Standard DOS MBRs (they have slightly different code for different DOS versions and other operating systems) then analyze the partition table to find a primary, active DOS partition, and, if found, (there are other conditions depending on the DOS version among other things) the first sector of that logical partition (the operating system boot sector) is loaded into memory and execution passes to it (and that traditionally bootstraps the operating system proper). It contains (at a minimum) some executable code to start the bootstrap of the operating system, a 64 byte data area known as the partition table and a two byte signature (that some BIOSes reputedly do not check for).Īssuming that the basic BIOS hardware integrity tests pass and the BIOS configuration is set to allow booting from a hard drive, at power-up the MBR will be copied from the disk and execution passes to the beginning of the MBR. There are some special things about the MBR. The Master Boot Record (MBR) of a PC’s hard drive is the very first physical sector on the disk (0,0,1 in head, cylinder, sector terms). To understand what it does, first we have to get some terminology clear. Please do not further use the material without obtaining your own permission to use it.īefore describing what can to wrong, let’s first see what the command does… The following detailed description was posted to comp.virus by Nick FitzGerald and is used here with permission.

But, understand that there are good reasons why the /MBR parameter was undocumented (it’s largely known now). One “cure” for partition sector viruses suggested by people who think they know what they are doing is the FDISK command using the parameter /MBR. FDISK /MBR is often suggested as a solution for fixing a virus attack.The simple advice is: Just Don’t Do It!

Mbr disk format