Why is it so that my 8GB ROM Android smart-phone has only 4GB available internal space? - Quora

The ROM is partitioned with different size allocation for different purposes like:-

1. 2–3 GB for you OS as read only partition.
2. Then you have caches
3. Internal storage, where you normally store your files.

You can't change the allocations normally, but after gaining root access you can change them.

Why is it so that my 8GB ROM Android smart-phone has only 4GB available internal space?