A+ certification study notes on hardware

A+ Certification : 220-1001

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1. Some important acronyms:

2. There are basically two important types of RAM:

SRAM, being expensive, primarily used for Cache memory. DRAM, being cheaper, is used for main memory. SRAM is widely used for Level 1, Level 2 or Level 3 cache memory. Level 1 cache is internal to the processor, and level 2 and level 3 caches are external to the processor, it resides on the motherboard.

DRAM: Dynamic RAM holds its data if it is continuously accessed by special logic called a refresh circuit. If the memory is not refreshed regularly, then the DRAM will lose its contents. This refreshing action is why the memory is called dynamic.

3. PC Memory cards:

4. Monitor Connectors:

5. The storage capacity of various types of floppy:




5 1/4"



3 1/2"


3 1/2"



3 1/2"



3 1/2"



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:

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

IRQ Standard Device Assignment I/O Port Address
0 System timer 40Hex
Keyboard 60Hex
1 Cascade to IRQ9. Can't be used.
2 COM ports 2 and 4 COM4: 2E8-2EF
COM2: 2F8-2FF
3 COM ports 1 and 3 COM3: 3E8-3EF
COM1: 3F8-3FF
4 Parallel Port LPT2. Very often used for sound cards. LPT2: 278-27F
5 Floppy drive controller 3F0-3F7
6 Parallel Port, LPT1 LPT1: 378-37F
7 Real time clock 70Hex
8 Unassigned (Also redirected from IRQ2)
9 Available
10 Available. SCSI adapter will normally use this IRQ.
11 Available
12 Math co-processor. F0Hex
13 Primary hard-drive IDE controller Primary Hard Drive Controller: 1F0-1FF
14 Secondary hard-drive IDE controller. Secondary Hard Drive Controller: 0170-0177
15 Monochrome Graphic Adapter 3B0-3BF
16 Color Graphic Adapter 3D0-3DF

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

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:

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



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:

20. Tools - Screw driver types:

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