Unit 3 - Hardware Flashcards
What is the CPU?
The Central Processing Unit is a microprocessor which consists of the control unit (CU), arithmetic and logic unit (ALU), registers, and buses. It is an integrated circuit which contains the ALU and CU to interpret and execute instructions and carry out arithmetic operations. It also contains the system clock and primary memory.
What is Von Neumann Architecture?
He introduced the idea of the stored program computer. It features the concept of a processing unit (CPU or processor) which could access the memory directly, as well as that computer memories could store programs (as well as data) which were made up of instructions which could be executed in sequential order.
What are the components of the typical CPU?
ALU - allows arithmetic (+, -) and logic (AND, OR) operations to be carried out. Allows multiplication and division using shifting operators.
CU - reads instruction from memory. Generates signals during the Fetch-Decode-Execute cycle to control all components of the computer.
Registers - can be general or special purpose. High speed areas of memory within a CPU used to store small amounts of data, address of next instruction to be executed, or current instruction being decoded. Includes current instruction register (CIR), accumulator (ACC), memory address register (MAR), memory data/buffer register (MDR), and program counter (PC).
System clock - produces timing signals on control bus to ensure all functions are synchronised. Changing clock speed can improve performance but there is a risk of overclocking (leading to overheating and system crashes).
System buses - transfer data and control signals throughout a computer. Use parallel transmission and bus width varies (bits used can be 8-64). Address bus (unidirectional) carries addresses throughout the system. Data bus (bidirectional) carries data to/from CPU/memory and to/from input/output. Control bus (bidirectional) carries signals from the CU to all computer components. The width of the data bus determines the word size (amount of data the CPU can contain) and the performance of the computer.
Memory - the random access memory (RAM) holds data, programs and parts of the operating system currently in use. All data being used in programs needs to be transmitted to the RAM. Memory is made up of an address (location of data and instructions) and its contents. All memory locations are unique. Primary memory also includes read-only memory (ROM) which cannot be altered and contains start-up routines for the computer.
What is the Fetch-Decode-Execute cycle?
Fetch - PC contains address of memory location of next instruction to be fetched from memory (MAR). Address is copied from PC to MAR (via address bus). Contents of memory location contained in MAR then copied into MDR. Contents of MDR then copied into CIR, and PC is incremented by one so next instruction can be processed.
Decode - instruction is now decoded so it can be interpreted.
Execute - CPU passes decoded instructions as set of control signals to appropriate computer components. This allows each instruction to be carried out in a logical sequence.
What is the purpose of a cache and cores?
Caches store frequently used instructions and data, speeding up CPU performance. Larger cache memory size means better CPU performance.
One core contains an ALU, CU and registers. More cores means better CPU performance. A quad core processor is a microprocessor with four independently operating cores that can read and execute CPU instructions.
What is an instruction set?
A set of operations that needed to be decoded in a sequence. Each operation contains an opcode and an operand;
- Opcode informs the CPU what operation needs to be done.
- Operand is the data which needs to be acted on or refers to registers in memory.
What are the main benefits and drawbacks of an embedded system?
Benefits:
- Small, easy to fit into devices.
- Relatively low cost to make.
- Usually dedicated to one task, making simple interfaces and often no need for an operating system.
- Consume very little power.
- Can be controlled remotely, e.g. using a mobile phone.
- Very fast reaction and reliability to changing input.
Drawbacks:
- Difficult to upgrade some devices to use new technology.
- Troubleshooting faults in the device is a specialist task.
- Can be accessed over the internet, so open to hackers, viruses, etc…
- Due to difficulty upgrading, devices are often thrown away rather than being repaired (wasteful).
- Can lead to environmental issues created by devices being discarded just for being out of date.
What is are 8 examples of input devices?
- Barcode readers - read series of black and white parallel lines varying in thickness, each representing digits 0-9.
- QR codes - another type of barcode made up of a matrix of dark and light squares, representing up to 7089 digits or 4296 characters.
- Digital cameras - produce digital images which can be easily transferred to a computer via USB or Bluetooth.
- Keyboards - can be physical (connected via USB or Bluetooth) or virtual (using touchscreen features).
- Microphones - a sensor which detects sound and convert them into electronic currents of varying amplitude, which can then be converted into digital data and stored in a computer memory.
- Optical mouse - used to move an on-screen cursor (using tiny cameras and a red LED light) which allows the user to carry out actions on the screen.
- Scanners - used to scan in information which is converted into an electronic format (e.g. text file format) to be stored on a computer memory.
- Touchscreens - common types include capacitive (relies on fingers touching the screen, changing electrostatic fields), infrared (relies on fingers to break the infrared beam so the CPU can calculate where the screen was touched), and resistive (relies on fingers applying force to a polymer surface, making contact with the glass surface underneath completing a circuit which allows current to flow at that point).
What are 6 examples of output devices?
- Actuators - mechanical or electromechanical device.
- Light projectors - digital light projector (DLP -> higher contrast ratios, reliability, longevity) and liquid crystal display (LCD -> sharper image, better colour saturation, more efficient).
- Printers - inkjet (spraying liquid ink droplets) and laser (dry solid ink melted on to paper).
- 3D printers - produces solid objects made from powdered resin, metal, paper or ceramics.
- LED and LCD screens - RGB and tiny liquid crystals.
- Speakers - produce sound from varying electric currents, using digital-analog converter (DAC) to store on computer.
What are the main types of sensors?
Sends signals to microprocessor via analog-digital converter (ADC);
Temperature, moisture, humidity, light, infrared (active and passive), pressure, acoustic/sound, gas, pH, magnetic field, accelerometer, proximity, flow rate, level.
What are the differences between RAM and ROM?
RAM = temporary memory device, ROM = permanent memory device.
RAM = volatile memory, ROM = non-volatile memory.
RAM = can be altered, ROM = cannot be altered.
RAM = used to store data currently in use, can be increased in size to improve computer speed, ROM = always used to store BIOS and other data needed for start-up.
