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8/6/2019 Aplus notes2

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A+ Plus Notes:http://www.learnthat.com/courses/computer/apluscore

POST (Power On Self Test)The Power On Self Test, or POST, automatically runs every time you turn on your computer. It tests severalcomponents of your computer:The Processor - if the test fails on the CPU, the system stops, usually no error codeROMs - POST checks the BIOS ROMs, problems usually cause the system to stop with no error codeDMA Controller - if any problems, the system stopsInterrupt Controller - any problems and the system gives an audible error message of one long beep, then ashort beep, then the system stopsSystem timing chip - this chip provides timing signals for the bus and processor, this also gives a long beep anda short beep, then the system stopsVideo Card - if this fails, there is a long beep, then two short beeps, then the system haltsRAM - an error here generates a 201: Memory Error message on the screen, any error beginning with 2 is amemory 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 senseFloppy Drives - any problems cause a 601 - Floppy Disk error Other devices - POST checks the other ports and parts of the computer, beeps, then continues. It also checksthe 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:

Error Code Problem Description

1xx System Board problem

161 CMOS Battery Failure

164 Memory System Size error

2xx Memory related problem

3xx Keyboard problem

4xx Monochrome video problem

5xx Color video problems

6xx Floppy Disk problem17xx Hard disk problem

BIOSThe BIOS (Basic Input Output System) is the chip that contains low level software for configuring the system'scapabilities and communicating with the hardware. The BIOS is usually stored in the ROM and communicatesbetween 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 notupgradeable.The CMOS configuration program can usually be started using a key combination when you start up thecomputer.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.


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MemoryThe first type of memory is ROM. ROM is Read-Only Memory which is a form of non-volatile memory, meaningit keeps its information even when there is no power. It is also read only, so you cannot write to it. It contains thesetup 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 notpresent. 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 andstores 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 canbe reprogrammed.EEPROM, Electronically Erased PROM, can be erased using a special electrical charge. Chips can then bereprogrammed after erased. Most modern day BIOS's are stored in EEPROM.VRAM is video RAM and is used on video cards.Cache memory is memory used to cache CPU instructions. L1 is cache memory that is located on the CPU, L2is cache memory outside of the CPU.DIP, or Dual Inline Package, is an older type of RAM used mainly in older systems.

RAMRAM is broken up into DOS memory "sections". The first 640K of memory is Conventional Memory, which isused 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. Extendedmemory 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 KBpages (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 severalswitches, 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 thestarting 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 inCONFIG.SYS and DOS=UMB is there also.DOS=HIGH loads DOS into HMA.Device=HIMEM.SYS is the extended memory device driver.A Parity Error indicates a problem with RAM. Parity is a simple form of error checking and is used to checkRAM.

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

COM1 and COM3 use IRQ4. COM2 and COM4 use IRQ3. Most PCs only have two external COM ports.Parallel PortsParallel ports are used for printers, scanners, and sometimes drives. It is a 25 pin female, "D" connector. Itsends and receives 8 bit of data at one time.External ports send data in an asynchronous fashion.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.VideoVideo is a HDA connector. It is a 15 pin female with 3 rows of pins. (VGA & SVGA)


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Expansion SlotsThe expansion bus allows the computer to be upgraded using different modules. Expansion buses are made upwith copper slots where a circuit board can plug into it. The motherboard contains a bus clock which controlshow 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 DMAChannels, 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-bitcards have an extra piece extending beyond the 8-bit card length. This bus has 16 interrupts and 8 DMAchannels. 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 busand 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-bitbus and it has more I/O addresses with no need for interrupts or DMAs. It also still uses the 8 MHz of the ISAcard 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 backwardscompatible 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 isalso processor independent, allowing it to be on Macintosh, PC, and RISC computers. PCI runs at 33 MHz andhas 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 laptopsand other small computers and in some digital cameras. PCMCIA come in three types, Type I, Type II, and TypeIII.Type I cards are 3.3 mm thick. Type II cards are the most common and are 5 mm thick. Type III are mainly usedfor hard disks and are 10.5 mm thick.Summary Below is a chart summarizing the different buses:

Bus Type Bus Size Speed (MHz)

8-bit 8-bit 4.77

ISA 16-bit 8 (10 in turbo mode)

MCA 16-bit or 32-bit 10

EISA 32-bit 8

VESA Local 32-bit Processor Speed

PCI 64-bit Processor Speed

PCMCIA Card 16-bit 33 MHz

Cables & ConnectorsSerial CablesSerial cables communicate between two devices with serial ports. 50 feet is the maximum length a serial cableshould be. A null modem cable is used to communicate between two devices (such as computers).SCSI 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 isadvantageous 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. SCSIuses IDs to specify the device, which are numbered from 0-7. Most SCSI host adapters have to be set to SCSIID 7. Most external SCSI devices use a Centronics 50 or male DB-25 Connectors.Network CablesPhone lines (some types of networks) use a jack which resembles a phone jack, a RJ-11 or RJ-12. Another typeof network cable, twisted pair, uses RJ-45 connectors. This connector resembles a flat phone jack.

IRQs


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

IRQ Device Address (Hex) Device

0 Timer 00-0F DMA Controller

1 Keyboard 20-21 Interrupt Controller

2 Wired to IRQ 9 40-43 Timer 3 COM 2 (COM 4) 1F0-1F8 Hard Disk Controller

4 COM 1 (COM 3) 200-20F Joystick Controller

5 Available (often LPT2, soundcards, or network cards) 238-23B Bus Mouse

6 Floppy Disk Controller 278-27F LPT2

7 LPT1 2E8-2EF COM4 Serial Port

8 Clock 2F8-2FF COM2 Serial Port

9 Wired to IRQ 2 300-30F Ethernet Card

10 Unused 330-33F MIDI Port

11 Unused 378-37F LPT1 Port12 Mouse Port 3E8-3EF COM3 Serial Port

13 Coprocessor 3F0-3F7 Floppy Disk Controller

14 Hard Disk Controller 3F8-3FF COM1 Serial Port

15 Unused

In most PCs, there are 8 DMA Channels. In most modern PCs, DMA shouldn't be used, it just slows it down, butolder 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: The Processor The processor, or CPU (Central Processing Unit) controls and directs all activities in the computer. The CPUcontains millions of transistors. The CPU is measured by its clock speed in MHz. One megahertz is one millioncycles 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 mathcoprocessor, 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 upinto 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 toconnect with other devices, such as expansion cards and slots. The data bus is used to send and receive data.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 8088 chip has a 8-bit data bus and a 20-bit address bus.The 80286 chip has a 16-bit data bus and a 24-bit address bus.The 80386SX uses the 80387SX as its coprocessor and has a 32-bit data bus and a 24-bit address bus.The 80386DX has a 32-bit data bus and a 32-bit address bus.The 80486SX uses the 80487SX as its coprocessor and has a 32-bit data bus and address bus.The 80486DX has a 32-bit data and address bus.The 486DX2 has a 32-bit data and adress bus.The 486DX4 has a 32-bit data and address bus.The Pentium has a 32-bit data and address bus.The Pentium Pro has a 64-bit data bus and a 32-bit address bus.The Pentium Pro II has a 64-bit data and address bus.


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

The following tables summarize the processor chips and their characteristics:CPU Data Bus (bits) Address Bus (bits) Speed (MHz) Transistors

8088 8 20 4.77 29,000

80286 16 24 8-12 134,00080386SX 32 24 16-20 275,000

80386DX 32 32 16-33 275,000

80486SX 32 32 16-33 1.185 Million

80486DX 32 32 25-50 1.2 Million

486DX2 32 32 33-66 2 Million

486DX4 32 32 75-100 2.5 Million

Pentium 32 32 60-166 3.3 Million

Pentium Pro 64 32 150-200 5.5 Million

Pentium Pro II 64 64 233-400 7.5 Million

CPUs are mounted in different sockets depending on the size of the chip. Also, 486 chips and newer usuallycontain heat sinks, with fans, which fit on top of the processor chip.

The CPU socket information is summarized in this table:Socket Voltage Pins Processors Upgrade

0 3.3 168 486DX 486DX2 / 486DX4

1 3.3 169 486DX, 486SX 486DX2 / 486DX4

2 3.3 238 486DX, 486SX, 486DX2 486DX2/4, Pentium

3 3.3 or 5 237 486DX, 486SX, 486DX2, 486DX4 486DX2 / 486DX4

4 5 273 60/66 MHz Pentium Pentium

5 3.3 320 Other Pentium Pentium

6 3.3 235 486DX4 Pentium

7 3.3 321 Other Pentium Pentium

8 3.3 387 Pentium Pro Pentium Pro

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

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