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A+™ Essentials hardware Technologies

1. Some important acronyms: 

  • ISA is an acronym for Industry Standard Architecture, 
  • EISA is a acronym for Extended Industry Standard Architecture, 
  • PCI is an acronym for Peripheral Component Interconnect, and 
  • MCA stands for Micro Channel Architecture. 
  • CPU stands for Central Processing Unit. 
  • SCSI stands for Small Computers Systems Interface. It is pronounced as Skuzzy. 
  • DIMM stands for Dual-Inline Memory Module 
  • SIMM stands for Single-Inline Memory Module 
  • SRAM - Static random access memory - Uses transistors to store information 
  • DRAM - Dynamic random access memory - Need to be refreshed to retain data. 
  • ROM - Read only memory - Data in ROM can not be erased or changed 
  • PROM - Programmable ROM - Once programmed, data can't be erased or changed 
  • EPROM - Erasable PROM - Data can be erased by ultraviolet light and can be reprogrammed using a programmer. 
  • EEPROM - Electronically erasable PROM - Data can be erased electrically. Chip can then be reprogrammed. EEPROMs are frequently used to store BIOS. 

2. There are basically two important types of RAM: 

  1. DRAM - Dynamic RAM, and 
  2. SRAM - Static RAM. 

SRAM, being expensive, usually used for Cache memory. DRAM, being cheaper, is used for main memory.

3. PC Memory cards:

· A SIMM has a single row of 72 contact fingers, each making contact on both sides (Same pin number present on both sides of the card). An older version of SIMM card contain 30pins, and were used in 386 and some 486 machines.

· A DIMM (Dual-Inline Memory Module)has two rows of connecting fingers, one row on each side, and the total number of contacts are 168 contacts.

4. Monitor Connectors:

· If you are using a Monochrome / CGA/ EGA monitor, it is a digital monitor and will have a DB-9 Male connector that plugs into a digital adapter.

· If you are using a VGA/ SVGA monitor, it will have a male DB-15 connector that plugs into an analog adapter. You should never interchange an analog monitor to that of a digital adapter and vice versa, or severe damage may take place.

5. The storage capacity of various types of floppy:


5 1/4" ---DSHD----1.2MB

3 1/2" ---DSDD----720KB

3 1/2" ---DSHD----1.44MB

3 1/2" ---DSED----2.88MB

DSDD: Double Sided Double Density

DSHD: Double Sided High Density

DSED: Double Sided Extra Density

6. Processor package types:

· 8088, 8086 processors used 40 pin DIPs. 80286,80386, 80486, and some Pentium computers (60MHz, 66MHz) used PGA (Pin Grid Array).

· Pentium chips (75 MHz and above) used SPGA (Staggered PGA). Pentium II CPUs use catridge type mounting method, called "slot-1".

7. Video types:

The table below compares various video types:

Video monitor

Max. Color depth

Max. Resolution


16 Colors



64 colors

640X350 (Graphics Mode)


256 colors

640X480 (Graphics Mode)


16 Million Colors

1280X1024 or even more

8. When you are changing a video monitor on a PC (say, during troubleshooting):

When you are installing a different SVGA monitor, it is likely that the new monitor has the same capabilities as the old one. As a result, the image on the screen may not be readable. In such instances, change the video resolution to Standard VGA before installing the new monitor. You can change the resolution appropriately after the image on the screen is readable with the new monitor. It may also be necessary to load appropriate device driver, if you are installing a different display adapter.

9. FAT file system:

Under FAT file system, the maximum size of a cluster is 32 KB and the maximum number of clusters is 65536. Therefore, the maximum size of a partitions is the number of clusters multiplied by the max size of the cluster, which is equivalent to 2 GB. Remember that 1 KB = 1024 bytes.

10. Real Time Clock:

The Complementary Metal-Oxide Semiconductor (CMOS) allows the computer to store the Real Time Clock (RTC)and other device information even after the computer is switched off and on. This is achieved by using a battery back, just for CMOS.

11. Key board connectors:

Key boards come with two types of connectors. They are:

1. DIN-5, DIN-5 has 5 pins and used with AT style keyboards.

2. Mini DIN-6, also known as PS/2 connector, has around port with 6 pins, one of which being a square pin used for alignment.

12. It is important to know IRQs, and IRQ/ IO conflicts.


Standard Device Assignment

I/O Port Address


System timer






Cascade to IRQ9. Can't be used.


COM ports 2 and 4

COM4: 2E8-2EF
COM2: 2F8-2FF


COM ports 1 and 3

COM3: 3E8-3EF
COM1: 3F8-3FF


Parallel Port LPT2. Very often used for sound cards.

LPT2: 278-27F


Floppy drive controller



Parallel Port, LPT1

LPT1: 378-37F


Real time clock



Unassigned (Also redirected from IRQ2)




Available. SCSI adapter will normally use this IRQ.




Math co-processor.



Primary hard-drive IDE controller

Primary Hard Drive Controller: 1F0-1FF


Secondary hard-drive IDE controller.

Secondary Hard Drive Controller: 0170-0177

  Monochrome Graphic Adapter


  Color Graphic Adapter


-   To determine the COM port assignments, or which COM ports are being used for what, you can use any of the following commands:

1. MODE command

2. DEBUG command

3. MSD

4. Corresponding device applet in the control panel

13. AT Computer interrupt controllers:

An AT computer will have two interrupt controllers. The second interrupt controller need to deliver the interrupts through the primary interrupt controller. IRQ2 had been identified for this purpose on the primary and IRQ9 on the secondary interrupt controllers. In otherwords, IRQ2 and IRQ9 are cascaded.

14. Serial Interfaces:

· COM1, COM2 on a computer uses serial cable. The pin assignments are shown below. The computer acts as a DTE(Data Terminal Equipment) and the Modem acts as DCE (Data Communication Equipment).



DB9 Pin


Received Data



Transmitted Data



Data Terminal Ready






Data Set Ready



Request to Send



Clear to send


Normally, a DTE device connects to a DCE device. If you want to connect two DTR devices, as you would do to hook up two computers via the serial line to exchange files, the cable itself must have cross connections. Such a cable is called null modem cable.

15. RJ – cables:

1. RJ-11: These connectors are used to link modem / phone to the phone line. They have only two pins that get into the modem.

2. RJ-14: RJ-14 connectors are dual-line phone jacks that can accommodate up to 2 telephone line.

3. RJ-45: RJ-45 cable is widely used for attaching UTP cable in LAN environment. These connectors have eight pins.

16. SCSI Types:


Transfer speed




8 bit bus

Fast Wide SCSI


16 bit bus

Wide Ultra SCSI


16 bit bus

Ultra2 SCSI


8 bit bus

Wide Ultra2 SCSI


16 bit bus

Ultra3 SCSI or Ultra 160


16 bit bus


320 MBPS

16 bit bus

SCSI ID - 0=bootable drive, 7=controller, 1-6=any other devices

Wide-Ultra SCSI - 16 devices, 0=bootable drive, 15=controller

17. Each device in a SCSI chain need to have unique ID. For a 16-bit Wide SCSI, there are 16 possible SCSI Ids, 0-15. A standard 8-bit SCSI can support only 8 devices (including SCSI card), the Ids allowed are 0-7.

18. SCSI bus termination:

If the termination is not done, a SCSI devices on the bus will not function properly. This is due to reflection of the signals at the end of the bus. To prevent this, both ends of the SCSI bus need to be terminated. If one end of the SCSI bus is terminated, you may find intermittent problems. Never terminate the bus at a device connected in between.

19. DC voltages commonly found in a PC:

· +5, and +12 volts are the DC voltages commonly found on PCs.80386 / 486 operate at +5v

· Pentium and above operate at +3.3v

· Power supply wires - yellow=+12v, blue=-12v, red=+5v, & white=-5v

20. Tools - Screw driver types:

· A Flat blade screw driver has Minus slot

· A Philips screw driver has X shape slot

· A Torx screw driver has star tip or head

· A Hex screw driver has hex head

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