Toggit A+ Study Guide for the CompTIA A Plus Core Hardware and Operating Systems Exam

Serial communication is used for modems, mice, and general communication uses. Serial ports are either 25 pin male, "D" Connector, or a 9 pin male, "D" Connector. It sends and receives 1 bit of data at one time.

COM1 and COM3 use IRQ4. COM2 and COM4 use IRQ3. Most PCs only have two external COM ports.

Parallel ports are used for printers, scanners, and sometimes drives. It is a 25 pin female, "D" connector. It sends and receives 8 bit of data at one time.

Keyboards are either DIN-5 or PS/2. PS/2 is a smaller port and is often on newer computers.

Your mouse is either a 9 pin serial or a PS/2. Again, the PS/2 is smaller and round, while the 9 pin serial is a D-type connector.

Video is a HDA connector. It is a 15 pin female with 3 rows of pins. (VGA & SVGA)

Serial cables communicate between two devices with serial ports. 50 feet is the maximum length a serial cable should be. A null modem cable is used to communicate between two devices (such as computers).

SCSI cables communicate between a SCSI port and a SCSI device, or between two SCSI devices. SCSI (Small Computer Systems Interface) is standard on most Macintoshes and optional on most PCs. SCSI is advantageous over other ports because of its high speed data rate and its ability to support up to seven devices (eight devices including the controller card).

Hard drives, tape drives, optical drives, scanners, and CD-ROM drives can all use the SCSI interface. SCSI uses IDs to specify the device, which are numbered from 0-7. Most SCSI host adapters have to be set to SCSI ID 7. Most external SCSI devices use a Centronics 50 or male DB-25 Connectors.

Phone lines (some types of networks) use a jack which resembles a phone jack, a RJ-11 or RJ-12. Another type of network cable, twisted pair, uses RJ-45 connectors. This connector resembles a flat phone jack.

There are three main types of hard drives: IDE, EIDE, and SCSI. The factory does a low level format on the hard drive prior to sending it out which organizes the hard drive into tracks and sectors. It is possible for you to perform a low level format of a drive but highly not recommended.

Before the installation of an operating system, you have to partition and format (high level format). When you partition a drive, you setup different virtual drives on the PC. Hard drives can have 3 primary partitions and 1 extended partition. Extended partitions can have up to 23 logical partitions.

A typical IDE drive supports up to 528 megabytes of storage while an EIDE drive supports 2 gigabytes and larger partitions. Most of the newer PCs you will work with will have two hard drive controllers, each supporting two devices. When you install a second drive on one controller with an existing drive, the first drive needs to be set to be a Master drive and the second a Slave drive. This is normally done using jumper settings on the hard drives.

A SCSI Controller will let you expand beyond the limit of 4 drives by allowing you to have up to seven additional SCSI devices for the controller. There are three different types of SCSI, SCSI 1, SCSI 2, and SCSI 3, also referred to as Ultra SCSI. SCSI 1 supports up to 8 devices, 1 of them being the SCSI Card. SCSI 2, which is the most popular, supports up to 16 devices and it has a higher transfer speed. If the exam does not specify which SCSI type you are using, assume it is SCSI 1 and has a maximum of 8 devices.

The SCSI chain must have a terminator at both ends. The SCSI card often has a built in terminator, and a lot of present day SCSI devices also have a switchable termination on the drive or device. SCSI drives are also more expensive than EIDE drives, but have a higher access speed and you can have access to more devices.

CD-ROM was developed by Sony and Phillips. It has a capacity of 650 megabytes of information and is burned onto a CD-ROM using a laser light.

CDFS (Compact Disk File System) is the type of filing system CD-ROMs use to store information.

There are three main types of interfaces for Tape Backup devices: Quarter Inch Cartage (QIC), SCSI, and LPT (printer port).

Controllers control the flow of data from sending and receiving devices. They match the speed between the devices and convert data between different formats.

A DTE device is a computer or printer. A DCE is a device such as a modem. A terminal sends a Ready To Send signal when it transmits to a DCE device such as a modem. A modem must have the Carrier Present signal before it is able to receive. RS232 is the standard for serial communication.

As we learned in the previous lesson, there are several types of SCSI. Here, we will expand on that topic and show you all types of SCSI. This table shows the characteristics of the different types of SCSI:

Generally speaking, the controller should be set at ID number 7. The higher the setting, the higher the priority. Slower drives should be set with a higher ID so they can access the bus whenever they need to. Each device has to have a unique ID. In general, the bootable hard drive is set to an ID of 0 and the CD-ROM to an ID of 3. This is not a requirement, just a suggestion.

PCMCIA (Personal Computer Memory Card International Association) was originally designed to help expand memory in handheld computers. It is a 16-bit bus interface type. PCMCIA is often referred to as PC Cards and supports many different types of devices including modems, Ethernet interfaces, and hard disks.

There are three types of PC Cards, Type I, Type II, and Type III. Type I cards are 3.3 mm thick. Type II cards are 5 mm thick and are mostly used for modems and Ethernet cards. This is the most common type of PC Card in today's systems. Type III cards are 10.5 mm thick and most often are hard disk cards.

PCMCIA cards use very little power and can be hot swapped - interchanged without rebooting your computer.

The computer power supply provides the power for all of the internal components to function. The power supply converts 110 volt AC into four voltages, +5 volts DC, -5 volts DC, +12 volts DC, and -12 volts DC (ground).

To remove a power supply and replace it, first, shut off the power and unplug the computer. Open the case.

Disconnect the power supply connectors from the internal components and motherboard.

Remove the mounting hardware from the power supply and the case. Remove the power supply.

The BIOS (Basic Input Output System) is the chip that contains low level software for configuring the system's capabilities and communicating with the hardware. The BIOS is usually stored in the ROM and communicates between the software and the hardware so less conflicts present themselves.

Since the BIOS contains the low level software controlling the computer, you may need to replace it in earlier PCs if you have to upgrade the hard drive.

Typical BIOS options include automatic detection of IDE drives, Option to enable/disable the processor/cache, Plug 'N' Play technology, and password protection.

The BIOS writes it configurations to the CMOS (Complementary Metal-Oxide Semiconductor). The CMOS is powered by a small battery so it can retain the settings after the power is turned off. the CMOS is usually not upgradeable.

The CMOS configuration program can usually be started using a key combination when you start up the computer.

When you enter the CMOS configuration program, you can usually change the hard disk type, display type, floppy disk type, boot sequence, serial & parallel configurations, date & time, password, and power management.

The expansion bus allows the computer to be upgraded using different modules. Expansion buses are made up with copper slots where a circuit board can plug into it. The motherboard contains a bus clock which controls how fast information flows to the expansion boards and back.

The 8-bit expansion bus operates at a maximum of 4.77 MHz (approximately 5), has eight interrupts, four DMA Channels, and one large 62 slot card.

The ISA (Industry Standard Architecture) bus is a 16-bit bus with a card slightly larger than the 8-bit. The 16-bit cards have an extra piece extending beyond the 8-bit card length. This bus has 16 interrupts and 8 DMA channels. ISA also runs at 8 MHz. ISA buses are also backwards compatible, allowing an 8-bit card to fit into it.

The MCA (Micro Channel Architecture) bus was a proprietary bus designed by IBM. It is a 16-bit or 32-bit bus and it's clock speed is 10 MHz. It also offered software configuration instead of dip switches and jumper settings.

EISA (Extended ISA) bus borrowed a lot of features from the MCA bus and expanded on them. It has a 32-bit bus and it has more I/O addresses with no need for interrupts or DMAs. It also still uses the 8 MHz of the ISA card bus to allow for backwards compatibility

The VESA Local Bus is a local bus type, meaning it is a bus that runs at the same speed as the processor. Typically, its used for video to take advantage of the high speed of transfer to the processor. It is backwards compatible with the ISA, but has an extra slot to make it 32-bits.

PCI (Peripheral Component Interconnect) Bus is the newest and most advantageous types of all of the buses. It supports both 32-bit and 64-bit data paths to be compatible with 486 and pentium class processors. PCI is also processor independent, allowing it to be on Macintosh, PC, and RISC computers. PCI runs at 33 MHz and has a maximum throughput of 256 megabytes per second.

PCMCIA (Personal Computer Memory Card Association) is the last type of bus. It is mainly used in laptops and other small computers and in some digital cameras. PCMCIA come in three types, Type I, Type II, and Type III.

Type I cards are 3.3 mm thick. Type II cards are the most common and are 5 mm thick. Type III are mainly used for hard disks and are 10.5 mm thick.

The processor, or CPU (Central Processing Unit) controls and directs all activities in the computer. The CPU contains millions of transistors. The CPU is measured by its clock speed in MHz. One megahertz is one million cycles per second. The first IBM PC CPU, the 8088, ran at 4.77 MHz, today's PCs can exceed 700 MHz.

With the chip is a math coprocessor which handles floating point calculations, like algebra and statistics. A math coprocessor, also called an FPU, handles most of the numeric operations.

Most processors have an internal cache which stores frequently used data and instructions. Cache is broken up into two classifications, L1 which is the internal cache and L2 which is the external cache.

Each processor have buses that go along with them. The external bus (system bus) allows the processor to connect with other devices, such as expansion cards and slots.

The address bus is used to describe memory address locations. Each CPU handles a different width of each of the different types of buses.

The 80386SX uses the 80387SX as its coprocessor and has a 32-bit data bus and a 24-bit address bus.

The 80486SX uses the 80487SX as its coprocessor and has a 32-bit data bus and address bus.

The MMX version of these chips is enhanced for multimedia applications and have several important characteristics. It has 57 instructions for manipulating video, graphic data, and audio. It also has more built-in cache on the chip.

CPUs are mounted in different sockets depending on the size of the chip. Also, 486 chips and newer usually contain heat sinks, with fans, which fit on top of the processor chip. The CPU socket information is summarized in this table:

There are two types of upgrade methods, ZIF (Zero Insertion Force) and LIF (Low Insertion Force) sockets. ZIF sockets have a mounting bar attached.

The first type of memory is ROM. ROM is Read-Only Memory which is a form of non-volatile memory, meaning it keeps its information even when there is no power. It is also read only, so you cannot write to it. It contains the setup program and POST (Power On Self Test) software.

RAM, or Random Access Memory, is a volatile type of memory which loses its information when power is not present. RAM is where your software and data is stored when your computer is on.

SRAM is an older type of memory, it stands for Static Random Access Memory. It is an older type of RAM and stores information using transistors.

DRAM, or Dynamic Random Access Information, stores information using capacitors.

PROM, Programmable Read Only Memory, this is a programmable type of ROM. It cannot be erased or changed once it is recorded.

EPROM, Erasable PROM, data can be erased using a UV light on a special window on the chip. This chip can be reprogrammed.

EEPROM, Electronically Erased PROM, can be erased using a special electrical charge. Chips can then be reprogrammed after erased. Most modern day BIOS's are stored in EEPROM.

Cache memory is memory used to cache CPU instructions. L1 is cache memory that is located on the CPU, L2 is cache memory outside of the CPU.

DIP, or Dual Inline Package, is an older type of RAM used mainly in older systems.

RAM is broken up into DOS memory "sections". The first 640K of memory is Conventional Memory, which is used to load DOS, run programs, and load drivers. DOS is loaded in the first 64K of memory.

Above 640K, but below 1024K is Upper Memory, also called Reserved Memory. 640KB - 768KB is Video Ram, 768KB - 960KB is for BIOS and RAM Buffers, and 960KB - 1024KB is Motherboard BIOS.

Above 1024K is Extended memory. High Memory Area (HMA) is the first 64K of extended memory. Extended memory is mainly used by Windows programs.

Expanded memory is sometimes used by DOS programs and is available up to 32 MB. It is swapped in 16 KB pages (addresses in pages of 16 KB).

In DOS, the MEM.EXE program allows you to determine how memory is being used by DOS. It has several switches, the important ones are highlighted here: /? the help switch, /C the classify switch - gives a report of how memory is used, /D the debug switch - details the first 640KB of memory, /F the free memory switch, shows all free memory blocks in the first 640KB of memory, /M (module) the module switch, shows the starting addresses of the data, program, and how much memory is allocated, and /P the pause switch, displays the output one page at a time.

To use upper memory, you need to make sure the upper memory device driver, EMM386.EXE is invoked in CONFIG.SYS and DOS=UMB is there also.

A Parity Error indicates a problem with RAM. Parity is a simple form of error checking and is used to check RAM

IRQs (Interrupt Request Lines) and DMAs (Direct Memory Addresses) are an important portion to study as they comprise several questions on the exam. The best method I found was to make flash cards with each IRQ and what it belongs to. Here is a chart of the common IRQs and what they belong to:

IRQ	Device
0	Timer
1	Keyboard
2	Wired to IRQ 9
3	COM 2 (COM 4)
4	COM 1 (COM 3)
5	Available (often LPT2, sound cards, or network cards)
6	Floppy Disk Controller
7	LPT1
8	Clock
9	Wired to IRQ 2
10	Unused
11	Unused
12	Mouse Port
13	Coprocessor
14	Hard Disk Controller
15	Unused

In most PCs, there are 8 DMA Channels. In most modern PCs, DMA shouldn't be used, it just slows it down, but older PCs may use DMA. Channels 4-7 are usually available, while Channel 0 is used to refresh DRAM, Channel 1 is used by a hard disk controller or sound card, and Channel 2 is usually the floppy disk controller.

Another important topic which should be memorized are the common I/O addresses, this table outlines those:

Address (Hex)	Device
00-0F	DMA Controller
20-21	Interrupt Controller
40-43	Timer
1F0-1F8	Hard Disk Controller
200-20F	Joystick Controller
238-23B	Bus Mouse
278-27F	LPT2
2E8-2EF	COM4 Serial Port
2F8-2FF	COM2 Serial Port
300-30F	Ethernet Card
330-33F	MIDI Port
378-37F	LPT1 Port
3E8-3EF	COM3 Serial Port
3F0-3F7	Floppy Disk Controller
3F8-3FF	COM1 Serial Port

The Power On Self Test, or POST, automatically runs every time you turn on your computer. It tests several components of your computer:

The Processor - if the test fails on the CPU, the system stops, usually no error code

ROMs - POST checks the BIOS ROMs, problems usually cause the system to stop with no error code

Interrupt Controller - any problems and the system gives an audible error message of one long beep, then a short beep, then the system stops

System timing chip - this chip provides timing signals for the bus and processor, this also gives a long beep and a short beep, then the system stops

Video Card - if this fails, there is a long beep, then two short beeps, then the system halts

RAM - an error here generates a 201: Memory Error message on the screen, any error beginning with 2 is a memory error

Keyboard - an error causes a 301 - Keyboard Failure error message on the screen, followed by a short beep, system may halt or may continue, some systems may ask you to press F1 to continue - which makes no sense

Other devices - POST checks the other ports and parts of the computer, beeps, then continues. It also checks the Master Boot Record (MBR) on the hard drive, if it cannot find the MBR, it will freeze and not continue loading, otherwise it hands control over to the MBR (or DOS Boot Record - DBR - if it is booting from a floppy)

Error codes - the following table summarizes the error codes and what they mean:

Electro-static Discharge (ESD) can cause damage to electronic components as you work on them. This will have several questions on the exam. ESD can be caused by static electricity your body picks up as you move, rub against your clothing, or can be picked up by things you touch.

While working on your computer, you should always wear an Electro static discharge wrist strap which grounds you. Also, it is recommended that you do not wear synthetic clothing, as your body rubs against synthetic clothing, it can create static electricity. This ESD Wrist Strap should not be worn while working on monitors though, it has stored voltage which could kill you.

When you store or ship electronic components, you should send them in antistatic bags. Antistatic bags do not conduct electricity, and can be reused.

As a computer service technician, it is very important for you to understand the basics of networking. Networks allows companies to share information, applications, printers, and other equipment.

Networks are broken down into two categories, Local Area Networks (LAN) and Wide Area Networks (WAN). Another type of network that may appear on the exam is the Metropolitan Area Network (MAN).

At the core of the network is the Server. The Server centralizes the control of resources, account management, and routes information to all of the workstations on the network.

Peer to Peer networks uses the computers in the network as both workstations and servers. This type of network does not have centralized authentication, but relies on each PC to interact with another.

Server based networks uses a computer as a server to have a central place for account management and resource management.

Networks are laid out in many different fashions. It is important to know the difference between the ways networks can be created.

The first way a network can be created is using the Bus Topology. This consists of a single cable to run to all of the workstations.

A third topology is the Ring type of network. A Ring connects each workstation to each other forming a ring through which messages pass to every workstation.

Most networks today are actually a Hybrid, or combination of one or more of the other types.

Networks communicate using Protocols. A protocol is simply a method for the network to communicate.

Ethernet is a network architecture. It has several different flavors, with the original Ethernet designed with 10base5. The "10" stands for 10 megabytes per second. Base is the Baseband communications is uses. The "5" stands for a maximum distance of 500 meters to communicate with. Original Ethernet used coaxial wiring, while newer versions use twisted-pair cabling.

There are several flavors of Ethernet, including 10Base2 (10 Mbps, 200 meters), 10BaseT (10 Mbps, 100 meters, twisted-pair), and 100BaseT (100 Mbps, 100 meter, twisted-pair).

Token-ring is the foundation for IEEE 802.5 specification networks. It uses a star, logical ring type of network. All of the workstations are cabled to a Multistation Access Unit, a MAU. The ring is created using this MAU.

There are four main types of network cabling: twisted-pair, coaxial, fiber optic, wireless.

Twisted-pair is the least expensive and most popular type of network cabling. It is several pairs of wires twisted around each other in an insulated covering. It is used a lot in 10BaseT networks.

Coaxial cabling consists of a copper wire surrounded by insulation and a foil shield. It is often used for 10Base2 cabling.

Fiber optic cabling is designed to transfer data at very high rates and over large distances. It carries a light pulse through a glass core at speeds of 100 Mbps - 1 Gbps.

Wireless networks consist of several different types of transmission medium. It can use microwave, radio, infrared light, or lasers.

Each workstation on the network has a Network Interface Card (NIC) and special software to allow it to communicate with the network.

Printers is a large part of the A+ Certification Core Exam and there are several sections that I guarantee will be on the exam. The most important part of the laser printer section is the order in which a laser printer operates, it will be at least one question on the exam.

Laser printers, also referred to as page printers, receive their information one page at a time and print using electrostatic charges, toner, and laser light.

The laser printer has several Field Replaceable Modules, including the Toner Cartridge, the Laser Scanning Assembly, High Voltage Power Supply, DC Power Supply, Paper Transport Assembly, Transfer Corona Assembly, Fusing Assembly, and the Formatter Board.

The EP Toner Cartridge holds the toner which is eventually what is printed onto the page. Toner is sensitive to the electrostatic charges. The Toner Cartridge also contains the print drum, charge corona wire, and the cleaning blade. The print drum is has a photosensitive material on it which holds static charge when it is not exposed to light. The charge corona wire charges the drum, while the cleaning blade does exactly what its name suggests, it cleans the used toner off the drum.

The Laser Scanning Assembly holds the laser which shines its light on certain parts of the printer drum. The electrical charge is reduced and the toner attaches itself to the drum where the laser has shined.

The High Voltage Power Supply takes 120 V AC and converts it to higher voltages for the charge corona wire and transfer corona wire. The DC Power Supply produces +5 Volt DC, -5 Volt DC, and +24 Volt DC from household current.

The paper transport assembly moves the paper through the printer. It is a series of motors and rollers to move the paper.

The Transfer Corona Assembly charges the paper with a positive charge as it moves through the printer. Once charged, it picks up the toner from the photosensitive drum.

The Fusing Assembly (also known as the fuser) applies pressure and heat to the paper to seal the toner particles to the paper. In the process of fusing, there is a halogen lamp which heats up to about 350 degrees F.

The Formatter Board is the circuit board that controls everything that is going on in the printer. It formats the information then tells the different modules to function together to get the printed page across.

The following is the order of processes that occur in a laser printer. It is an important part to memorize as there will be questions with this on it:

Conditioning - the EP drum is given a negative charge of about -600 Volts by the primary corona wire

Writing - A laser beam writes to the EP Drum, this laser causes portions of the drum to become almost positively charged

Developing - Toner is applied to the drum by the particles being transferred to the areas of positive charge

Transferring - The Transfer Corona wire charges the paper with a positive charge, the EP drum turns as the paper runs beneath it

Fusing - the paper runs through the Fusing Assembly which is heated to 350 degrees F, the toner is fused onto the paper

Dark spots on paper could indicate loose toner particles, run a few pages through to clear it up.

Always check the leading edge of paper when there is a paper jam, it can indicate what part of the printer is causing the jam.

The drum is photoconductive and loses its charge when light hits it. It is normally negatively charged during the print process.

Dot matrix printers are a form of impact printer. The printhead in a dot matrix printer is a series of pins which form numbers, letters, and graphics as it passes over the paper. In early dot matrix printers, 9-pin was a common size of printhead. This was called a draft quality printer. Later versions, such as the 24-pin printhead, print in near letter quality (NLQ) print mode.

During preventative maintenance, never lubricate the printhead of the printer. A tight ribbon could be the cause for flecks and smudges on the paper. Also, a missing or broken printhead pin could cause incomplete printing. If the print density is erratic, there can be a problem in the advancement of the printer ribbon.

Inkjet printers spray ink onto the page to form the letters and graphics. The inkjet printer has an ink cartridge which contains several chambers of ink. When the ink runs out, you must replace the ink cartridge. It is not recommended to refill ink cartridges

There are several major types of video, Monochrome, EGA/CGA (Enhanced Graphics Adapter, Color Graphics Adapter), VGA (Video Graphics Adapter), SuperVGA (Super VGA), and XGA (Extended Graphics Array). Each of these different types of video support differing numbers of colors and resolutions.

Monitors have two main characteristics, the dot pitch and the refresh rate. The dot pitch is described in millimeters (mm) and describes shortest distance between two dots of the same color. For example, a lot of present day monitors will have a 0.28 mm dot pitch, anything lower than that (such as 0.25 mm) is superior, anything larger (such as 0.31 mm) is less quality.

The second way to describe a monitor is in its refresh rate. The refresh rate (also know as vertical scan frequency) measures how many times per second the monitor is scanned. VGA has a standard refresh rate of 60 Hertz, or in other words, refreshes itself 60 times per second. The higher the number, the more times per second the monitor is being refreshed, which means less flicker is being perceived.