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CS554 RESEARCH PROJECT 2 MEMORY MANAGMENT AND VIRUAL MEMORY 1

Project 2 for CS554 Research Option

Memory Management and Virtual Memory

Author: Nagunuri Abhinav

Date: 03-08-2014

Course name:CS554BH1


ABSTRACT

Memory management is the process of controlling and guiding the computer memory, assigning

portions called blocks to various running programs to control overall system performance.

Memory management is present inside hardware in the operating system, and in programs and

applications. Virtual memory is a memory management technique that is implemented using

both hardware and software also. this maps memory address used by a program, called virtual

addresses into physical addresses in computer memory. The main storage as seen by a process

or collection of contiguous segments .


TIITLE CONTENTS PAGE NO

Introduction .................................................................................... 4

Full operating system identification..................................................... 5

Memory capacity ................................................................................... 8

Process Protection.................................................................................. 8

Memory Allocation................................................................................ 9

Memory Mapping.................................................................................. 11

Conclusion.............................................................................................. 13

References................................................................................................ 13


Introduction :

An operating system OS is a collection of software that manages computer

hardware resources and provides common services for computer programs. The operating system

is an essential component of the system software in a computer system. Application programs

usually require an operating system to function.

Time-sharing operating systems schedule tasks for efficient use of the system and may

also include accounting software for cost allocation of processor time, mass storage, printing, and

other resources. The data in this operating system is managed by memory management.

Memory management

Memory management is the process of controlling and guiding the computer

memory, assigning portions called blocks to various running programs to control overall system

performance. Memory management is present inside hardware in the operating system, and in

programs and applications

In hardware, memory management involves components that store data, such as RAM

,micro and macro chips , memory caches, and flash-based solid-state drives. In the OS, memory

management involves the allocation of specific memory blocks to individual programs as user

demands change. when the program requests a block of memory, a part of the memory manager

called the allocator assigns that block to the program. When a program no longer needs the data

in previously allocated memory blocks, those blocks become available for reassignment.

Virtual memory


Virtual memory is a memory management technique that is implemented using both

hardware and software also. this maps memory address used by a program, called virtual

addresses into physical addresses in computer memory. The main storage as seen by a process

or collection of contiguous segments .The operating system manages virtual address spaces and

the assignment of real memory to virtual memory.Address translation hardware in the CPU, often

referred to as a Memory management unit automatically translates virtual addresses to physical

addresses.Software within the operating system may extend these advantages and capabilities to

provide a virtual address space that can exceed the capacity of real memory and thus reference

more memory than is physically present in the computer. The primary benefits of virtual memory

include freeing applications from having to manage the shared memory space, increased

security due to memory isolation, and being able to continously using more memory than might

be physically available, using the technique of paging.

Full Operating System Identification

Microsoft Windows 7 was an operating system produced by Microsoft for use on

personal computers, including home and business desktops, laptops, net books ,Notes , and other

media center computers. It was released to manufacturing on July 22,2009 and became a good

product available for retail worldwide on October 22, 2009, Microsoft co founders are Bill gates

and Paul Allen .Windows 7 is of 6.1 version which is highest than Windows vista that is 6.0

version Its a Windows Updated , Hybrid is of kernel type, Unlike Windows Vista, which

introduced many new features, Windows 7 was an upgrade designed to work with Vista-

compatible applications and hardware. Presentations given by Microsoft in 2008 focused on

multi touch support, an updated Windows shell with a new task bar home networking system


called Home Group and performance improvements. Some standard applications that have been

included with releases.

The main features in Windows 7 are

SPEED

Even aside from incompatibilities and other issues that many people had with Vista, one

of the most straightforward was speed it just felt too sluggish compared to XP, even on pumped

up hardware. Windows 7 brings a more responsive and sprightly feel and Microsoft has spent a

lot of time and effort getting the Start Menu response just right.

COMPATIBILITY

The compatibility on Windows 7 will be far better than it was with Vista. Many programs

that individuals and companies used on Windows XP did not work immediately and required

several updates, but with Windows 7 almost all applications that work on Vista should still run.

LOWER HARD WARE REQIREMENT

Vista gained a reputation for making hardware look rather ordinary. Windows 7,

however, will run well on lower end hardware, making the transition from Window XP less

painful

SEARCH AND ORGANISATION

One of the best things about Windows 7 is the improved search tool, For example, typing

mouse will bring up the mouse option within the control panel or typing a word will display it

and split it up neatly into files, folders and applications.


START MENU

The task bar looks like nothing has much has changed . but their was a dramatic look

Infact, thats not the case and its a lot more powerful. Microsoft is now making best use of its

aero technology.

AERO-SHAKE

Our new visual feature is called Aero Shake. If you have a more number of things to

open the Windows open but want to focus on just the one you can all you have to do is grab it by

the title bar and shake with the mouse. .

STACKING

Another great touch is Stacking. You simply drag a Window to the sides of your screen

and it will stick automatically to the side filling half the screen, making it quick and easy to view

documents side by side. Move to the top and it will

maximize to the whole screen.

GAMMA CURVE

The display properties now boast a useful gamma curve feature enabling you to calibrate

your display. Set aside 10 minutes to go through it carefully and you can really give your monitor

image a boost, which will pay dividends when youre sitting in front of a screen all day.

TOUCH


The visual feature to come to Windows 7 is its touch capability. This will only be

available to those with a touch enabled PC, such as HPs Touch Smart range, but for those

suitably equipped it will provide a new way of interacting with their PC and with other.

Memory Capacity

Each process on 32-bit Microsoft Windows has its own virtual address space that enables

addressing up to 4 gigabytes of memory. Each process on 64-bit Windows has a virtual address

space of 8 terabytes. All threads of a process can access its virtual address space. However,

threads cannot access memory that belongs to another process, which protects a process from

being corrupted by another process.

The virtual address space and the memory management functions can be known by detail study

on Virtual Address Space,Memory Pools,Memory Performance Information,Virtual Memory

Functions,Heap Functions.

Process protection

Windows security model enables you to control access to process objects. When a user logs in,

the system collects a set of data that uniquely identifies the user during the authentication

process, and stores it in an access token. This access token describes the security protocol to of

all processes associated with the user. You can use a token to specify the current security context

for a process using the Create Process With TokenW function. You can specify a security

descriptor for a process when you call the Create Process, Create Process As User,

orCreateProcessWithLogonW function. If you specify NULL, the process gets a default security

descriptor. The ACLs in the default security descriptor for a process come from the primary or

impersonation token of the creator. If a computer system has multiple users and allows the


concurrent execution of multiple processes, then access to data must be regulated. For that

purpose, mechanisms ensure that files, memory segments, CPU, and other resources can be

operated on by only those processes that have gained

proper authorization from the operating system.Some of the following specific access rights are

not allowed from a process to a protected process:

PROCESS_ALL_ACCESS PROCESS_CREATE_PROCE

PROCESS_CREATE_THREAD PROCESS_DUP_HANDLE

PROCESS_QUERY_INFORMATION PROCESS_SET_INFORMATION

PROCESS_SET_QUOTA PROCESS_VM_OPERATION PROCESS_VM_READ

PROCESS_VM_WRI

Memory Allocation

The following is a brief comparison of the various memory allocation methods:

CoTaskMemAlloc

GlobalAlloc

HeapAlloc

LocalAlloc

mallo

new

VirtualAlloc

Although the GlobalAlloc, LocalAlloc, and HeapAlloc functions ultimately allocate memory

from the same heap, each provides a different set of functionality. For example, HeapAlloc can

be instructed to raise an exception if memory could not be allocated, a capability not available


with LocalAlloc. LocalAlloc supports allocation of handles which permit the underlying memory

to be moved by a reallocation without changing the handle value, a capability not available with

HeapAlloc.

Starting with 32-bit Windows, GlobalAlloc and LocalAlloc are implemented as wrapper

functions that call HeapAllocusing a handle to the process's default heap. Therefore, GlobalAlloc

and LocalAlloc have greater overhead thanHeapAlloc.

Because the different heap allocators provide distinctive functionality by using different

mechanisms, you must free memory with the correct function. For example, memory allocated

with HeapAlloc must be freed with HeapFree and notLocalFree or GlobalFree. Memory

allocated with GlobalAlloc or LocalAlloc must be queried, validated, and released

with the corresponding global or local function. The VirtualAllo However, its allocations use a

page granularity, so using VirtualAlloc can result in higher memory usag.The malloc function

has the disadvantage of being run-time dependent. The new operator has the disadvantage of

being compiler dependent and language dependent.User memory can be allocated according to

several schemes,virtual memory, memory-mapped les, heaps,

and thread-local storage.

Windows 7 provides a technique to check the memory allocation and de allocation for the

processes and killing and creating a new process in Task Manager. When an active process is in

memory and the system runs out of memory to allocate, does it deny the creation of a new

process or does it use a swap file.


Segmentation

Memory segmentation is the division of a computer's primary memory into segments or

sections. In a computer system using segmentation, a reference to a memory location includes a

value that identifies a segment and an within that segment only. Segments or sections are also

used in object files of compiled programs when they are linked together into a program image

and when the image is loaded into memory.

Segments usually correspond to natural divisions of a program such as individual routines or data

tables so segmentation is generally more visible to the programmer than paging alone.

Swap file

Swap file is a space on a hard disk used as the virtual memory extension of a computer's real

memory (RAM). A swap file allows your computer's operating system to pretend that you have

more RAM than you actually what we do. The last recently used files in RAM can be "swapped

out" to your hard disk until they are needed later so that new files can be "swapped in" to RAM

In larger operating systems , the units that are moved are called pages and the swapping is called

paging One advantage of a swap file is that it can be organized as a single contiguous space so

that fewer I/O operations are required to read or write a complete file.

.

MEMORY MAPPING

A memory map is a structure of data that indicates how memory is laid out. Memory

maps can have a different meaning in different parts of the operating system.In the boot process,


a memory map is passed on from the firmware in order to instruct an operating system kernel

about memory layout. It contains the information regarding the size of total memory, any

reserved regions and may also provide other details specific to the architecture.

Virtual memory allows the system to use hard disk space to store information normally stored in

RAM. Windows 7 and Windows Vista manages virtual memory by using a paging file. You

specify the minimum and maximum size of this file. If the size is different from the default in

Windows.Vista, applications may return errors.Dynamically monitor memory for a few minutes

to see the hard fault count increase quickly.A page table is the data structure used by the

Windows Virtual Memory Manager (VMM) to store the mapping between virtual addresses and

physical addresses in memory. The performance counter Free System Page Table Entries is the

number of page table entries not currently used by the system.

The primary benefit of memory mapping a file is increasing I/O performance, especially when

used on large files. Since Windows 95, Windows-based operating systems have used a special

file that acts as a sort of "scratch pad" to store modified pages that are still in use by some

process.

Page file space is reserved when the pages are initially committed, however the page file

locations are not chosen until the page is written to disk. So, in simplistic terms, the page file is

used by Windows to hold temporary data which is swapped in and out of physical memory in

order to provide a larger virtual memory set.


Page file

The page file is one of those pieces of the operating system that administrators know t when hat

they need to have - but they can't always explain why they need it, or how to accurately size it.

Operating System

The memory management function keeps track of the status of each memory location,

either allocated

It determines how memory is allocated among competing processes, deciding who gets

memory, when they receive it, and how much they are allowed.

When memory is allocated it determines which memory locations will be assigned. It

tracks when memory is freed and updates the status.

Conclusion :

Research on Memory management and virtual memory have been studied and presented.

References

Operating Systems Design and Implementation by Andrew S. Tannenbaum, Albert S.

Woodhull, Alfred Woodhull

Simple Memory Allocation Algorithms (originally published on OSDEV Community)

Formal Description of Components in Operating Systems written by Asen Petkov Iliev


http://galvin.info/history-of-operating-system-concepts-textbook/.

Berger, E.D.; Zorn, B.G.; McKinley, K.S. (2001). "composing high perfomence memory

allocation"

Jessen, Elke (2004). "Origin of the Virtual Memory Concept".

CS554BH1 OPERATING SYSTEM MEMORY MANAGEMENT AND VIRTUAL MEMORY

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