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Memory Manager in Windows XP

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luqman cullens

on 17 December 2013

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Transcript of Memory Manager in Windows XP

Memory Manager in Windows XP
Introduction to Windows
Memory Manager in Windows XP
Virtual Memory andOS Maps Virtual Addresses to Physical Addresses
INTRO Part 2
Windows XP presented a significantly redesigned graphical user interface, a change Microsoft promoted as more user-friendly than previous versions of Windows.
Windows XP was available in many languages.
The maximum total number of logical processors in a PC that Windows XP supports is: 32 for 32-bit, 64 for 64-bit.
Memory Management??
Memory management in Microsoft Windows operating systems has evolved into a rich and sophisticated architecture.
Virtual memory manager (VMM)
– Executive component responsible for managing memory
• Lazy allocation
– Avoid allocating memory until necessary
• Prefetching
– Move pages from disk to main memory before they are needed
• Pagefile
– Stores pages that do not fit in main memory
– Windows XP supports up to 16 pagefiles
Memory organization
32-bit virtual address space
– Windows 64-Bit Edition has 64-bit address space.
– 4GB virtual address space per process
• User space vs. System space
– Process can access only user space
– VMM stores page tables and other data in system space
– 2GB user space, 2GB system space
• 4KB pages
Memory Organization
2-level hierarchical memory map
– Page directory table
• Page directory entries (PDEs) point to page table
• One page directory table per process
• Location in page directory register
– Page table
• Page table entries (PTEs) point to page frames
– Page frame
• Contains page of data
• TLB accelerates address translation
Memory Organization
Virtual Memory
virtual memory is a memory management technique that is implemented using both hardware and software.
It maps memory addresses used by a program, called virtual addresses, into physical addresses in computer memory
address space or collection of contiguous segments. The operating system manages virtual address spaces and the assignment of real memory to virtual memory.
Detail 2
Windows XP is an operating system produced by Microsoft for use on personal computers.
It’s including home and business desktops, laptops and media centers.
It is the second most popular version of Windows, based on installed user base.
The name "XP" is short for "eXPerience“.
NT-based versions of Windows, which are programmed in C, C++, and assembly, are known for their improved stability and efficiency.
INTRO part 1
The primary benefits of virtual memory include freeing applications from having to manage
shared memory space,
increased security due to memory isolation,
being able to conceptually use more memory than might be physically available.
using the technique of paging.
The OS Maps Virtual Addresses to Physical Addresses.
Because the virtual address space might be larger or smaller than the physical memory on the machine, the Windows Memory Manager has two first-in-rank responsibilities
The first is to translate, or map, a process's virtual address space into physical memory
The second one is paging some of the contents of memory to disk when it becomes overcommitted
Memory-mapping can speed-up sequential file processing due to the fact the data is not sought randomly
Memory Leaks?
Definition : memory leak occurs when a computer program incorrectly manages memory allocations.
A memory leak has symptoms similar to a number of other problems and generally can only be diagnosed by a programmer with access to the program.
Because they can exhaust available system memory as an application runs, memory leaks are often the cause of or a contributing factor to software aging.
Consequnce : a memory leak can diminish the performance of the computer by reducing the amount of available memory. In modern operating systems, normal memory used by an application is released when the application terminates.
( means that a memory leak in a program that only runs for a short time may not be noticed and is rarely serious)

Much more serious leaks include those:
-where new memory is allocated frequently for one-time tasks,
-where the program can request memory
-where memory is very limited, such as in an embedded system or portable device.

Effect : - if a program has a memory leak and its memory usage is steadily increasing, there will not usually be an immediate symptom.- When all the memory on a system is exhausted, any attempt to allocate more memory will fail. - If the memory leak is in the kernel, the operating system itself will likely fail.

Example : written in pseudocode, is intended to show how a memory leak can come about, and its effects, without needing any programming knowledge. The program in this case is part of some very simple software designed to control an elevator. This part of the program is run whenever anyone inside the elevator presses the button for a floor.

Virtual address translation.
• PTE can point to data in pagefile
– 4 bits determine which pagefile
– 20 bits indicate offset in pagefile
• PTE has five protection bits
– Read
– Write
– Execute
– Copy-on-write
– Raise exception on access
• PTE has three state bits
Memory Organization
group 3

In this chapter, we’re examined how the windows memory manager implements virtual memory management.
As with most modern operating systems, each process is given access to a private address space, protecting one process’s memory from another’s but allowing processes to share memory efficiently and securely.
Advanced capabilities, such as the inclusion of mapped files and the ability to sparsely allocate memory, are also available.
So, we have know details about memory manager in windows xp
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