physical address:

Dealing with PC reverse compatibility requires defeating logic like Gate A20, which forces address rollover to a single megabyte for ancient 8086/8088 compatibility.

After loading the kernel program, we enter protected mode to start up the 386BSD kernel, itself a protected mode program like its own applications.

The 386BSD specification was in two parts - one that detailed getting to a operational system that could build itself and basic console applications, and a more extensive community involvement part, called "A Modest Proposal".

Most popular microprocessors use either segmentation or paging to manage memory address space access. The 386 is rare in that it possesses both. In fact, since segmentation, (see Figure 3(a)), is placed on top of paging (see Figure 3(b)), you are expected to use segmentation in some form any time memory is paged. And, most important, BSD relies on paging.

We initialized the processor with initial descriptor and page tables - one needs to run with the tables before activating memory/interrupt kernel functions.