What is checksum???

What is checksum??

 

A checksum is a number which is calculated by some method using the data contained in a file. When the file is written this number is included in the file. When the file is read later, the reading program examines the data and calculates the checksum and then compares it with the one recorded with the file. If they agree then the data in the file is the same and the file is good.

The name comes from the the early ways of calculating it. The bits were literally just added up and when the higher order bits overflowed when the number got bigger than the number of bytes allocated for it they were just thrown away.

Nowdays much more sopisticated methods are used to calculate the number such that it is virtually impossible for a file with bad data to coincidently have the same as the correct checksum.

You can look up things like: CRC32, MD5

 

EXCELLENT..................thank you

 

Is this also how ati validates a backup?

 

Yes, but I don't know if there is one or several checksums in an archive and any other details.

The checksum method is the reason TI can validate an archive at any time and on any machine. If it needed to do a bit comparison it would have to have the source in its original form to do the compare. Impossible when making a backup within Windows.

 

Also, impossible when making a backup outside of windows.

THere are two important things:

1. Verifying that th earchive is self-consistent. This is done by using checksums.
2. Seeing how an archive, which is merely a snapshot at a point in time, differs from the files on t source drives at appropriate points in time.

Thus is done by using programs such as the following:

http://www.standards.com/index.html?ReadFile
http://www.standards.com./index.html?GetFileTypeDistribution
http://www.standards.com./index.html?CompareDrives

 

Hello max0071,

Thank you for choosing Acronis Disk Backup Software.

I am sorry for the delayed response.

Please note that when Acronis True Image creates the image archive the Snapshot Manager driver creates a point-in-time view of the system volume (snapshot of the entire hard drive/partition in its current state) and also the checksum is calculated. This checksum stores in the image. When Acronis True Image validates the image archive it calculates the checksum and compares this "new" checksum with the one in the image. If this values is identical then the image archive validates successfully and the restoration is possible.

Thank you.
--
Aleksandr Isakov