Four Megabytes Of Nothing

A machine has a 32-bit virtual address space, 4 KB pages, and a linear page table with 4-byte entries. A process runs int main(void) { return 0; } and touches perhaps eight pages in its life.

Select every statement that is true. More than one applies.

Marking the unused entries invalid saves physical frames for the pages, but saves nothing in the page table itself.

Each entry has to store the 12-bit page offset alongside the frame number, which is where a quarter of the 4 bytes goes.

The table has $2^{20}$ entries and occupies 4 MB, regardless of how few pages the process actually touches.

Running 100 such processes costs about 400 MB of physical memory for translations alone.

The table shrinks to match what the process touches, because entries exist only for pages that have been mapped.