random access means direct access ie if we have the key then we can directly read that one .
dynamic mode means it is a mixture of both random and sequential access, ie
if we want to read the students of only passed out students of particukar year u have to read like this.
example: actually there are no .of students in the school who belongs to passouts of different years.i want to read read only 2007 passouts i have to skip the passouts up to 2006 and i have to read the students of 2007 in sequential to get all the details of 2007.so this is called dynamic mode of reading .
i think its understanding .