Understanding the Linux Kernel, Second Edition

Chapter 2. Memory Addressing

This chapter deals with addressing techniques. Luckily, an operating system is not forced to keep track of physical memory all by itself; today’s microprocessors include several hardware circuits to make memory management both more efficient and more robust in case of programming errors.

As in the rest of this book, we offer details in this chapter on how 80 × 86 microprocessors address memory chips and how Linux uses the available addressing circuits. You will find, we hope, that when you learn the implementation details on Linux’s most popular platform you will better understand both the general theory of paging and how to research the implementation on other platforms.

This is the first of three chapters related to memory management; Chapter 7 discusses how the kernel allocates main memory to itself, while Chapter 8 considers how linear addresses are assigned to processes.

Memory Addresses

Programmers casually refer to a memory address as the way to access the contents of a memory cell. But when dealing with 80 × 86 microprocessors, we have to distinguish three kinds of addresses:

Logical address

Included in the machine language instructions to specify the address of an operand or of an instruction. This type of address embodies the well-known 80 × 86 segmented architecture that forces MS-DOS and Windows programmers to divide their programs into segments. Each logical address consists of a segment and an offset (or displacement ) that denotes ...