Consider the situations which cause a computer to hang up while booting or hang up due to data loss.
Zeros are written to the location of the first partition entry.
Physical Sector: Cyl 0, Side 0, Sector 1 0000001B0 80 00 ..............€. 0000001C0 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................ 0000001C0 41 3F 06 FE 7F 64 7F 32 4E 00 A6 50 09 00 00 00 A?.?d2N.¦P.... 0000001D0 41 65 0F FE BF 4A 25 83 57 00 66 61 38 00 00 00 Ae.??J%?W.fa8... 0000001F0 00 00 00 00 00 00 00 00 00 00 00 00 00 00 55 AA ..............U?
By trying to boot now, the MBR loader will try to read and interpret the zeros (or other garbage) as partition parameters and an error message like "Missing Operating System" will appear.
Thus, the second step in partition recovery is to run a Disk Viewer and make sure that the proper partition exists in the partition table and has been set as active.
It contains all the necessary information about the partition so that if recovery software finds it, it can reconstruct the partition entry in the Partition Table. (see Partition Boot Sector topic for details).
In this case, a new partition would exist instead of the original one. Everything would work properly with the exception that you could not go back to the original partition if important data is still there. If you've created a MBR, a Partition Table, or a Volume Sectors backup beforehand (as can be done with Active@ Partition Recovery and Active@ UNERASER for example), you can virtually restore it and look for your data (if it has not yet been overwritten by new data).
Some advanced recovery tools also have an ability to scan disk surfaces and try to reconstruct previously deleted partition information from the pieces of left over information (i.e. perform virtual partition recovery). However it is not guaranteed that you can recover something.
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