Personal Computer System

Personal Computer System

1. Cases and Power Supplies

   • The computer case contains the framework to support the internal components of a computer while providing an enclosure for added protection. Computer cases are typically made of plastic, steel, or aluminum and are available in a variety of styles.
     • Computer cases are referred to in a number of ways: Computer chassis, Cabinet Tower Box ,Housing
       • Several factors must be considered when choosing a case: Size of the motherboard Number of external or internal drive locations, called bays Available space
   • The power supply must provide enough power for the components that are currently installed and allow for other components that may be added at a later time. If you choose a power supply that powers only the current components, you might need to replace the power supply when other components are upgraded.
     • Connectors Most connectors today are keyed. A keyed connector is designed to be inserted in only one orientation. Each power supply connector uses a different voltage, as shown in Figure 2. Different connectors are used to connect specific components to various ports on the motherboard.
       • A Molex keyed connector connects to optical drives, hard drives, or other devices that use older technology.
         • A Berg keyed connector connects to a floppy drive. A Berg connector is smaller than a Molex connector.
           • A SATA keyed connector connects to an optical drive or a hard drive. The SATA connector is wider and thinner than a Molex connector.
             • A 20-pin or 24-pin slotted connector connects to the motherboard. The 24-pin connector has two rows of 12 pins each, and the 20-pin connector has two rows of 10 pins each.
               • Older standard power supplies used two connectors called P8 and P9 to connect to the motherboard. P8 and P9 were unkeyed connectors. They could be installed backwards, potentially damaging the motherboard or power supply. The installation required that the connectors be lined up with the black wires together in the middle.
                 • A 4-pin to 8-pin auxiliary power connector has two rows of two to four pins and supplies power to all areas of the motherboard. The auxiliary power connector is the same shape as the main power connector but smaller. It can also power other devices within the computer.

2. Internal PC Components

   • The motherboard is the main printed circuit board and contains the buses, or electrical pathways, found in a computer. These buses allow data to travel between the various components that comprise a computer. Figure 1 shows a variety of motherboards. A motherboard is also known as the system board or the main board.
     • The motherboard accommodates the central processing unit (CPU), random access memory (RAM), expansion slots, heat sink and fan assembly, basic input/output system (BIOS) chip, chipset, and the circuitry that interconnects the motherboard components. Sockets, internal and external connectors, and various ports are also placed on the motherboard.
   • The flow of current between the electronic components generates heat. Computer components perform better when kept cool. If the heat is not removed, the computer may run slower. If too much heat builds up, computer components can be damaged. Increasing the air flow in the computer case allows more heat to be removed. A case fan installed in the computer case, as shown in Figure 1, makes the cooling process more efficient. In addition to a case fan, a heat sink draws heat away from the CPU core. A fan on top of the heat sink, as shown in Figure 2, moves the heat away from the CPU
   • Memory chips store data in the form of bytes. Bytes represent information such as letters, numbers, and symbols. A byte is a grouping of digital information in computing. A byte is most commonly a block of eight bits. Each bit is stored as either 0 or 1 in the memory chip. Read-only memory (ROM) chips are located on the motherboard and other circuit boards. ROM chips contain instructions that can be directly accessed by a CPU. Basic instructions for operation, such as booting the computer and loading the operating system, are stored in ROM. ROM chips retain their contents even when the computer is powered down. The contents cannot be erased or changed by normal means.
     • RAM is the temporary storage for data and programs that are being accessed by the CPU. RAM is volatile memory, which means that the contents are erased when the computer is powered off. The more RAM in a computer, the more capacity the computer has to hold and process large programs and files. More RAM also enhances system performance. The maximum amount of RAM that can be installed is limited by the motherboard.

3. External Ports and Cables

   • Input/output (I/O) ports on a computer connect peripheral devices, such as printers, scanners, and portable drives. The following ports and cables are commonly used:
     • Serial USB FireWire Parallel SCSI Network PS/2 Audio
       • Serial Ports and Cables A serial port can be either a DB-9, as shown in Figure 1, or a DB-25 male connector. Serial ports transmit one bit of data at a time. To connect a serial device, such as a modem or printer, you must use a serial cable. A serial cable has a maximum length of 50 ft (15.2 m).
         • Modem Ports and Cables In addition to the serial cable used to connect an external modem to a computer, a telephone cable connects the modem to a telephone outlet. This cable uses an RJ-11 connector, as shown in Figure 2. A traditional setup of an external modem using a serial cable and a telephone cable is shown in Figure 3.
           • Network Ports and Cables A network port, also known as an RJ-45 port, has 8 pins and connects a computer to a network. The connection speed depends on the type of network port. Standard Ethernet can transmit up to 10 Mb/s, Fast Ethernet can transmit up to 100 Mb/s, and Gigabit Ethernet can transmit up to 1000 Mb/s. The maximum length of network cable is 328 ft (100 m). A network connector is shown in Figure 8.
             • eSATA Data Cables The eSATA cable connects SATA devices to the eSATA interface using a 7-pin data cable. This cable does not supply any power to the SATA external disk. A separate power cable provides power to the disk.
               • SCSI Ports and Cables A SCSI port can transmit parallel data at rates in excess of 320 Mb/s and can support up to 15 devices. If a single SCSI device is connected to a SCSI port, the cable can be up to 80 ft long (24.4 m). If multiple SCSI devices are connected to a SCSI port, the cable can be up to 40 ft (12.2 m). A SCSI port on a computer can be a 25-pin, 50-pin, or 80-pin connector, as shown in Figure 7.

4. Input and Output Devices

   • An input device enters data or instructions into a computer. Here are some examples of input devices:
     • Mouse and keyboard Gamepad and joystick Digital camera and digital video camera Biometric authentication device Touch screen Digitizer Scanner
   • An output device presents information to the user from a computer. Here are some examples of output devices:
     • Monitors and projectors Printers and fax machines Speakers and headphones

5. Selecting PC Components

   • Before making any purchases or performing upgrades, first determine the customer’s needs. Ask the customer which devices will be connected to the computer both internally and externally. The computer case must be able to accommodate the size and shape of the power supply.
     • New motherboards often have new features or standards that may be incompatible with older components. When you select a replacement motherboard, make sure that it supports the CPU, RAM, video adapter, and other adapter cards. The socket and chipset on the motherboard must be compatible with the CPU. The motherboard must also accommodate the existing heat sink and fan assembly when reusing the CPU. Pay particular attention to the number and type of expansion slots. Make sure that they match the existing adapter cards and allow for new cards that will be used. The existing power supply must have connections that fit the new motherboard. Finally, the new motherboard must physically fit into the current computer case.
   • Before you buy a CPU, make sure that it is compatible with the existing motherboard. Manufacturers’ websites are a good resource to investigate the compatibility between CPUs and other devices. When upgrading the CPU, make sure the correct voltage is maintained. A Voltage Regulator Module (VRM) is integrated into the motherboard. You can configure the CPU voltage setting with jumpers, switches located on the motherboard, or settings in the BIOS.
     • The speed of a modern processor is measured in GHz. A maximum speed rating refers to the maximum speed at which a processor can function without errors. Two primary factors can limit the speed of a processor: The processor chip is a collection of transistors interconnected by wires. Transmitting data through the transistors and wires creates delays. As the transistors change state from on to off or off to on, a small amount of heat is generated. The amount of heat generated increases as the speed of the processor increases. When the processor becomes too hot, it begins to produce errors.

6. Specialized Computer Systems

   • You may need to design, build, and install computers for a customer that can accomplish a specific task. All computers can run programs, store data, and use I/O devices. A standard thick client is a traditional desktop computer that meets the recommended requirements for Windows and runs desktop applications.
     • Powerful processor - CAx software must make enormous amounts of calculations very quickly. You must meet the needs of the software when choosing a CPU.
       • High-end video card - Some CAx software is used to create 3D models. Realistic shading and texturing add to the complexity of the models, and a video card that can handle high resolutions and high detail is needed. Often, multiple monitors are desired or even required so that the user can work with code, 2D renderings, and 3D models all at the same time. Choose a video card that supports multiple monitors.
         • RAM - Because of the high amount of data processed by a CAx workstation, RAM is very important. The more RAM that is installed, the more data the processor can calculate before needing to read from slower storage, such as hard drives. Install as much memory as is supported by the motherboard and the operating system. The quantity and speed of the memory should exceed the minimums recommended by the CAx application.
     • In contrast, a specialized computer must support hardware and software that allows a user to perform tasks that a thick client cannot perform. One example of a specialized computer is a workstation used to run computer-aided design (CAD) or computer-aided manufacturing (CAM) software.