This series covers areas of knowledge you will need in order to pass the A+ Certification exam, and assumes that you have access to a computer which you can disassemble and “play with” to help you with the activities. Topics are organized to loosely follow Mike Meyers’ All-in-One CompTIA A+ Certification Exam Guide for the 700 series, so consider this a hands-on study guide supplement. Read chapters 8, 9 and 10 for this post on the motherboard, plus the expansion bus and power supply.
The three hurdles which are important to remember when adding expansion cards to the motherboard are the physical connection, communication, and drivers. Expansion cards have their own expansion bus crystal which sets a standard card speed independent of the system crystal on the motherboard. The expansion bus crystal is always slower than the system crystal, which is compensated for with wait states and buffering.
System Resources are methods of communication between the CPU and expansion cards. These include I/O addressing, interrupt requests, DMA, and memory addressing. I/O addresses are either preset or established by the operating system during the boot process, and can be viewed in Device Manager. The DMA controller can send data requests across the EDB when the CPU is performing internal calculations, which allows access approximately 95% of the time.
When installing expansion cards, make sure they are Windows Logo’d for compability, handle them by the edges of the card only, employ proper anti-static precautions, and unplug the computer to avoid a power trickle. If the card is used and has been stored previously, clean the slot connectors with contact cleaning solution. Uninstall old drivers in Control Panel, then install the device, then install new drivers (with the exception of USB and Firewire, which may require the driver to be installed before the device). After installation, use Device Manager to verify the connection. A device which is missing, not recognized or suffering a driver problem will have a yellow circle with a black exclamation point. A disabled or damaged device will have a red X. A device whose system resources were manually configured will display an “i”.
A motherboard’s form factor determines the size of the case, power supply, and airflow. The chipset determines the type of CPU and the type and capacity of RAM the system can handle. When choosing a motherboard, first decide if you will build an AMD or Intel system, and select a motherboard that supports higher CPU speeds and more memory than you initially plan to install so that the system will be upgradeable. Decide on the form factor, and choose a matching case (slimline, destop, mini-tower, mid-tower, tower or cube).
When replacing a motherboard, first remove all expansion cards and devices which will impede access. Remove the standout screws, then remove the motherboard. Install the CPU, fan, heatsink and RAM on the new motherboard before installing it in the case to prevent flexing the board. Screw the motherboard into the case, then hook up the PSU. If you have one, use a POST card to test the system, or install the keyboard, video card, speakers and monitor, then test the system. Install all wires from the built-in ports on the front of the case via pin connections, which are polarized and must be installed in the correct orientation.
A dying motherboard has three types of symptoms. Catastrophic failure means the computer will not boot – this happens most often with manufacturer defects known as burn-in, or in case of ESD damage. Component failure is rare and can be diagnosed by “flaky” connections. Ethereal failures are typically random and the problem must be isolated through the process of elimination.
A circuit breaker opens if too much current is flowing through a wire that cannot handle the load. A ground wire provides a path for excess electrons to escape in case of an overflow. The power supply unit connects to a wall outlet with a standard IEC-320 connector, and typically has a switch to specify 115V US current or 230V European current. A surge protector, rated in joules, will prevent damage to the PSU or computer by regulating the current against occasional sags and spikes. An uninerruptible power supply, rated in watts and voltamps, can protect a computer against data loss due to power outages. When purchasing a UPS, calculate the total wattage of components in your machine and the amount of time you would need the UPS to run.
A PSU converts AC voltage to 3.3, 5.0 and 12.0 DC voltage. A standard unit is 150x140x86mm and connects to the motherboard using a 20-24pin P1 connector. Some units may also include 4, 6, or 8 pin connectors. Peripherals connect to the PSU with molex, mini, or SATA connectors. A computer with insufficient PSU wattage may not boot after a new component is installed – when purchasing a new one, 500W is a minimum recommendation. PSUs are typically 70% efficient, so calculate the computer’s needs then add at least 30%.
When installing a PSU, remember that ATX power supplies never truly turn off unless unplugged from the wall outlet. Some power supplies come with a 3-pin heat sensor, and you should always have at least one case fan installed, drawing air in from the bottom front of the case and blowing hot air out of the top rear. If a PSU fan does not spin and the computer won’t turn on, verify the electrical current with a multimeter. Remember that the PSU won’t turn on unless connected to the motherboard or an ATX tester, and keep a Class C Electrical fire extinguisher near your work station for emergencies.
- Expansion Bus = slots, wires and support chips that allow the addition of expansion cards to the motherboard
- PC/XT Bus = IBM’s original expansion slots; 8-bit, ran faster than the system crystal and was open source to allow manufacturers to work with it
- AT Bus = 16-bit slots with backward compatibility to 8-bit devices
- ISA Bus = Industry Standard Architecture; slow and required manual configuration, but made great strides toward physical connectivity standardization
- PCI Bus = Peripheral Component Interconnect; self-configuring (plug and play) and open source, provided burst-mode feature for easy data transfer and could be paired with ISA on a single motherboard
- AGP = Accelerated Graphics Port; PCI slot with a direct connection to northbridge for video cards; slot is typically brown
- PCI-X = PCI extended; 64-bit slot with backward compability, for power users and servers
- miniPCI = used in laptops, low power consumption and flat form factor
- PCIe = PCI express; serial connection which sends all data on a single wire (rather than one wire per bit) directly to the northbridge; paired input and output lanes (up to 32) at 2.5 to 5GBps
- I/O Addressing = method of communication between CPU and expansion cards in which each device is assigned at least 4 unique input/output addresses; to send a command, the CPU puts the address bus in I/O mode and all devices “listen” for their addresses and the command
- Interrupt Requests = expansion cards can communicate with the CPU using an INT wire; requests sent on the INT wire are called IRQs
- IOAPIC = input/output advanced programmable interrupt controller; intermediary between expansion cards and CPU, all device INT wires run to this chip on the Southbridge, which then communicates with the CPU
- DMA = direct memory access; devices with this feature can access RAM without CPU interference, using a DMA controller as the intermediary between device requests and delivery; PCI and PCIe cards do not support DMA
- Bus Mastering = modern devices are capable of monitoring the EDB and bypassing the DMA controller to access RAM directly
- Memory Addressing = devices with onboard RAM or ROM borrow memory addresses from the system RAM so that the CPU can access it
- HCL = hardware compatibility list; also known as Windows Logo’d Hardware List, available on the Microsoft website and displayed on packaging of devices and drivers that have passed Windows Hardware Quality Labs testing; Windows Vista 64-bit will not allow installation of unsigned drivers
- traces = wires soldered to motherboard which support buses, ports and power distribution
- AT = motherboard form factor used until the mid-90s characterized by its lack of external ports except for the keyboard
- LPX/NLX = motherboard form factors with slimline or low profiles; included riser cards (also known as daughter boards) in order to attach cards horizontally; did not allow for updates
- ATX = improvement over AT motherboard form factor including rear panel ports, better air flow due to change in PSU location; CPU and RAM placed closer to Northbridge for faster performance and easier access; soft power allows software to control power on/off rather than the case power button, prevents accidental shut down and provides constant 5V charge
- microATX = 9.6×9.6″ motherboard form factor with standard ports
- flexATX = 9×7.5″ motherboard form factor, requires a smaller PSU
- BTX = Balanced Technology Expanded; motherboard form factor optimized for cooling; comes in standard, micro and pico sizes; thermal unit sucks cool air in the front and ejects hot air from the back, rather than allowing it to circulate in the case
- Northbridge = intermediary between CPU and RAM or video card; requires heatsink and fan for cooling; on Intel products, may be referred to as MCH or memory controller hub
- Southbridge = intermediary between CPU and expansion cards and mass storage devices; does not require cooling; on Intel products, may be referred to as ICH or input/output controller hub
- Super I/O Chip = supports floppy drives, parallel ports, modems; works with but is not considered part of the chipset
- AMR and CMR = security for modems and networks, typically provided onboard; AMR stands for audio modem riser, CMR stands for communication and networking riser
- Voltage = pressure of electrons running through a wire; measured in volts (V)
- Current = amount of electrons moving past a given point in a wire; measured in amps (A)
- Wattage = volts x amps; amount of electricity required for a device to run
- Ohms = amount of resistance in a wire
- AC/DC = alternating current is provided by power companies; direct current is a continuous circuit in which electrons flow only in one direction – this is used by most electrical appliances and requires conversion
- IEC-320 = standard wall outlet wattage, diagrammed below; test for proper current using a multimeter, volt-ohm meter, or digital multimeter
- Molex = PSU connector that supplies 5 or 12V and includes four rounded chamfer notches for installation
- Mini = PSU connector that supplies 5 or 12V, for floppy drives only
- SATA = 15-pin PSU connector that supplies all voltages, has an L shape and is for use with hard drives
- ATX12V 1.3 = ATX power setting with 20-pin main connector, P4 12V 4-pin connector and AUX 6-pin 3.3V and 5V connectors
- EPS12V = nonATX24-pin main connector with AUX, P4 and 8-pin connectors; used for server environments; includes rails in which the 12V, 5V and 3.3V connectors each split into multiple wires so each device has its own supply
- ATX12V 2.0 = 24-pin main connector with backward compatibility; SATA support only, 8-pin CPU connector compatibile with P4, PCIe 6-pin connector
- TFX12V = low-profile power supply form factor
- SFX12V = flexATX power supply form factor
- CFX12V = L-shaped power supply form factor for BTX micro systems
- LFX12V = low-profile BTX power supply form factor
- Active PFC = active power factor correction; eliminates PSU-damaging harmonics
- Modular cables = power supply cables which can be left out of the system; helps keep the case looking neater
Open up your computer. Inspect the motherboard. Identify the various expansion cards and see how they connect to the motherboard and power supply unit.
Calculate the wattage requirement for your current system. What size PSU would you buy if you needed a replacement?
Create flash cards for the terminology covered in this chapter, then test yourself!
Other posts in the A+ Certification for Librarians series: