Memory Services

Contents:

General
Standard API
Page Allocation Map (PAM)
System Page Directory

The memory services is responsible for managing physical memory, GDT descriptors and LDT descriptors. It manages physical memory via a table called the PAM.

This table has a word entry for each physical page. The entry normally contains the descriptor number for the code that owns the page. Exceptions to this are:

 

Value	Meaning
0x0000	Page free
0xFFFE	Module code seg.
0xFFFF	Page unuseable

 

 

Value	Meaning
0	Allocated as DMA
1	Allocated as common
2	Allocated as user code
3	Allocated as user data

 

This is the address of a page used for a normal page directory (see intel's programmers guides). It maps common memory (first 1Gb of physical memory) to the linear space. The memory manager can use this as a template when creating address spaces for applications. It is also used by system tasks (drivers, etc).