Confusion about media descripter byte in OEM block

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Confusion about media descripter byte in OEM block

Postby brainbarshan » Sat Feb 20, 2010 2:58 pm

In tutorial 5 (Bootloaders 3) of operating system developement series :

The Media Descriptor Byte (bpbMedia) is a byte code that contains information about the disk. This byte is a Bit Pattern:
Bits 0: Sides/Heads = 0 if it is single sided, 1 if its double sided
Bits 1: Size = 0 if it has 9 sectors per FAT, 1 if it has 8.
Bits 2: Density = 0 if it has 80 tracks, 1 if it is 40 tracks.
Bits 3: Type = 0 if its a fixed disk (Such as hard drive), 1 if removable (Such as floppy drive)
Bits 4 to 7 are unused, and always 1.


so for floppy disk we have to set 11111000 = 0xF8, because 3rd bit to be set is 1 ( for floppy drive , as mentioned)

but the 3rd bit has been set 0 and so the byte is set 0xF0.
which one is correct?
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Re: Confusion about media descripter byte in OEM block

Postby Mike » Thu Mar 11, 2010 7:50 pm

Hello,

I apologize for the late reply. We need to verify the information in that table is correct. For 1.44 MB (and 2.88 MB) media the media descriptor byte should be 0xf0 not 0xf8.
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