The case of a desktop computer houses the internal components such as the power supply, motherboard, central processing unit (CPU), memory, disk drives, and assorted adapter cards. Show Cases are typically made of plastic, steel, or aluminum and provide the framework to support, protect, and cool the internal components. A device form factor refers to its physical design and look. Desktop computers are available in a variety of form factors including:
This list is not exhaustive, as many case manufacturers have their own naming conventions. These may include super tower, full tower, mid tower, mini tower, cube case, and more. Computer components tend to generate a lot of heat; therefore, computer cases contain fans that move air through the case. As the air passes warm components, it absorbs heat and then exits the case. This process keeps the computer components from overheating. Cases are also designed to protect against static electricity damage. The computer’s internal components are grounded via attachment to the case. 1.2.1.2 Power SuppliesElectricity from wall outlets is provided in alternating current (AC). However, all components inside a computer require direct current (DC) power. To obtain DC power, computers use a power supply, as shown here, to convert AC power into a lower voltage DC power. The following describes the various computer desktop power supply form factors that have evolved over time:
1.2.1.3 ConnectorsA power supply includes several different connectors, as shown in here. These connectors are used to power various internal components such as the motherboard and disk drives. The connectors are “keyed” which means that they are designed to be inserted in only one orientation. 1.2.1.4 Power Supply VoltageThe different connectors also provide different voltages. The most common voltages supplied are 3.3 volts, 5 volts, and 12 volts. The 3.3 volt and 5 volt supplies are typically used by digital circuits, while the 12 volt supply is used to run motors in disk drives and fans. Power supplies can also be single rail, dual rail, or multi rail. A rail is the printed circuit board (PCB) inside the power supply to which the external cables are connected. A single rail has all of the connectors connected to the same PCB while a multi rail PCB has separate PCBs for each connector. A computer can tolerate slight fluctuations in power, but a significant deviation can cause the power supply to fail. 1.2.1.5 Check Your Understanding - Cases and Power Supplies1.2.2 Motherboards1.2.2.1 MotherboardsThe motherboard, also known as the system board or the main board, is the backbone of the computer. As shown in the figure, a motherboard is a printed circuit board (PCB) that contains buses, or electrical pathways, that interconnect electronic components. These components may be soldered directly to the motherboard, or added using sockets, expansion slots, and ports. 1.2.2.2 Motherboard ComponentsThese are some connections on the motherboard where computer components can be added, as shown in the Figure 1:
Some additional important connectors are shown in Figure 2. 1.2.2.3 Motherboard ChipsetThe figure illustrates how a motherboard connects various components. Most chipsets consist of the following two types:
1.2.2.4 Motherboard Form FactorsThe form factor of motherboards pertains to the size and shape of the board. It also describes the physical layout of the different components and devices on the motherboard. There have been many variations of motherboards developed over the years. There are three common motherboard form factors:
The table in the figure highlights these and other form factor variations. 1.2.2.5 Check Your Understanding - Motherboards1.2.3 CPUs and Cooling Systems1.2.3.1 What is a CPU?The central processing unit (CPU) is responsible for interpreting and executing commands. It handles instructions from the computer’s other hardware, such as a keyboard, and software. The CPU interprets the instructions and outputs the information to the monitor or performs the requested tasks. The CPU is a small microchip that resides within a CPU package. The CPU package is often referred to as the CPU. CPU packages come in different form factors, each style requiring a particular socket on the motherboard. Common CPU manufacturers include Intel and AMD. The CPU socket is the connection between the motherboard and the processor. Modern CPU sockets and processor packages are built around the following architectures:
1.2.3.2 Cooling SystemsThe flow of current between electronic components generates heat. Computer components perform better when kept cool. If the heat is not removed, the computer may run more slowly. If too much heat builds up, the computer could crash, or components can be damaged. Therefore, it is imperative that computers be kept cool. Computers are kept cool using active and passive cooling solutions. Active solutions require power while passive solutions do not. Passive solutions for cooling usually involve reducing the speed at which a component is operating or adding heat sinks to computer chips. A case fan is considered as active cooling. The figure shows examples of passive and active cooling solutions. 1.2.3.3 Check Your Understanding - CPUs and Cooling Systems1.2.4 Memory1.2.4.1 Types of MemoryA computer might use different types of memory chips, as shown in the figure. However, all memory chips store data in the form of bytes. A byte is a grouping of digital information and represents information such as letters, numbers, and symbols. Specifically, a byte is a block of eight bits stored as either 0 or 1 in the memory chip. Read-Only MemoryAn essential computer chip is the read-only memory (ROM) chip. ROM chips are located on the motherboard and other circuit boards and contain instructions that can be directly accessed by a CPU. The instructions stored in ROM include basic operation instructions such as booting the computer and loading the operating system. ROM is nonvolatile which means that the contents are not erased when the computer is powered off. Random Access MemoryRAM is the temporary working storage for data and programs that are being accessed by the CPU. Unlike ROM, RAM is volatile memory, which means that the contents are erased every time the computer is powered off. Adding more RAM in a computer enhances the system performance. For instance, more RAM increases the memory capacity of the computer to hold and process programs and files. With less RAM, a computer must swap data between RAM and the much slower hard drive. The maximum amount of RAM that can be installed is limited by the motherboard. 1.2.4.2 Types of ROM1.2.4.3 Types of RAM1.2.4.4 Memory ModulesEarly computers had RAM installed on the motherboard as individual chips. The individual memory chips, called dual inline package (DIP) chips, were difficult to install and often became loose. To solve this problem, designers soldered the memory chips to a circuit board to create a memory module which would then be placed into a memory slot on the motherboard. The different types of memory modules are described in Figure 1. The speed of memory has a direct impact on how much data a processor can process in a given period of time. As processor speed increases, memory speed must also increase. Memory throughput has also been increased through multichannel technology. Standard RAM is single channel, meaning that all of the RAM slots are addressed at the same time. Dual channel RAM adds a second channel to be able to access a second module at the same time. Triple channel technology provides another channel so that three modules can be accessed at the same time. The fastest memory is typically static RAM (SRAM) which is cache memory for storing the most recently used data and instructions by the CPU. SRAM provides the processor with faster access to the data than retrieving it from the slower dynamic RAM (DRAM), or main memory. The three most common types of cache memory are described in Figure 2. Memory errors occur when the data is not stored correctly in the chips. The computer uses different methods to detect and correct data errors in memory. Different types of error checking methods are described in Figure 3. 1.2.4.5 Check Your Understanding - Memory1.2.5 Adapter Cards and Expansion Slots1.2.5.1 Adapter CardsAdapter cards increase the functionality of a computer by adding controllers for specific devices or by replacing malfunctioning ports. There are a variety of adapter cards available that are used to expand and customize the capability of a computer:
Figure 1 shows some of these adapter cards. It should be noted that some of these adapter cards can be integrated on the motherboard. Computers have expansion slots on the motherboard to install adapter cards. The type of adapter card connector must match the expansion slot. Refer to Figure 2 to learn about expansion slots. 1.2.5.2 Check Your Understanding - Adapter Cards and Expansion Slots1.2.6 Hard disk drives and SSDs1.2.6.1 Types of Storage DevicesA number of different types of devices are available for data storage on a PC, as shown in the figure. Data drives provide non-volatile storage of data, meaning that when the drive loses power, the data is retained and available the next time the drive is powered on. Some drives have fixed media, and other drives have removable media. Some offer the ability to read and write data, while others only allow data to be accessed, but not written. Data storage devices can be classified according to the media on which the data is stored; magnetic like HDD and tape drives, solid state, or optical. 1.2.6.2 Storage Device InterfacesInternal storage devices often connect to the motherboard using Serial AT Attachment (SATA) connections. The SATA standards define the way that data is transferred, the transfer rates, and physical characteristics of the cables and connectors. There are three main versions of the SATA standard: SATA 1, SATA 2, and SATA 3, as shown in the figure. The cables and connectors are the same, but the data transfer speeds are different. SATA 1 allows for a maximum data transfer rate of 1.5 Gb/s while SATA 2 can reach up to 3 Gb/s. SATA 3 is the fastest with speeds up to 6 Gb/s. Small Computer System Interface (SCSI) is another interface between motherboards and data storage devices. It is an older standard that originally used parallel, rather than serial, data transfers. A new version of SCSI known as Serially Attached SCSI (SAS) has been developed. SAS is a popular interface used for server storage. 1.2.6.3 Magnetic Media StorageOne type of storage represents binary values as magnetized or non-magnetized physical areas of magnetic media. Mechanical systems are used to position and read the media. The following are common types of magnetic media storage drives:
1.2.6.4 Semiconductor StorageSolid-state drives (SSD) store data as electrical charges in semiconductor flash memory. This makes SSDs much faster than magnetic HDDs. SSD storage capacity ranges from around 120 GBs to many TBs. SSDs have no moving parts, make no noise, are more energy efficient, and produce less heat than HDDs. Because SSDs have no moving parts to fail, they are considered to be more reliable than HDDs. SSDs come in three form factors:
These form factors are shown in Figure 1. Figure 2 shows the 2.5 inch and M.2 form factors in comparison to a 3.5 inch magnetic HDD. The Non-Volatile Memory Express (NVMe) specification was developed specifically to allow computers to take greater advantage of the features of SSDs by providing a standard interface between SSDs, the PCIe bus, and operating systems. NVMe allows compliant SSD drives to attach to the PCIe bus without requiring special drivers, in much the same way that USB flash drives can be used in multiple computers without requiring installation on each. Finally, Solid State Hybrid Drives (SSHDs) are a compromise between a magnetic HDD and an SSD. They are faster than an HDD but less expensive than an SSD. They combine a magnetic HDD with onboard flash memory serving as a non-volatile cache. The SSHD drive automatically caches data that is frequently accessed, which can speed up certain operations such as operating system start up. 1.2.6.5 Check Your Understanding - Data Storage Devices1.2.7 Optical Storage Devices1.2.7.1 Types of Optical Storage DevicesOptical drives are a type of removable media storage device that use lasers to read and write data on optical media. They were developed to overcome the storage capacity limitations of removable magnetic media such as floppy discs and magnetic storage cartridges. Figure 1 shows an internal optical drive. There are three types of optical drives:
CD, DVD, and BD media can be pre-recorded (read only), recordable (write once), or re-recordable (read and write multiple times). DVD and BD media can also be single layer (SL) or dual layer (DL). Dual layer media roughly doubles the capacity of a single disc. Figure 2 describes the various types of optical media and their approximate storage capacities. 1.2.7.2 Check Your Understanding - Types of Optical Media1.2.8 Ports, Cables, and Adaptors1.2.8.1 Video Ports and CablesA video port connects a monitor cable to a computer. Video ports and monitor cables transfer analog signals, digital signals, or both. Computers are digital devices that create digital signals. The digital signals are sent to the graphics card where they are transmitted through a cable to a display. 1.2.8.2 Other Ports and CablesInput/output (I/O) ports on a computer connect peripheral devices such as printers, scanners, and portable drives. In addition to the ports and interfaces previously discussed, a computer may also have other ports. 1.2.8.3 Adapters and ConvertersThere are many connection standards in use today. Many are interoperable but require specialized components. These components are called adapters and converters:
1.2.8.4 Check Your Understanding - Cables and Connectors1.2.9 Input Devices1.2.9.1 The Original Input DevicesInput devices allow the user to communicate with a computer. The images below are some of the first input devices. 1.2.9.2 New Input DevicesSome new input devices include touch screen, a stylus, a magnetic strip reader and a barcode scanner. 1.2.9.3 More New Input Devices1.2.9.4 Most Recent Input DevicesThe newest input devices include NFC devices and terminals, facial recognition scanners, fingerprint scanners, voice recognition scanners, and virtual reality headsets. 1.2.9.5 Check Your Understanding - Input Devices1.2.10 Output Devices1.2.10.1 What are Output Devices?An output device takes binary information (ones and zeroes) from the computer and converts it into a form that is easily understood by the user. Monitors and projectors are output devices that create visual and audio signals for the user (Figure 1). Virtual Reality (VR) headsets are another type of output device. Televisions may also be output devices. Printers are visual output devices that create hard copies of computer files. Speakers and headphones are output devices that produce only audio signals (Figure 2). Output devices make it possible for users to interact with computers. 1.2.10.2 Monitors and Projectors1.2.10.3 VR and AR HeadsetsVirtual Reality (VR) uses computer technology to create a simulated, three-dimensional environment. The user feels immersed in this ‘virtual world’ and manipulates it. A VR headset completely encases the upper portion of users’ faces, not allowing in any ambient light from their surroundings. Most VR experiences have three-dimensional images that seem life-sized to the user. VR experiences also track a user’s motions, and adjust the images on the user’s display accordingly. Augmented Reality (AR) uses similar technology but superimposes images and audio over the real world in real time. AR can provide users with immediate access to information about their real surroundings. An AR headset usually does not close off ambient light to users, allowing them to see their real life surroundings. Not all AR requires a headset. Some AR can simply be downloaded onto a smart phone. Pokemon GO is an early version of an AR game that uses a player’s smart phone to ‘see and capture’ virtual objects in the real world. Other AR devices are smart glasses. They weigh much less than the headsets and are often designed for a specific audience, such as cyclists. 1.2.10.4 PrintersPrinters are output devices that create hard copies of files. A hard copy might be a on a sheet of paper. It could also be a plastic form created from a 3D printer. The figure shows a variety of printer types. Today’s printers may be wired, wireless, or both. They use different technology to create the image you see. All printers require printing material (such as ink, toner, liquid plastic, etc.) and a method to place it accurately on the paper or extrude it into the desired shape. All printers have hardware that must be maintained. Most printers also have software, in the form of drivers that must be kept up to date. 1.2.10.5 Speakers and Headphones1.2.10.6 Check Your Understanding - Visual and Auditory Output Device CharacteristicsPage 2
Click Play in the figure to view an explanation of the items in a technician’s toolkit. Click here to read the transcript of this video. 1.3.1.2 Check Your Understanding - Technician’s Toolkit1.3.2 Computer Disassembly1.3.2.1 Video Demonstration - Computer DisassemblyClick Play in the figure to view a demonstration of the disassembly of a computer. Click here to read the transcript of this video. 1.3.2.2 Lab - Disassemble a ComputerIn this lab, you will disassemble a computer. Lab - Disassemble a Computer 5. 1.4 Summary | Next Section Previous Section |