are you sure?
80 -to 100Gb these days is par for a hard drive and mostly less on a typical proprietary machine. such as Dell
If you are not sure exactly what your machine has down load this utility click here
Then compare it with what the original spec was/is
It can be true that machines such as Dell and a few others prove to be difficult to work on because these firms built to a formulas with special parts that are not always compatible or upgradable.