L1 TOPICA.pdf

PERSONAL COMPUTERS The components of a personal computer (PC) are divided between those that are designed to be handled by the user—peripheral devices—and those that would be damaged or dangerous if exposed. Peripheral devices typically perform the function of input (keyboard, mouse, microphone, and...

PERSONAL COMPUTERS The components of a personal computer (PC) are divided between those that are designed to be handled by the user—peripheral devices—and those that would be damaged or dangerous if exposed. Peripheral devices typically perform the function of input (keyboard, mouse, microphone, and camera), output (monitor and speakers), or external storage. The system case/chassis houses the internal components. These include the motherboard, central processing unit (CPU), system memory modules, adapter cards, fixed disks, and power supply unit. Most cases use a tower form factor that is designed to be oriented vertically and can be placed on a desk or on the floor. PCs can also be purchased as all-in-one units. All-in-one means that the internal components are contained within a case that is also a monitor. To perform PC maintenance, you must understand how to open a desktop computer's case. A tower case has a side cover that can be removed by sliding the panel from its housing. Cases might be secured by screws or retaining clips and might have anti-tamper security mechanisms. Always refer to the system documentation, and follow the recommended steps. The front panel provides access to the removable media drives, a power on/off switch, and light- emitting diodes (LEDs) to indicate drive operation. The front cover can be removed but may require the side panel to be removed first to access the screws or clips that secure it. The rear panel provides access to the power supply unit (PSU) sockets. The PSU has an integral fan exhaust. Care should be taken that it is not obstructed, as this will adversely affect cooling. There may be an additional case fan. Below the PSU, there is a cutout aligned with the motherboard's input/output (I/O) ports. These allow for the connection of peripheral devices. The spaces between the ports are covered by an I/O shield At the bottom of the rear panel there are cutout slots aligned with the position of adapter card slots to allow cables to be connected to any I/O ports on the cards. These slots should either be covered by an adapter card or a metal strip known as a blanking plate. The I/O shield and blanking plates are necessary to prevent gaps in the system case. Gaps create the following problems: Dust can enter the case and settle on the components, increasing the risk of damage through overheating. Components are more exposed to touching, increasing risks from electrostatic discharge (ESD). ESD means that a static charge on someone’s finger or on a tool is conducted into a computer chip. This can cause a temporary or permanent fault in the chip. Pins in the I/O shield connect the external metal parts of the ports to the metal case, which in turn is bonded to the PSU, which connects to the building’s ground system when plugged in. This provides a safe path for ESD to drain into, rather than flashing over into a chip. Components are more exposed to electromagnetic interference (EMI). EMI is energy from magnetic and electrical sources, such as motors or other electronic devices and radios, that can cause temporary or permanent faults. The PC’s case absorbs this energy, but gaps can reduce this protection. PERIPHERAL DEVICES An input/output (I/O) port allows a device to be connected to the PC via a peripheral cable. Some ports are designed for a particular type of device, such as a graphics port to connect a monitor. Other ports support a variety of device types. External ports are positioned at the rear or front of the PC through cutouts in the case. They can be provided on the motherboard or as an expansion card. Interfaces, Ports, and Connectors A hardware port is the external connection point for a particular type of bus interface. A bus allows the transfer of data to and from devices. The connector is the part of a peripheral cable that can be inserted into a port with the same shape or form factor. Each bus interface type might use multiple connector form factors. Most connectors and ports now use edge contacts and either have an asymmetric design called keying to prevent them from being inserted the wrong way around or are reversible. Binary Data Storage and Transfer Units When comparing bus interfaces, it is important to use appropriate units. Computers process binary data. Each binary digit or bit (b) can have the value one or zero. Storage is often measured in multiples of eight bits, referred to as a byte (B). A lowercase “b” unit refers to a bit, while uppercase means a byte. Transfer rates are expressed in units per second of the following multiples of bits and bytes: 1000—Kilobits (Kb/s or Kbps) and kilobytes (KB/s and KBps). 1000x1000—Megabits (Mb/s) or megabytes (MB/s). 1000x1000x1000—Gigabits (Gb/s) and gigabytes (GB/s). UNIVERSAL SERIAL BUS CABLES The Universal Serial Bus (USB) is the standard means of connecting most types of peripheral device to a computer. USB peripheral device functions are divided into classes, such as human interface (keyboards and mice), mass storage (disk drives), printer, audio device, and so on. A USB is managed by a host controller. Each host controller supports multiple ports attached to the same bus. In theory, there could be up to 127 connected devices per controller, but to overcome the limitations of sharing bandwidth, most PC motherboards provision multiple USB controllers, each of which has three or four ports.  USB port symbol. Variations on this basic icon identify supported features, such as higher transfer rates and power delivery USB Standards There have been several iterations of the USB standard. Each version introduces better data rates. A version update may also define new connector form factors and other improvements. The USB 2.0 HighSpeed standard specifies a data rate of 480 Mbps shared between all devices attached to the same host controller. The bus is half-duplex, meaning that each device can send or receive, but not at the same time. Iterations of USB 3.x introduced new connector form factors and upgraded transfer rates, each of which are full-duplex, so a device can send and receive simultaneously. USB 3.2 deprecated some of the older terms used to describe the supported transfer rate: Legacy Standard Speed Connectors Designation USB 3.2 Gen 1 SuperSpeed USB-A, USB-C, USB 5 Gbps USB 3.0 USB Micro USB 3.2 Gen 2x1 SuperSpeed USB-A, USB-C, USB USB 3.1 USB 10 Gbps Micro SuperSpeed+ 10 Gbps USB 3.2 Gen 2x2 SuperSpeed 2 x 10 USB USB-C Gbps 20 Gbps USB Connector Types The connector form factors specified in USB 2 are as follows: Type A—For connection to the host and some types of peripheral device. The connector and port are shaped like flat rectangles. The connector should be inserted with the USB symbol facing up. Type B—For connection to large devices such as printers. The connector and port are square, with a beveled top. Type B Mini—A smaller peripheral device connector. This type of connector was seen on early digital cameras but is no longer widely used. Type B Micro—An updated connector for smaller devices, such as smartphones and tablets. The micro connector is distinctively flatter than the older mini type of connector. A USB cable can feature Type A to Type A connectors or can convert from one type to another (Type A to Type B or Type A to Micro Type B, for instance). In USB 3, there are new versions of the Type A, Type B, and Type B Micro connectors with additional signaling pins and wires. USB 3 receptacles and connectors often have a blue connector tab or housing to distinguish them. USB 3 Type A connections are physically compatible with USB 1.1 and 2.0 connections, but the Type B/Type B Micro connections are not. So, for example, you could plug a USB 2 Type A cable into a USB 3 Type A port, but you could not plug a USB 3 Type B cable into a USB 2 Type B port. USB 3.1 defines the USB-C connector type. This compact form factor is intended to provide a single, consistent hardware interface for the standard. The connector is reversible, meaning it can be inserted either way up. The connector design is also more robust than the earlier miniB and microB types. USB-C can use the same type of connector at both ends, or you can obtain USB-C to USB Type A or Type B converter cables. Cable Length The maximum cable length for LowSpeed devices is 3 m, while for FullSpeed and HighSpeed the limit is 5 m. Vendors may provide longer cables, however. Although SuperSpeed-capable cables do not have an official maximum length, up to about 3 m is recommended. Power As well as a data signal, the bus can supply power to the connected device. Most USB Type A and Type C ports can be used to charge the battery in a connected device. Basic USB ports can supply up to about 4.5 watts, depending on the version. A power delivery (PD)–capable port can supply up to 100 watts, given suitable connectors and cabling. HDMI AND DISPLAYPORT VIDEO CABLES The USB interface supports many types of devices, but it has not traditionally been used for video. As video has high bandwidth demands, it is typically provisioned over a dedicated interface. Video cable bandwidth is determined by two main factors: The resolution of the image, measured in horizontal pixels by vertical pixels. For example, 1920x1200 is the typical format of high-definition (HD) video and 3840x2160 is typical of 4K video. The speed at which the image is redrawn, measured in hertz (Hz) or frames per second (fps). As examples, uncompressed HD video at 60 fps requires 4.5 Gbps, while 4K at 60 fps requires 8.91 Gbps. The frame rate in fps is used to describe the video source, while hertz is the refresh rate of the display device and video interface. To avoid display artifacts such as ghosting and tearing, the refresh rate should match the frame rate or be evenly divisible by it. For example, if the frame rate is 60 fps and the refresh rate is 120 Hz, the video should play smoothly. Computer displays are typically of the liquid crystal display (LCD) thin film transistor (TFT) type. Each pixel in a color LCD comprises cells with filters to generate the three additive primary colors red, green, and blue (RGB). Each pixel is addressed by a transistor to vary the intensity of each cell, therefore creating the gamut (range of colors) that the display can generate. The panel is illuminated by a light-emitting diode (LED) array or backlight. An LCD/TFT is often just referred to as a flat-panel display. They are also called LED displays after the backlight technology (older flat panels use fluorescent tube backlights). Premium flat-panel monitors are of the organic LED (OLED) type. This means that each pixel is its own light source. This allows for much better contrast and color fidelity. High-Definition Multimedia Interface The High-Definition Multimedia Interface (HDMI) is the most widely used video interface. It is ubiquitous on consumer electronics, such as televisions, games consoles, and Blu-ray players as well as on monitors designed for use with PCs. HDMI supports both video and audio, plus remote control and digital content protection (HDCP). Updates to the original HDMI specification have introduced support for high resolutions, such as 4K and 8K, and gaming features, such as the ability to vary the monitor refresh rate to match the frame rate of the video source. Support for audio is useful because most TVs and monitors have built-in speakers. The video card must have an audio chipset for this to work, however. There are full-size (Type A), mini (Type C), and micro (Type D) connectors, all of which are beveled to ensure correct orientation. HDMI cable is rated as either Standard (Category 1) or High Speed (Category 2). High Speed cable supports greater lengths and is required for v1.4 features, such as 4K and refresh rates over 60 Hz. HDMI versions 2.0 and 2.1 specify Premium High Speed (up to 18 Gbps) and Ultra High Speed (up to 48 Gbps) cable ratings. DisplayPort Interface HDMI was developed by consumer electronics companies and requires a royalty to use. DisplayPort was developed as a royalty-free standard by the Video Electronics Standards Association (VESA), which is an organization that represents PC graphics adapter and display technology companies. DisplayPort supports similar features to HDMI, such as 4K, audio, and content protection. There are full-size DP++ and MiniDP/mDP port and connector types, which are keyed against incorrect orientation. Bandwidth can be allocated in bonded lanes (up to four). The bitrate of each lane was originally 2.7 Gbps but is now (with version 2.0) up to 20 Gbps. One of the main advantages of DisplayPort over HDMI is support for daisy-chaining multiple monitors to the same video source. Using multiple monitors with HDMI requires one video card port for each monitor. THUNDERBOLT AND LIGHTNING CABLES Thunderbolt Interface Thunderbolt can be used as a display interface like DisplayPort or HDMI and as a general peripheral interface like USB. Thunderbolt versions 1 and 2 use the same physical interface as MiniDP and are compatible with DisplayPort so that a monitor with a DisplayPort port can be connected to a computer via a Thunderbolt port and a suitable adapter cable. Thunderbolt ports are distinguished from MiniDP by a lightning bolt/flash icon. Version 2 of the standard supports links of up to 20 Gbps. Like DisplayPort multiple monitors can be connected to a single port by daisy-chaining. Thunderbolt version 3 changes the physical interface to use the same port, connector, and cabling as USB-C. Converter cables are available to connect Thunderbolt 1 or 2 devices to Thunderbolt 3 ports. A USB device plugged into a Thunderbolt 3 port will function normally, but Thunderbolt devices will not work if connected to a USB port that is not Thunderbolt-enabled. Thunderbolt 3 supports up to 40 Gbps over a short, high-quality cable (up to 0.5 m/1.6 ft.). Not all USB-C ports support Thunderbolt 3. Look for the flash icon on the port or confirm using the system documentation. At the time of writing, converged USB 4 and Thunderbolt 4 standards have been developed, and products are starting to appear on the market. Lightning Interface Apple's iPhone and iPad mobile devices use a proprietary Lightning port and connector. The Lightning connector is reversible. The Lightning port is found only on Apple's mobile devices. To connect such a device to a PC, you need a suitable adapter cable, such as Lightning-to-USB A or Lightning-to-USB C. SATA HARD DRIVE CABLES As well as external cabling for peripheral devices, some types of internal components use cabling to attach to a motherboard port. Serial Advanced Technology Attachment Interface Serial Advanced Technology Attachment (SATA) is the standard means of connecting internal storage drives within a desktop PC. SATA uses cables of up to 1 m (39 in.) terminated with compact 7-pin connectors. Each SATA host adapter port supports a single device. The 7-pin data connector does not supply power. A separate 15-pin SATA power connector is used to connect the device to the PC’s power supply. The first commercially available SATA standard supported speeds of up to 150 MBps. This standard was quickly augmented by SATA revision 2 (300 MBps) and then SATA revision 3 (600 MBps). Molex Power Connectors Internal storage device data cables are unpowered. While the SATA power connector is the best option for new devices, legacy components connect to the power supply unit (PSU) via a Molex connector. A Molex connector is usually white or clear plastic and has 4 pins. The color coding of the wire insulation represents the DC voltage: red (5 VDC), yellow (12 VDC), and black (ground).  Some devices might have both SATA and Molex power connectors. External SATA There is also an external SATA (eSATA) standard for the attachment of peripheral drives, with a 2 m (78 in.) cable. You must use an eSATA cable to connect to an external eSATA port; you cannot use an internal SATA cable. eSATAp is a nonstandard powered port used by some vendors that is compatible with both USB and SATA (with an eSATAp cable). The USB interface dominates the external drive market, however.