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

RustedChainsawRustedChainsaw Member Posts: 1 ■□□□□□□□□□
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.


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.


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.


  • Go BucksGo Bucks Member Posts: 152
    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.
    "Me fail English? That's unpossible."
  • jsobrinogjsobrinog Member Posts: 54 ■■□□□□□□□□
    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
  • Majestic_LizardMajestic_Lizard Member Posts: 13 ■□□□□□□□□□
    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 (2Ficon_cool.gif to be IRQ3. It is Com4's fate to bE late (2Eicon_cool.gif
    IRQ 4- It is Com1's Tripple Fate (3Ficon_cool.gif to be IRQ4. It is Com3's fate to bE late (3Eicon_cool.gif
    IRQ 5- The Liberation of Palestine Terrorists have 2 gods (LPT2) and they attacked twice in 1978. (27icon_cool.gif
    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 (37icon_cool.gif
    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)
  • dbjjonesdbjjones Member Posts: 32 ■■□□□□□□□□
    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:
    And add the rest as a second column:
    Now add an "8" to the first 6 & 0s to the remaining 3 end of each row.
    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
  • Allan NevalaAllan Nevala Member Posts: 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
Sign In or Register to comment.