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Geek Culture / is it true .com files are only renamed .bin files

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Three Score
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Posted: 6th Jun 2005 05:15
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is it true that a .com file has no header or anything to worry about and is nothing more than pure machine code if u use no header files in the compile

im asking this cause im just building a little testing os(no im nto aiming big it is just a little bit of fun programming when u can do it in C)and im currently using a bootsector by someone else but im not sure if that bootsector loads/strips the .com file so it acts like a .bin file

formerly shadows of emptiness
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Raven
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Joined: 23rd Mar 2005
Location: Hertfordshire, England
Posted: 6th Jun 2005 05:27
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Yes.. and No.
Nice to have a precise answer. heh

.COM are like System in-specific .EXE OS-DEVer.net has more information on them if you'd like to know.

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Posted: 6th Jun 2005 05:37 Edited at: 6th Jun 2005 05:38
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well no i mean for an os
would it be the same as a .bin file
does it have any headers or anything in it
that website could not be found

formerly shadows of emptiness
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empty
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Location: 3 boats down from the candy
Posted: 6th Jun 2005 06:15
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Yes, *.com files have no header.
A com program may not exceed 64k in size (one segment), though.


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Posted: 6th Jun 2005 06:25 Edited at: 6th Jun 2005 07:54
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hmm guess i will be using some jmps and reads then
thank u finally i get an answer

edit:
isnt that only a dos limitation cause it operates in live mode limiting the memory to 64k

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IanM
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Posted: 6th Jun 2005 21:46
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Yes, it *was* a DOS limitation, but windows has inherited that. .com files are assumed to be 16 bit. With .exe files, they have a header that tells the OS what mode they run in.

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Posted: 7th Jun 2005 00:16
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oh because of that dos emulator thing u mean
and that stupid dos emulator does not support mode 13 something newer and older video cards support

i know it is the emulations fault because if i boot my little os from a floppy it works fine but if i run the .com file which should behave the same i get rubish on my montir and have to alt enter to get it out of fullscreen

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