Memory adressing

Chapter-  Memory addressing

This chapter deals with addressing techniques .An operating system is not forced to keep track of physical memory all by itself.
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:
1-Logical address   2-Linear address ( virtual address)  3- Physical address
1-Logical address :logical address is machine language instruction(operand) by CPU.
 Each logical address consists of a segment and an offset (or displacement) that denotes the distance from the start of the segment to the actual address.
2-Linear address :A single 32-bit unsigned integer that can be used to address up to 4 GB—that is,up to 4,294,967,296 memory cells. Linear addresses are usually represented in hexadecimal notation; their values range from 0x00000000 to 0xffffffff .
3-Physical address:Used to address memory cells in memory chips. They correspond to the electrical signals sent along the address pins of the microprocessor to the memory bus.Physical addresses are represented as 32-bit or 36-bit unsigned integers.

The Memory Management Unit (MMU) transforms a logical address into a linear address by means of a hardware circuit called a segmentation unit; subsequently, a second hardware circuit called a paging unit transforms the linear address into a physical address.