On (17 Jun 94) Rod Speed wrote to Paul Edwards...



 PE> Remember when my hard disk was stuffed you told me to do an "fdisk

 PE> /mbr"?



 RS> Yep.



 PE> Well I have found a book (from David Begley), which tells me about

 PE> the master boot record, and it has the partition information in it.



 RS> Well, its more accurate to say that the first physical sector on

 RS> the drive you are going to boot from has various stuff in it like

 RS> the partition table and the MBR. When you use the FDISK /MBR

 RS> command you rewrite JUST the MBR and dont touch the partition table

 RS> which is also in that sector.



 RS> The first sector also has the bios parameter block, various detail

 RS> of the drive, which OS formatted it, how many sectors there are

 RS> etc.



 PE> How come you made it sound like "fdisk /mbr" was an innocuous

 PE> command?



 RS> Because all it does is rewrite the loader which is used to load the

 RS> first bit of DOS proper off the bootable drive. Its just a small

 RS> piece of code and so its completely safe to rewrite that small

 RS> piece of code. The FDISK /MBR doesnt touch the partition table or

 RS> the BIOS parameter block.



partly true, since it is impossible to write less than 1 sector on a

disk (at least all the ones that i have ever come across, although you

no doubt know of an exception) the partition table, although it is not

altered, must be read from the disk and re-written to it.



[to paul]

if you really wish to feed your paranoia, consider this - my pc at work

has a "virus detector" in the bios. one of the things that it does is to

monitor attempts to alter the mbr (a characteristic of some viruses).

this machine has os/2 and dos on it with a dual boot partition, if you

boot dos, the virus detector comes up and asks you to authorise an

attempt to write to the mbr. it does not do this if you boot os/2. i

dont know what it is doing there, maybe it is counting down to destroy

dos after x number of boots, but every time you boot dos, os/2 fudges

with the mbr.



                            keith



... The buck doesn't even slow down here.



--- PPoint 1.80


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