When it starts up,
boot26 displays the current memory map. Each character in the map represents one page of (physical) RAM. The ticks along the top are to stop you getting lost. The characters in the map indicate what the memory's being used for (actually where it's logically mapped):
0 -> zero-page
+ -> boot26 workspace
* -> Free space (boot26 wants to put the kernel here)
d -> RAM disc
s -> System sprite area
m -> RMA
h -> System heap/stack
f -> Font cache
S -> Screen memory
On a machine with 32k pages (which is all
NetBSD/acorn26 supports), the left half of the first line is potential screen memory, and hence not used by
boot26. The next page is usually zero page under RISC OS, and is used for zero page under
NetBSD as well. The next is usually the system heap under RISC OS, and is used for process 0's kernel stack under
NetBSD. The next is used for the message buffer under
NetBSD. Pages from there on are used to load the kernel, and must be free if
boot26 is to do so successfully. Future bootloaders should load the kernel into whatever pages are free, then kick out RISC OS and shuffle them into the right shape. This is left as an exercise for the enthusiastic reader.