Computer Hardware and Components

UNIT 3: Hardware **Computers and their components** **Memory cache --** high speed memory external to processor which stores data which the processor will need again. **Random access memory (RAM) --** primary memory unit that can be written to and read from. **Read-only memory (ROM) --** primary...

UNIT 3: Hardware **Computers and their components** **Memory cache --** high speed memory external to processor which stores data which the processor will need again. **Random access memory (RAM) --** primary memory unit that can be written to and read from. **Read-only memory (ROM) --** primary memory unit that can only be read from. **Dynamic RAM (DRAM) --** type of RAM chip that needs to be constantly refreshed. **Static RAM (SRAM) --** type of RAM chip that uses flip-flops and does not need refreshing. **Refreshed --** requirement to charge a component to retain its electronic state. **Programmable ROM (PROM) --** type of ROM chip that can be programmed once. **Erasable PROM (EPROM) --** type of ROM that can be programmed more than once using ultraviolet (UV) light. **Hard disk drive (HDD) --** type of magnetic storage device that uses spinning disks. **Latency --** the lag in a system; for example, the time to find a track on a hard disk, which depends on the time taken for the disk to rotate around to its read-write head. **Fragmented --** storage of data in non-consecutive sectors; for example, due to editing and deletion of old data. **Removable hard disk drive --** portable hard disk drive that is external to the computer; it can be connected via a USB part when required; often used as a device to back up files and data. **Solid state drive (SSD) --** storage media with no moving parts that relies on movement of electrons. **Electronically erasable programmable read-only memory (EEPROM) --** read-only (ROM) chip that can be modified by the user, which can then be erased and written to repeatedly using pulsed voltages. **Flash memory --** a type of EEPROM, particularly suited to use in drives such as SSDs, memory cards and memory sticks. **Optical storage --** CDs, DVDs and Blu-rayTM discs that use laser light to read and write data. **Dual layering --** used in DVDs; uses two recording layers. **Birefringence --** a reading problem with DVDs caused by refraction of laser light into two beams. **Binder 3D printing --** 3D printing method that uses a two-stage pass; the first stage uses dry powder and the second stage uses a binding agent. **Direct 3D printing --** 3D printing technique where print head moves in the x, y and z directions. Layers of melted material are built up using nozzles like an inkjet printer. **Digital to analogue converter (DAC) --** needed to convert digital data into electric currents that can drive motors, actuators and relays, for example. **Analogue to digital converter (ADC) --** needed to convert analogue data (read from sensors, for example) into a form understood by a computer. **Organic LED (OLED) --** uses movement of electrons between cathode and anode to produce an on-screen image. It generates its own light so no back lighting required. **Screen resolution --** number of pixels in the horizontal and vertical directions on a television/computer screen. **Touch screen --** screen on which the touch of a finger or stylus allows selection or manipulation of a screen image; they usually use capacitive or resistive technology. **Capacitive --** type of touch screen technology based on glass layers forming a capacitor, where fingers touching the screen cause a change in the electric field. **Resistive --** type of touch screen technology. When a finger touches the screen, the glass layer touches the plastic layer, completing the circuit and causing a current to flow at that point. **Virtual reality headset --** apparatus worn on the head that covers the eyes like a pair of goggles. It gives the user the 'feeling of being there' by immersing them totally in the virtual reality experience. **Sensor --** input device that reads physical data from its surroundings. **[Types of memory and storage]** Computers require some form of memory and storage. - - - *Primary Memory* Primary memory is the part of computer memory which can be accessed directly from the CPU. - Primary memory allows the processor to access applications and services temporarily stored in memory Locations. - - - - - - - - - - - - - **Embedded systems:** Embedded systems involve installing microprocessors into devices to enable operations to be controlled in a more efficient way.  *Secondary Storage Devices* Secondary storage includes storage devices that are not directly accessible by the CPU. They are non-volatile devices which allow data to be stored as long as required by the user. This type of storage is much larger than primary memory, but data access time is considerably slower than RAM and ROM. Secondary storage devices fall into three categories: **magnetic, solid state and optical**. - - - - - - The benefits of SSDs over HDDs include: - - - - - - - - - - **[Input and output devices]** This section will consider laser printers, inkjet printers, 3D printers, speakers, microphones, screens and sensors. *Printers: laser, inkjet, 3D* - - - - - - Ink droplets are made using two main methods: - - When we use an inkjet printer to print the following process takes place: - There are different types of 3D printers, ranging from small to very large. 3D printing uses **additive manufacturing** (building up layers), unlike **subtractive manufacturing** (removing material to shape the object). Some common 3D printing methods: - - - *Speakers and Microphones* - To turn digital sound into actual sound: 1. 2. 3. If the sound is in a computer file, it has to go through a **Digital to Analog Converter (DAC)** to turn the digital data into an electric current that can power the loudspeaker. 1. 2. 3. 4. 5. The rate at which the DAC can translate the digital output into analogue voltages is known as the **sampling rate.** - The current produced can either be stored as sound (on, for example, a CD), amplified and sent to a loudspeaker, or sent to a computer for storage. Here's how a microphone works, broken down into steps: 1. 2. 3. 4. 5. *Screens* Screens are used to show the output from a computer. Modern screens use an LCD, backlit with **LEDs** or the newer **organic light emitting diode (OLED)** technology. - - **Touch screens** (which act as both input and output devices) also make use of LCD and OLED technology. They are particularly used in mobile phones and tablets. Two types of touch screen technologies : **capacitive and resistive**  *Virtual Headsets* - How VR headsets work: - - - - - - - *Sensors* - - - - Sensors are used in both monitoring and control applications. There is a subtle difference between how these two methods work. examples of monitoring and control applications of sensors:  **Logic gates and logic circuits** **Logic gates --** electronic circuits which rely on 'on/off' logic. The most common ones are NOT, AND, OR, NAND, NOR and XOR. **Logic circuit --** formed from a combination of logic gates and designed to carry out a particular task. The output from a logic circuit will be 0 or 1. **Truth table --** a method of checking the output from a logic circuit. They use all the possible binary input combinations depending on the number of inputs; for example, two inputs have 2^2^(4) possible binary combinations, three inputs will have 2^3^ (8) possible binary combinations, and so on. **Boolean algebra --** a form of algebra linked to logic circuits and based on TRUE and FALSE. **[Logic Gates]** Electronic circuits in computers, many memories and controlling devices are made up of thousands of **logic gates**. Logic gates take binary inputs and produce a **binary output**. Several logic gates combined together form a logic circuit and these circuits are designed to carry out a specific function. The checking of the output from a logic gate or logic circuit can be done using a **truth table.** **[The function of the 6 logic gates]** *NOT gate*  *AND gate* *OR gate* *NAND gate* *NOR gate*  *XOR gate*