varchar memory allocation

[ravi suthar]

I have one doubt in terms of Database/OS..
We know the VARCHAR is variable length Datatype. I am taking
vName varchar(20)= "Test"
so it will occupy only 4 char's memory and later 16 char's will be discarded as VARCHAR is used. But when I update the same field with "TESTDATA" then How will other 4 chars will be stored/managed ??
If any of you have idea on this issue,then let me know.

[Wendy L Gibbons]

are you asking about memory in the database? or in your VM?

as to be honest I have never cared, it works so haven't spent any thought on it.
How do collections work in java by the VM doing memory allocation and de-allocation for you, it is the same concept.