Memory management unit, Operating System

When a program issues a memory load or store operation, the virtual addresses (VAs) used in those operations have to be translated into "real" physical memory addresses (PAs). This translation is themain task of theMMU (MemoryManagement Unit). TheMMUmaintains a page table (a big hash table) that maps virtual pages to physical pages. Since memory accesses are happening all the time, the MMU needs to be extremely fast and implemented correctly. For these reasons, MMUs are almost always implemented in hardware. Note that we can't map every single byte of virtual memory to a physical address; that would require a huge page table. Instead, the MMU maps virtual pages to physical pages. Also, since we want to isolate each program's address space from the address spaces of other applications, the MMU must keep a separate page table for each process; this implies that different processes could use the same virtual address to refer to different data, and that would not be a problem since these virtual addresses would be mapped into different physical addresses. The page table also marks all virtual pages that are allocated (and therefore are being used), so that it is possible to know which virtual pages have valid mappings into physical pages. All virtual pages that are not being mapped to a physical page are marked as invalid; segfaults occur when a program tries to reference or access a virtual address that is not valid. In addition to valid bits, page table entries (PTEs) also store a lot of other information, such as "read" and "write" bits to indicate which pages can be read/written.

Posted Date: 3/12/2013 5:36:07 AM | Location : United States







Related Discussions:- Memory management unit, Assignment Help, Ask Question on Memory management unit, Get Answer, Expert's Help, Memory management unit Discussions

Write discussion on Memory management unit
Your posts are moderated
Related Questions
when demand is 24000 units/year, production rate is 48000 units/year, setup cost is rs 200 per setup, carring cost is rs 20 per units/year, and economic batch quantity is 692.8203

Translation Look aside Buffer In a cached system, the base addresses of the last few indexed pages is maintained in registers named the TLB that adds in faster lookup. TLB has

Enhanced second-chance algorithm. When we increase the second-chance algorithm by considering both the reference bit and the modify bit as an order pair. We have the following

Define multithreading The proficiency of an operating system to execute different parts of a program called threads simultaneously is called as multithreading. A thread is a fl

MEMORY MANAGEMENT USING BUDDY SUSTEM Here we are dividing the memory as powers of two as well as we are selecting the space which is smallest but large enough to hold a process

What are turnaround time and response time? Turnaround time is the interval among the submission of a job and its completion. Response time is the interval among submission

Deadlock Detection and Recovery It's a method of permitting the system to enter a deadlock state, detect it and then recover. Deadlock detection : Is the process of

what is the latest OS of ANDROID in US

#question.explain varios types of system calls..

Define caching. A cache is a region of fast memory that holds copies of data. Access to the cached copy is well-organized than access to the original. Caching and buffering are