A+ Core Hardware Service Technician

A+ Study Guide By CERTguide.com

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Breakdown

Exam Guide Study Notes

Resistors, capacitors, transistors, and diodes

Resistor  

• A resistor acts like a funnel to slow down the flow of current in a circuit 
• A resistor is an electrical component that limits or regulates the flow of electrical current in an electronic circuit. 
• Resistors can also be used to provide a specific voltage for an active device such as a transistor. 
• All other factors being equal, in a direct-current circuit, the current through a resistor is inversely proportional to its resistance and directly proportional to the voltage across it. 
• This is the well-known Ohm's Law 
• In alternating-current circuits, this rule also applies as long as the resistor does not contain inductance or capacitance 

Capacitor

• A capacitor is like a storage bin to hold a charge
• The PC has a few large capacitors that can literally kill you if you make contact with them, such as the capacitors in the monitor and in the power supply - That is why you should always exercise caution when opening up a CRT 
• A capacitor is a passive electronic component that stores energy in the form of an electrostatic field 
• In its simplest form, a capacitor consists of two conducting plates separated by an insulating material called the dielectric 
• The capacitance is directly proportional to the surface areas of the plates, and is inversely proportional to the separation between the plates 
• Capacitance also depends on the dielectric constant of the substance separating the plates 
• The standard unit of capacitance is the farad, abbreviated F  

Diode

• A diode is a one-way valve that allows the current to flow in only one direction 
• A diode is a specialized electronic component with two electrodes called the anode and the cathode 
• Most diodes are made with semiconductor materials such as silicon, germanium, or selenium 
• Some diodes are comprised of metal electrodes in a chamber evacuated or filled with a pure elemental gas at low pressure 
• Diodes can be used as rectifiers, signal limiters, voltage regulators, switch, signal modulators, signal mixers, signal demodulators, and oscillator 
• The fundamental property of a diode is its tendency to conduct electric current in only one direction 

Transistor  

• A transistor is a semiconductor that stores one binary value 
• The transistor, invented by three scientists at the Bell Laboratories in 1947, rapidly replaced the vacuum tube as an electronic signal regulator 
• A transistor regulates current or voltage flow and acts as a switch or gate for electronic signals 
• A transistor consists of three layers of a semiconductor material, each capable of carrying a current

ESD

•          Short for electrostatic discharge, the rapid discharge of static electricity from one conductor to another of a different potential
•          An electrostatic discharge can damage integrated circuits found in computer and communications equipment

• Most of the computer’s electronic components use from 3 to 5 volts of electricity 
• An ESD shock of 30 volts can destroy a computer circuit 
• An ESD shock you can feel, such as on a doorknob, has around 3,000 volts 
• An ESD shock you can see carries about 20,000 volts

Motherboard form factors

Many different form factors are available - some that are generally accepted in the industry, and some that are open to interpretation by manufacturers 

The exam blueprint for the A+ Core Hardware exam lists only the three most commonly used motherboard form factors: 

• AT: A motherboard patterned after the original IBM PC AT motherboard. 
• Baby AT: A smaller version of the AT forms factor motherboard. 
• ATX: Similar in size to the Baby AT, the ATX adds additional features and is the most commonly used form in today’s PCs.   The ATX motherboard allows for easier installation of full-length expansion cards and cables and is easier to cool off

Bus structures

• Address: The components on the motherboard pass memory addresses to one another over the address bus 
• Control: Used by the CPU to send out signals to coordinate and manage the activities of the motherboard components 
• Data: Because the primary job of the computer is to process data, logically the data must be transferred between peripherals, memory, and the CPU 
• Power: The power bus is the river of life for the motherboard’s components, providing each with the electrical power it needs to operate

Cache memory

Inside the processor - internal cache

• Also known as primary cache, internal cache is located inside the CPU chip
• Also called on the die

On the motherboard - external cache

• Also called secondary cache, external cache is located on the motherboard outside the CPU
• This is the cache referred to on PC specifications

Level 1 (L1) cache:

• Level 1 cache is often used interchangeably with internal cache and rightly so
• L1 cache is placed internally on the processor chip and is of course, the cache memory closest to the CPU

Level 2 (L2) cache:

• L2 cache is normally placed on the motherboard very close to the CPU; but because it is not inside the CPU, it is designated as the second level of cache
• Although L2 cache is commonly considered the same as external cache, L2 cache can also be included on the CPU, just a little behind L1 cache

ROM

• While not solely a BIOS chip, ROM chips are permanently loaded with instructions during their manufacturing processes
• The instructions written to a ROM chip, which cannot be changed under any circumstances, are called firmware

• A PROM is essentially a blank ROM chip that can be programmed with data or instructions
• Using a PROM burner (also called a PROM programmer), a special device used to write to the PROM; you can store any data you want
• The PROM burner induces high voltage (12 volts as compared to the 5 volts used for normal PROM operations) to load the data to the chip

• An EPROM is a variation of the original PROM with the added feature that the data can be erased so that the chip can be reprogrammed
• Unlike the PROM, you can reuse the EPROM instead of discarding it when its contents are no longer valid
• The EPROM has a small quartz crystal window on the top of the chip through which ultraviolet (UV) rays can access the chip’s circuitry

Electronically Erasable Programmable Read Only Memory (EEPROM):

• An EEPROM is the common BIOS chip on newer systems
• An EEPROM chip can be reprogrammed like the EPROM, but unlike the EPROM it doesn’t need to be removed from the motherboard
• An EEPROM can be updated through specialized software usually supplied by the BIOS or chip manufacturer from its Web site
• This process is known as flashing, which is why this chip is also commonly called flash ROM

DRAM

• This is the most common type of DRAM
• It’s common in most Pentium and later PCs, except those with memory buses over 75MHz

Fast Page Mode (FPM):

• This type of DRAM is occasionally called non-EDO RAM
• It’s generally compatible with motherboards with memory buses with speeds under 66MHz

Burst Extended Data Out (BEDO):

• This DRAM is EDO memory with pipelining technology added for faster access times
• BEDO allows much higher bus speeds than EDO

Synchronous DRAM (SDRAM):

• Like its SRAM, SDRAM is tied to the system clock and reads or writes memory in burst mode

Rambus DRAM (RDRAM):

• Rambus is a proprietary DRAM technology developed by Rambus, Inc
• Go to: www.rambus.com if you are not sure what RAMBUS is
• Has memory speeds of up to 3.2Gbps
• RDRAM comes on a module that is very similar to a DIMM, called a RIMM (Rambus Inline Memory Module)

Synchronous Link DRAM (SLDRAM):

• This is an enhanced version of SDRAM memory that uses a multiplexed bus to transfer data to and from the chips rather than fixed pin settings
• SLDRAM has transfer rates as high as 3GBps range
• This is an open technology

Memory Layout

Conventional memory 

• The first 640K of system memory
• Used by operating system kernels and standard DOS programs, device drivers, and TSRs

Upper memory area - UMA          

• The upper 384KB of the first megabyte of memory
• Located right above conventional memory
• Reserved for the system BIOS and device drivers and special uses such as ROM shadowing
• Also called expanded memory or reserved memory

High memory area - HMA

• The first 64K (less 16 bytes) of the second megabyte of memory
• Although it’s the first 64K of extended memory, it can be accessed in real mode

Extended memory 

• All memory above 1MB or any memory above the high memory area
• Used by Windows for programs and data running in protected mode

System Resources

Interrupt request (IRQ):

• A request that tells the CPU to interrupt what it’s doing and takes care of the special needs of the device sending the IRQ
• Devices are assigned IRQ numbers
• When you install a new device that requires services from the CPU, it is assigned an IRQ number, which enables the CPU to know which device is interrupting and requesting service – Hence the acronym IRQ
• On occasion, devices may share an IRQ, provided both devices do not attempt to interact with the CPU at the same time

Direct memory access (DMA):

• DMA channels allow certain devices to bypass the processor and access main memory directly
• DMA devices have the intelligence to handle their own data transfers to memory
• Some bus architectures allow more DMA channels than others, but two devices can’t share a DMA channel

Input/Output (I/O) address:

• This system resource is assigned to a device via its expansion slot
• The I/O address, also called an I/O port or hardware port, allows the CPU to send commands directly to the device by writing them to an assigned area in memory that the device checks frequently
• The I/O address is a one-way-only line that works like a reverse IRQ
• The CPU uses the I/O address to send a command to the device
• If the device responds, it uses the data bus or DMA channel to do so
• Only one device can be assigned to an I/O address

Bus mastering:

• Another feature attached to expansion slots and expansion cards that allows one device to interact directly with another is bus mastering
• Usually, the expansion card plugged into a slot has a bus master processor on the card that directs this activity
• Most modern motherboards, especially those with the PCI bus support bus mastering because it improves performance

Memory Addressing

IRQ's

DMA

Cards

• Provides a 16-bit data bus
• The ISA bus is characterized by adding an additional short slot to a slot on the 8-bit bus to create the 16-bit connector
• ISA added eight additional IRQs and doubled the number of DMA channels
• ISA expansion cards were designated to the appropriate IRQ or DMA numbers through jumpers and DIP switches
• The ISA architecture also separated the bus clock from the CPU clock to allow the slower data bus to operate at its own speeds
• ISA slots are found on x286, x386, x486, and some Pentium based PCs

• It has a 32-bit data bus
• Uses software setup
• Has more I/O addresses available, and ignores IRQs and DMA channels
• EISA uses only an 8 MHz bus clock to be backward compatible to ISA boards

• VLB was used first on 486 systems and grew out of the need for the data bus to run at the same clock speed as the CPU

• Introduced with the Pentium PC, PCI is a local bus architecture that supports either a 32- or 64-bit bus, which allows it to be used with both 486 and Pentium computers
• The PCI bus is also processor independent because of a special bridging circuit contained on PCI boards
• Its bus speed is 33 MHz, giving it much higher throughput than earlier cards
• The PCI architecture and expansion slot also supports ISA and EISA cards
• PCI cards are also Plug-and-Play, which means they automatically configure themselves to the appropriate IRQ, DMA, and I/O port addresses

Cards (Laptops)

Type I:

• Cards that are 3.3mm thick, are used for memory additions, and have a single row of connectors

Type II:

• Cards that are 5mm thick and used primarily to add modems or network interface cards (NIC’s) Type II cards have two rows of connectors

Type III:

• Cards that are up to 10.5mm thick Often used to add an external hard disk to a notebook computer Type III cards have four rows of connectors

RAID Levels

• Interleaves data across multiple drives
• This technology is fast
• Doesn’t include mirroring, redundancy, or any other protection against device failure
• RAID 0 is not fault tolerant

• Slower but offers redundancy
• Provides fault tolerance by completely duplicating data on two independent drives
• This provides a failover disk in the event that one of the mirrored disks should fail

• Provides fault tolerance by transferring data to and from three or more hard disk drives with data striped across the drives and the parity bits
• Used to reconstruct the data in the event of a drive failure, stored on a separate and dedicated drive

• Provides fault tolerance by employing essentially the same application as RAID 3
• RAID 5 stores the parity bits from two drives on a third drive to provide for data stripe error correction
• Most widely used

File Systems

• A table used by DOS and early releases of Windows 3.x to place and locate files on a disk
• It also tracks the pieces of fragmented files

• The 32-bit file system used in Windows for Workgroups and older releases of Windows 95
• Switches in at Protected mode boot
• VFAT serves as an interface between applications and the physical FAT
• Support long filenames – 255 LFN Support instead of 8.3

• The file system used in Windows 95 (OSR2) and Windows 98
• It supports larger disk capacities (up to two terabytes) and because it uses a smaller cluster size, it produces more efficient storage utilization
• Windows 2000 supports FAT32 with disk volumes of up to 32GB
• This is also very dependent on the actual size of the hard disk but it is generally 4k cluster size

• The file system supported by IBM’s OS/2 operating system
• It supports disk drives as large as 2TB and individual files as large as 2GB and 256-byte filenames
• HPFS coexists on a system with an existing FAT file system

• Introduced with the Windows NT operating system and supported under Windows 2000 as NTFS 5.0, which is not completely backward compatible
• Windows NT and 2000 also supports FAT32 and the legacy FAT16 file systems
• NTFS allows the ability to set permissions at the directory or individual file level

VIDEO

• Displays text on a monochrome monitor
• This adapter is still used for servers, process control, and monitoring systems where the display contains only text and a color display is not needed

• VGA is the standard for video adapters on Windows as well as several other operating systems
• The VGA standard supports up to 640 x 480 with 16 colors or lower resolutions with 256 colors

• Most of the video standards that followed VGA and support resolutions and color depths higher than those of the VGA standard are grouped under the SVGA standard
• The SVGA standard was developed by the Video Electronics Standards Association (VESA), which is made up of monitor, graphics card manufacturers, and other companies interested in video standards
• SVGA video cards support several resolutions, including 800 x 600, 1,024 x 768, 1,280 x 1,024, 1,600 x 1,200, and higher and up to 4 billion colors, although 16.7 million colors is more commonly used as the standard
• This is the best we have so far

Networking Topologies

Bus

Mesh

Star

Ring

PRINTERS

• These printers create characters by forming a group of hard-wire pins into the pattern of the letter, number, or special character and then striking the entire pin group through a ribbon, forming the character on paper

• Inkjet printers are probably the most popular printer type in use
• They produce a better-quality print but without the noise of the dot-matrix printer and at a lower price than a laser printer
• Inkjet printers produce an image by heating ink into steam and then jetting it out onto paper
• Most common for household locations

• These printers use a complex printing process to produce very high-quality documents
• Laser printers are becoming more common on the desktop, especially with prices continuing to decline
• Most common in a business environment, less likely to smudge unlike inkjet

Printing Cycle

• Before a new page is printed, any remnants from the previous page are cleaned off
• The drum is swept free of any toner with a rubber blade, and a fluorescent lamp removes any electrical charge remaining on the drum by neutralizing it
• Any toner removed in this step is not reused but is put into a used-toner compartment on the cartridge to be discarded

• The entire drum is uniformly charged to about 600V by the primary corona wire or the main corona located inside of the toner cartridge
• This charge conditions the drum for the next step

• The laser printer controller uses a laser beam and a series of mirrors to create the image of the page on the drum
• The laser beam is turned on and off in accordance with the image to be created on the drum
• At the spot where the laser’s light contacts the photosensitive drum, the charge is reduced to about 100V
• After the image has been transferred to the drum this way, the controller also starts the page sheet through the printer, stopping it at the registration rollers

• The developing roller, also located inside the toner cartridge, has a magnet inside of it that attracts the iron / polyester particles in the toner
• As the developing roller rotates by the drum, the toner is attracted to the areas of the drum that have been exposed by the laser, creating the print image on the drum

• The back of the paper sheet (the one that has been waiting patiently at the registration rollers) is given a positive charge that attracts the negatively charged toner from the drum onto the paper as it passes
• After this step, the paper has the image of the page on it, but the toner, which is held only by simple magnetism, is not yet burned to it

• The fusing rollers apply heat and pressure to the toner, which melts and presses it into the paper to create a permanent bond
• The fusing rollers are covered with Teflon and treated with a light silicon oil to keep the paper from sticking to them

Make sure you know the Printing Process well

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