Virtual Memory Organization

Lecture ? 9

Virtual Memory

The goal of the lecture : analyze and study virtual Memory Techniques, virtual Memory Address translation, use of an associative-mapped TLB.

Contents

1. Virtual Memory Techniques.

2. Virtual Memory Address translation.

3. Use of an associative-mapped TLB.

Literature.

1. Stallings W. Computer Organization and Architecture. Designing and performance, 5^th ed. ? Upper Saddle River, NJ : Prentice Hall, 2002.

2. V. Carl Hamacher, Zvonko G. Vranesic, Safwat G. Zaky. Computer organization,4^th ed. ? McGRAW-HILL INTERNATIONAL EDITIONS, 1996.

Tanenbaum, A.S. Structured Computer Organization, 4^th ed. - Upper Saddle River, NJ : Prentice Hall, 2002

Virtual-memory Technique

Usually only some parts of a program that are executed are first brought into the main memory; when a new part (segment) of a program is to be moved into the full memory, it must replace another segment already in the memory. In modern computers, the operating system moves programs and data automatically between the main memory and secondary storage.

Techniques that automatically move program and data blocks into a physical main memory when they are required for execution are called virtual memory techniques.

The virtual memory mechanism bridges the size and speed gaps between the main memory and secondary storage and is usually implemented in part by software techniques.

Programs, and hence the processor, reference an instruction and data space, that is independent of the available physical main memory space. The binary addresses that the processor issues for either instructions or data are called virtual or logical addresses.

These addresses are translated into physical addresses by a combination of hardware and software components. If a virtual address refers to a part of the program or data space that is currently in the physical memory, then the contents of appropriate location in the memory are accessed immediately. On the other hand, if the referenced address is not in the main memory, its contents must to be brought into a suitable location in the main memory before they can be used.

The figure Virtual Memory Organization shows a typical organization that implements virtual memory. A special hardware unit, called Memory Management Unit (MMU), translates virtual address into physical address. When the desired data are in the main memory, these data are fetched as of the cache mechanism. If the data are not in the main memory, the MMU causes the operating system to bring the data into the memory from the disk. Transfer of data between the disk and the main memory is performed using the DMA.

Virtual Memory Organization

Date: 2016-06-13; view: 7