do?
The ALU performs arithmetic and logical operations on the data.
What are registers?
Registers are special memory cells that operate at very high speed.
How many general purpose registers can typically be found in the CPU?
There are typically 16 general purpose registers in the CPU.
What does the Program Counter (PC) do?
The PC holds the address of the next instruction to be executed.
What does the Current Instruction Register (CIR) do?
The CIR holds the current instruction being executed, divided into operand and opcode.
What does the Memory Address Register (MAR) do?
The MAR holds the addresses 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?
The MDR temporarily stores the data read from or to be written to memory.
How does a processor access a particular main memory location using buses?
When the processor wishes to access a particular main memory location, it sends this address to memory on the address bus. The data in that location is then returned to the CPU on the data bus. Control signals are sent along the control bus.
What is the collective term for the 3 buses?
The collective term for the 3 buses is the system bus.
What is the accumulator?
The accumulator is a register that is used in specialised processors or used to represent general purpose registers in a simplified diagram.
What are the 3 stages of the fetch phase in the fetch-decode-execute cycle?
Fetch phase:
- The address of the next instruction is copied from the program counter to the memory address register
- The instruction held at that address is copied to the memory data register. Simultaneously, the content of the PC is incremented so that it holds the address of the next instruction.
- The contents of the MDR are copied to the current instruction register.
What happens during the decode phase in the fetch-decode-execute cycle?
Decode phase:
The instruction held in the CIR is decoded i.e. split into opcode and operand.
What is the opcode of an instruction?
The opcode of an instruction is the code that determines what type of instruction is to be executed and what hardware should be used when executing it (e.g. 0 means stop and 1 means add in a little man computer)
What is the operand of an instruction?
The operand of an instruction holds either:
- the address of the data to be used with the operation (which is then copied to the MAR), or
- the actual data to be operated on, which will be copied to the MDR (and may be passed through the ALU/accumulator)
What happens during the execute phase of the fetch-decode-execute cycle?
Execute phase:
The appropriate instruction/opcode is carried out on the operand.
What is meant by the word size of a computer?
The word size of a computer is the number of bits that can be processed by a computer’s CPU in one go (typically 32 or 64 bits)
What are the 3 main factors that affect processor performance?
The 3 main factors that affect processor performance are clock speed, number of cores and size or type of cache memory.
How is clock speed defined?
Clock speed is the speed at which a processor can cycle between 1s and 0s to complete instructions.
On what number do clock cycles begin on most computers?
On most computers, clock cycles begin at 0.
What is cache used for and why?
Cache is used to store the most frequently used data because it is much faster than main memory.
What is the typical range of capacity for level 1 cache?
The typical range of capacity for level 1 cache is 2-64KB.
What is the typical range of capacity for level 2 cache?
The typical range of capacity for level 2 cache is 256KB-2MB.
What is pipelining?
Pipelining is a technique used to make the most of the processor during the fetch-decode-execute cycle. It ensures that, while the processor is performing arithmetic and logic operations, the next instruction can already be fetched rather than allow the rest of the processor to be idle.
How does pipelining work?
Pipelining stops the fetch-decode-execute cycle from being sequential per instruction. Instead, while one instruction is being decoded and executed another can be fetched and ready for execution rather than allowing processor components to be idle.
How can pipelining be split up?
Pipelining can be split up into an arithmetic pipeline and an instruction pipeline. The instruction pipeline consists of the pipelining steps that are taken within the processor, while the arithmetic pipeline represents the parts of an arithmetic operation that can be broken down and overlapped as the tasks are being performed.
What is a word in computing?
A word is a group of bytes.
What does the width of the address bus determine?
The width of the address bus determines the maximum possible memory capacity of the system.
If a data bus is 32-bits, what is the maximum size of an integer that a word could hold?
If a data bus is 32-bits, the maximum size of an integer that a word could hold would be 2^32.
How is the stored program concept defined?
The stored program concept:
Machine code instructions are fetched and executed serially by a processor that performs arithmetic and logical operations.
What is the stored program concept often referred to?
The stored program concept is often referred to as the Von Neumann Machine.
What are the fundamental differences between Von Neumann architecture and Harvard architecture?
Differences between Von Neumann and Harvard architectures:
- In Von Neumann, instructions and data both share the same memory. In Harvard, they have different memories.
- Harvard architecture can allow for having larger or smaller capacity in either the instruction or data memory
Where is Von Neumann architecture typically used?
Von Neumann architecture is typically used in conventional processors in PCs, servers and embedded systems with only control functions.
Where is Harvard architecture typically used?
Harvard architecture is typically used in digital signalling processing and in embedded systems, mobile communication systems, audio, speech and image processing systems.
Why can Harvard architecture be faster than Von Neumann?
Harvard architecture can be faster than von Neumann because data and instructions can be fetched in parallel instead of competing for the same bus.
What is the contemporary processor architecture like?
Modern high-performance CPU chips take aspects of both aforementioned architectures. CPU cache memory can be divided into instruction and data cache (Harvard), while instructions and data may be stored together in main memory (von Neumann).
What is CISC?
CISC (Complex Instruction Set Computers) is a type of computer with a small set of complex instructions. Each instruction may complete a number of tasks.
What is are 2 advantages of CISC?
An advantage of CISC is that the compiler has very little work to do to translate a high-level language to machine code. Also, since the instruction set is small it takes up very little room in RAM.
What is a disadvantage of CISC?
A disadvantage of CISC is that the complex instructions must be built into the hardware, even though only about 20% of them are used in the average program.
What is RISC?
RISC (Reduced Instruction Set Computers) is a type of computer with a larger, simpler instruction set in which each instruction takes one clock cycle.
What is an advantage of RISC?
An advantage of RISC is that pipelining is possible because each instruction takes the same amount of time so they can be executed simultaneously. E.g. 4 RISC instructions should be quicker than 1 CISC instruction.
What are the main disadvantages of RISC?
The main disadvantages of RISC are that it takes a long time for the compiler to translate high-level code into machine code, and the instruction set takes up a lot of room in RAM.
Which is more prevalent in contemporary processor architecture out of RISC and CISC?
RISC is more common than CISC in contemporary processor architecture.
What is a co-processor?
A co-processor is an extra processor used to supplement the functions of the CPU. It will, most likely, not be a general-purpose processor that can fetch its own instructions or perform inputs and outputs.
What is a multi-core CPU?
A multi-core CPU is a CPU that can distribute workload across multiple CPU cores.
What are supercomputers often used for?
Supercomputers often use thousands of cores for things such as weather forecasting, running climate change models, processing big data or sequencing DNA.
What is the extent of improvement of having multiple cores dependent on?
The extent to which processing speed is improved by having multiple cores is dependent on the software’s ability to take advantage of the multi-tasking. This requires adjustments both to the operating system and to existing application software.
What is a Graphics Processing Unit (GPU)?
A GPU is a specialised electronic circuit, usually made up of thousands of cores, which is very efficient at manipulating computer graphs and image processing.
What are GPUs suited to and why?
GPUs are suited to tasks in which large amounts of data are processed simultaneously, due to the fact that they have a highly parallel structure.
What are examples of the uses of a GPU?
GPUs can be used for:
- Machine learning
- Image processing
- Financial transactions
- Oil exploration
How can a GPU be used alongside a CPU?
A GPU can be used alongside a CPU by offloading the compute-intensive parts of a program to the GPU while the remainder of the code runs on the CPU.
What can barcodes be used for?
Barcodes can be used for identification in thousands of applications from tracking parcels, shipping cartons, passenger luggage, blood, tissue and organ products around the world to the sale of items in shops and the recording of the details of people attending events.
What are the two types of barcodes?
The two types of barcode are linear (1-D) barcodes and 2-D barcodes such as QR codes.
Why are 2-D barcodes advantageous over 1-D barcodes?
2-D barcodes are advantageous over 1-D barcodes because they can hold more information.
What are the 4 different types of barcode reader?
The 4 different types of barcode reader:
- Pen-type readers
- Laser scanners
- CCD readers
- Camera-based readers
How is a pen-type reader structured?
In a pen-type reader, a light source and a photo diode are placed next to each other in the tip of a pen.
What is a photo diode?
A photo diode is a conductor which generates a potential difference when exposed to light.
How does a pen-type reader read barcodes?
In order to read a barcode, the tip-off of a pen-type reader is dragged across all the bars at an even speed. The photo diode measures the light intensity of the light reflected back form the light source and generates a waveform that is used to measure the widths of the bars and spaces in the barcode.
What is the main advantage of pen-type scanners?
Because of their simplicity, pen-type scanners are the most durable type of scanners and can be easily sealed against dirt, dust or other environmental hazards.
How do laser scanners work?
Laser scanners work in the same was as pen-type scanners, except they use a laser beam as a light source.
What are the advantages of laser scanners?
Laser scanners are reliable and economical for low-volume applications.
How do camera-based readers work?
Camera-based readers use a camera and image processing techniques to decode 1-D or 2-D barcodes.
What is the main advantage of camera-based readers?
The main advantage of camera-based readers is that they work on any surface, printed or onscreen, and can also work on badly damaged barcodes.
Where are camera-based readers often used?
Uses of camera-based readers:
- Age verification by scanning a driving licence
- Coupons
- Event ticketing
How does a digital camera work?
A digital camera uses a CCD or CMOS sensor comprising of 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.
What is the main advantage of a CCD sensor over a CMOS sensor?
The main advantage of a CCD sensor is that it produces higher quality images.
What is the main advantage of a CMOS sensor over a CCD sensor?
A CMOS sensor consumes around 100 times less power than a CCD sensor.
What is an RFID chip made up of?
An RFID chip is made up of a small microchip transponder and an antenna.
How do active tags differ from passive tags in size (and why)?
Active tags are physically larger than passive tags as they must contain a battery that powers the tag to allow it to transmit a signal.
How do active tags differ from passive tags in price (and why?)
Passive tags are much cheaper as they use radio waves emitted from a reader to transmit a signal rather than a battery.
How do passive tags work?
Passive tags 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 nearby reader.
What are some uses of active tags?
Uses of active tags:
- Tracking cars
- Tracking marathon runners
What are some users of passive tags?
Uses of passive tags:
- Tagging some groceries
- Contactless credit cards or travel cards (e.g. Oyster card)
How are LCD monitors structured?
LCD monitors contain groups of red, green and blue diodes to form each pixel. The screen is typically back-lit using LEDs.
What are the advantages of LCD monitors over older technology?
Advantages of LCD monitors:
- They reach their maximum brightness almost immediately
- They produce a sharper image with more vivid colours
- They produce a brighter light, leading to better definition
- LEDs are very small so they can be thinner in construction
- They last almost indefinitely making them more reliable
- They have lower running costs as they consume very little power and therefore produce very little heat
How do OLEDs differ from traditional LCD or LED screens?
OLED screens are plastic rather than glass making them flexible.
What are the advantages of OLEDs over LCDs?
Advantages of OLEDs over LCDs:
- OLEDs are theoretically flexible enough to print onto clothing
- OLEDs are much thinner
- OLEDs are brighter and need no backlighting so they consume less power leading to longer battery life in portable devices
- OLEDs are much quicker to respond (up to 200 times faster than LCDs)
- OLEDs produce truer colours through a much larger viewing angle
What are the advantages of laser printers?
Advantages of laser printers:
- Offer high-quality printing at high speeds
- Becoming increasingly cheap
How are laser printers limited?
Laser printers offer very little usage other than for text due to the quality of the print produced. They cannot quite produce photo-realistic prints.
How do inkjet printers produce an image?
Inkjet printers produce an image by spraying tiny dots of ink onto paper.
What are the advantages of inkjet printers?
Advantages of inkjet printers:
- Can produce excellent quality images
- Cheaper than laser printers
What are the disadvantages of inkjet printers?
Disadvantages of inkjet printers:
- Much slower than laser printers
- Ink cartridges have to be replaced quite frequently
How does a dot-matrix printer work?
In a dot-matrix printer, the print head has a matrix of pins which strike the surface of the paper through an inked ribbon to form letters.
What is multi-part stationery?
Multi-part stationery is printing paper stacked on top of each other (instead of being individual pieces of paper) that are used to make carbon copies.
What are the advantages of dot matrix printers?
Advantages of dot-matrix printers:
- Useful when multi-part stationery is required
- Can operate in damp or dirty environments
What are the disadvantages of dot matrix printers?
Disadvantages of dot-matrix printers:
- Noisy
- Slow
- Poor quality
What are 3-D printers typically used for?
3-D printers are typically used for creating spare parts for obsolete equipment and to produce prototypes of new products.
What are the benefits of a multimedia projector to students?
Advantages of a multimedia projector to students:
- Creates a big picture on a screen, making it easier for students to see and take notes from
- Having an image to focus on while a teacher is explaining a concept can aid concentration
- Watching educational videos adds interest to a lesson
What are the benefits of a multimedia projector to teachers?
Advantages of a multimedia projector to teachers:
- Can prepare one lesson to use for several classes without having to re-write things on the board – more consistence in lesson quality
- Can present text, graphics, audio and video on the screen; giving more freedom to best express and teach concepts
What are actuators?
Actuators are motors commonly used in conjunction with sensors to control a mechanism.
What are some examples of mechanisms controlled by actuators?
Examples of actuators:
- Opening a window or valve
- Turning a wheel
- Controlling devices in a “smart home”
What is the basic method by which all storage devices store data?
All storage devices use a technique which allows them to create and maintain a toggle state without power to represent either a 1 or a 0.
How does a hard disk work?
Firstly, iron particles on the hard disk are polarised to a north or south state, representing a 1 or a 0. The disk is divided into concentric circles called tracks, which is divided into sectors. The disk spins very quickly and a drive head moves across the disk to access different tracks and sectors, either reading data from them or writing data to them.
What does the drive head do when the disk is not in use (and why)?
When the disk in not in use, the drive head parks to one side in order to prevent damage from movement.
What are the 3 formats of optical disks?
The 3 formats of optical disks are read-only, recordable and rewritable.
How are optical disks written to?
An optical disk works by using a high-powered laser to burn sections of its surface, making a pit. The remaining spaces are called lands. A laser at a lower power is used to read the disk by shining light onto the surface and a sensor is used to measure the amount of light that is reflected back. Reflective and non-reflective areas are read as 1s and 0s.
What are the advantages of optical storage?
Advantages of optical storage:
- Very cheap to produce
- Easy to distribute
What is the main disadvantage of optical storage?
The main disadvantage of optical storage is that it can be easily corrupted or damaged by excessive sunlight or scratches.
In what capacity is data stored in pages?
Pages are typically 4KB each, grouped into blocks of around 512 KB.
What are the advantages of SSDs?
Advantages of SSDs:
- Consume far less power than hard disks, meaning battery life in laptops is extended and they stay cooler
- Less susceptible to damage than hard disks
- Silent in operation
- Lighter and more portable than traditional hard drives
- Faster access speed than hard disks as there are no moving parts
What are the disadvantages of SSDs?
Disadvantages of SSDs:
- Much more expensive than hard disks per GB
- Have a lower capacity than hard disks
What is virtual memory?
Virtual memory is an extension of memory provided by the hard drive that stores the least frequently used programs in the primary storage (RAM) when it gets full.
How are optical disks read from?
A laser at a relatively low power is used to read the disk by shining light onto the surface and a sensor is used to measure the amount of light that is reflected back. Lands and pits are read as 1s and 0s.
