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  1. Junior Member
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    Jan 2006
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    Taxachusetts
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    #1

    Default How to Memorize COM ports and I/O Addresses...

    Here's a little trick I came up with that you might find useful...


    COM1 - 03F8
    COM2 - 02F8
    COM3 - 03E8
    COM4 - 02E8


    Now, to use the trick, first look and the number after 0. We'll use 02F8 in the example.

    02F8

    This number can tell us if the COM port will be odd or even. In this case, the first number after 0 is 2, an even number. So, the COM port will be even as well, COM2 or COM4.

    In the next part we can look at is the letter after that number.

    02F8

    I like to think that "F" stands for first. So, if the letter if "F", it's the first in its odd or even pair, COM1 in the odd pair or COM2 in the even pair. I haven't come up with what "E" could stand for, but by elimination you know it's the second in its pair if it's not "F" for first - COM3 or COM4. In this case, the letter is "F", so we know that this I/O address is first in it's pair.

    When we put this information together, we can determine that 02F8 is the first in the even pair, or COM2.

    I hope you find it helpful. It seems a bit complicated at first, but once you understand it, it's invaluable.
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  3. Senior Member
    Join Date
    Dec 2005
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    154

    Certifications
    A+ Network+ MCP (70-270, 70-290)
    #2
    The "E" stand for "Extra". I saw that example somewhere on this board or in one of the books I read about that portion of the test. That's a good way to remember it and you will definitely need to know your IRQ's, COM's, and I/O's.
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  4. Member
    Join Date
    Dec 2005
    Location
    Mexico
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    Network+ , A+ , MCP ( 271)
    #3

    Default I just imagined a matrix

    COM1 - IRQ4 03F8
    COM2 - IRQ3 02F8
    COM3 - IRQ4 03E8
    COM4 - IRQ3 02E8

    Take a close look to the matrix the second colum has something in common. 4-3-4-3 and the third one 3-2-3-2
    Just learn that sequence and you will remember that, imagine the matrix
    And for the letter order just remember the word " FE " FF.EE
    and you will remember that the first two address are FF and Second EE

    jeje greets
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  5. Junior Member
    Join Date
    Dec 2005
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    13
    #4
    I have dumber way of rememberin this.

    IRQ 0- System clock
    IRQ 1- Keyboard
    IRQ 2- (2 & 9 linked)
    IRQ 3- It is Com2's Fate (2F to be IRQ3. It is Com4's fate to bE late (2E
    IRQ 4- It is Com1's Tripple Fate (3F to be IRQ4. It is Com3's fate to bE late (3E
    IRQ 5- The Liberation of Palestine Terrorists have 2 gods (LPT2) and they attacked twice in 1978. (27
    IRQ 6- Floppy has six letters therefor it is IRQ 6
    IRQ 7- Little Paul Trammel has one Toy (LPT1) and he was lost 3 times in 1978 (37
    IRQ 8- Realtime clock has eight letters so it is IRQ8
    IRQ 9- (2&9 linked)
    IRQ 10- Red light district (open for business)
    IRQ 11- Red light district (open for business)
    IRQ 12- Mighty_MOUSE has twelve characters (including space) therefor it is IRQ12
    IRQ 13- Mathco processors are evil so they go on IRQ13
    IRQ 14- Primary IDE has one foe because it is primary. (1F0)
    IRQ 15- Secondary IDE has 170 foes be cause it is last. (170)
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  6. Member
    Join Date
    Aug 2005
    Location
    Colorado
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    A+, Network+
    #5
    With the IRQ's I made up some flash cards and went through them A BUNCH of times. as for the IO's here's a tip I saw here on this web site.

    Memorizing I/O Addresses
    There are 9 addresses, they are all in 3 digit hexadecimal format. Each one ends in the number "8 or 0". But the first two hex digits vary with each address. So remember this mnemonic:


    3 2 3 2 3 2 1 1 3 F F E E 7 7 F 7 F 8 8 8 8 8 8 0 0 0

    Now write the 3s,2s 1s and the3 as a column:
    3
    2
    3
    2
    3
    2
    1
    1
    3
    And add the rest as a second column:
    3F
    2F
    3E
    2E
    37
    27
    1F
    17
    3F
    Now add an "8" to the first 6 & 0s to the remaining 3 end of each row.
    3F8
    2F8
    3E8
    2E8
    378
    278
    1F0
    170
    3F0
    That is a list of all 9 addresses. And, in order, they correspond to COM 1,2,3,4 and LPT 1 and 2, Prim IDE Second. IDE & Floppy.

    3F8: COM 1
    2F8: COM 2
    3E8: COM 3
    2E8: COM 4
    378: LPT 1
    278: LPT 2
    1F0: Primary IDE
    170: Secondary IDE
    3F0: Floppy

    All you need to remember "3-2-3-2-3-2-1-1-3-F-F-E-E-7-7-F-7-F-8-8
    ? 8-8-8-8-0-0-0
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  7. Junior Member
    Join Date
    Feb 2006
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    6

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    A+
    #6
    I really can't believe they still have this kind of stuff on the A+ exams. In the real tech world, you encounter one of these IRQ deals in a million. At that point, it's time to get a new computer, or to consult a little manual outlining the IRQ stuff. I suppose when you start dealing with SCSI you might get this? But who really needs expensive SCSI anymore? Is it really that advantageous?

    -Allan Nevala
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