I digged into the problem and found that SHA1 checksum was the same.
Wrote my own checksum code and yes, the original file and the merged file are the same.
Gsplit works correctly. The checkum program does not.
No idea why MD5 checksum was different.
The original file is on a XP machine.
The merged file is on a w7 machine.
Could this be the cause ?
Anyway: sorry for my lack of faith and for raising false alarms 
Duilio
Dear Sir,
I split a large 35GB VMDK file into several GSD file of 1GB each .
I moved the GSD files to another PC and united the pieces.
As a result, I got a new file that has exactly the same number of bytes as the original VMDK file ( 36.148.412.416).
However, the MD5 checksum is different.
The old checksum was
35b11d6ca290ededebe1115a09b51116
the new checksum is
e0d16dd0f3e3b63c350021db824c5d11
I evalued the checkum using
You may have a bug in your product that shows when using large files or splits.
Thank you
Duilio
Thank you for the follow-up. It was a bit strange that it didn’t work fine, because GSplit is widely used and even for files larger than 35 GB.
So the question is: does the MD5 program handle very large files?