Rolling Your Own Bootloader: Difference between revisions

You will have to decide where in memory you are going to load your kernel. Your kernel generally depends on it.

 

 

If your kernel is bigger (or is expected to grow bigger) than this, you'll probably prefer to have the kernel above the 1MB barrier, which means you need to activate [[A20 Line|A20 gate]] and switch to [[Unreal Mode]] to load the kernel (with A20 alone, you cannot have more than 64K above 1MB).

If you're loading above 1MB, you should proceed in 2 steps: first using BIOS to load in the "conventional" area, and then performing a <tt>rep movsd</tt> to place the data where they ultimately should go.

 

 

The next step consist of collecting as much information as you can/need: [[How Do I Determine The Amount Of RAM|amount of installed RAM]], available [[Getting VBE Mode Info|video modes]] and things alike are easier to do in real mode, so better do them while in [[Real Mode]] than trying to come back to real mode for a trip later. Of course the exact requirements depend on your kernel.

 

 

<pre>