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The term memory can be defined as a collection of data in a specific format. It is used to store instructions and process data. The memory comprises a large array or group of words or bytes, each with its own location. The primary purpose of a computer system is to execute programs. These programs, along with the information they access, should be in the main memory during execution. The CPU fetches instructions from memory according to the value of the program counter.
To achieve a degree of multiprogramming and proper utilization of memory, memory management is important. Many memory management methods exist, reflecting various approaches, and the effectiveness of each algorithm depends on the situation.
Here, we will cover the following memory management topics:
- What is Main Memory?
- What is Memory Management?
- Why Memory Management is Required?
- Logical Address Space and Physical Address Space
- Static and Dynamic Loading
- Static and Dynamic Linking
- Swapping
- Contiguous Memory Allocation
- Memory Allocation
- First Fit
- Best Fit
- Worst Fit
Before we start Memory management, let us know what is main memory is.
What is Main Memory?The main memory is central to the operation of a Modern Computer. Main Memory is a large array of words or bytes, ranging in size from...
- Static Loading: Static Loading is basically loading the entire program into a fixed address. It requires more memory space.
- Dynamic Loading: The entire program and all data of a process must be in physical memory for the process to execute. So, the size of a process is limited to the size of physical memory. To gain proper memory utilization, dynamic loading is used. In dynamic loading, a routine is not loaded until it is called. All routines are residing on disk in a relocatable load format. One of the advantages of dynamic loading is that the unused routine is never loaded. This loading is useful when a large amount of code is needed to handle it efficiently.
- Static Linking: In static linking, the linker combines all necessary program modules into a single executable program. So there is no runtime dependency. Some operating systems support only static linking, in which system language libraries are treated like any other object module.
- Dynamic Linking: The basic concept of dynamic linking is similar to dynamic loading. In dynamic linking, “Stub” is included for each appropriate library routine reference. A stub is a small piece of code. When the stub is executed, it checks whether the needed routine is already in memory or not. If not available then the program loads the routine into memory.
- One part of the operating system
- The second part of the user program
- Multiple partition allocation: In this method, a process is selected from the input queue and loaded into the free partition. When the process terminates, the partition becomes available for other processes.
- Fixed partition allocation: In this method, the operating system maintains a table that indicates which parts of memory are available and which are occupied by processes. Initially, all memory is available for user processes and is considered one large block of available memory. This available memory is known as a “Hole”. When the process arrives and needs memory, we search for a hole that is large enough to store this process. If the requirement is fulfilled then we allocate memory to process, otherwise keeping the rest available to satisfy future requests. While allocating a memory sometimes dynamic storage allocation problems occur, which concerns how to satisfy a request of size n from a list of free holes. There are some solutions to this problem:
- Internal fragmentation: Internal fragmentation occurs when memory blocks are allocated to the process more than their requested size. Due to this some unused space is left over and creating an internal fragmentation problem.Example: Suppose there is a fixed partitioning used for memory allocation and the different sizes of blocks 3MB, 6MB, and 7MB space in memory. Now a new process p4 of size 2MB comes and demands a block of memory. It gets a memory block of 3MB but 1MB block of memory is a waste, and it can not be allocated to other processes too. This is called internal fragmentation.
- External fragmentation: In External Fragmentation, we have a free memory block, but we can not assign it to a process because blocks are not contiguous. Example: Suppose (consider the above example) three processes p1, p2, and p3 come with sizes 2MB, 4MB, and 7MB respectively. Now they get memory blocks of size 3MB, 6MB, and 7MB allocated respectively. After allocating the process p1 process and the p2 process left 1MB and 2MB. Suppose a new process p4 comes and demands a 3MB block of memory, which is available, but we can not assign it because free memory space is not contiguous. This is called external fragmentation.
- Logical Address or Virtual Address (represented in bits): An address generated by the CPU.
- Logical Address Space or Virtual Address Space (represented in words or bytes): The set of all logical addresses generated by a program.
- Physical Address (represented in bits): An address actually available on a memory unit.
- Physical Address Space (represented in words or bytes): The set of all physical addresses corresponding to the logical addresses.
- If Logical Address = 31 bits, then Logical Address Space = 231 words = 2 G words (1 G = 230)
- If Logical Address Space = 128 M words = 27 * 220 words, then Logical Address = log2 227 = 27 bits
- If Physical Address = 22 bits, then Physical Address Space = 222 words = 4 M words (1 M = 220)
- If Physical Address Space = 16 M words = 24 * 220 words, then Physical Address = log2 224 = 24 bits
- The Physical Address Space is conceptually divided into several fixed-size blocks, called frames.
- The Logical Address Space is also split into fixed-size blocks, called pages.
- Page Size = Frame Size
- Physical Address = 12 bits, then Physical Address Space = 4 K words
- Logical Address = 13 bits, then Logical Address Space = 8 K words
- Page size = frame size = 1 K words (assumption)
- Page Number(p): Number of bits required to represent the pages in Logical Address Space or Page number
- Page Offset(d): Number of bits required to represent a particular word in a page or page size of Logical Address Space or word number of a page or page offset.
- Frame Number(f): Number of bits required to represent the frame of Physical Address Space or Frame number frame
- Frame Offset(d): Number of bits required to represent a particular word in a frame or frame size of Physical Address Space or word number of a frame or frame offset.
- The TLB is an associative, high-speed memory.
- Each entry in TLB consists of two parts: a tag and a value.
- When this memory is used, then an item is compared with all tags simultaneously. If the item is found, then the corresponding value is returned.
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The term memory can be defined as a collection of data in a specific format. It is used to store instructions and process data. The memory comprises a large array or group of words or bytes, each with its own location. The primary purpose of a computer system is to execute programs. These programs, along with the information they access, should be in the main memory during execution. The CPU fetches instructions from memory according to the value of the program counter.
To achieve a degree of multiprogramming and proper utilization of memory, memory management is important. Many memory management methods exist, reflecting various approaches, and the effectiveness of each algorithm depends on the situation.
Here, we will cover the following memory management topics:
- What is Main Memory?
- What is Memory Management?
- Why Memory Management is Required?
- Logical Address Space and Physical Address Space
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Top Answer
Answered Jul 25, 2021 · 1 votes
Where does the MMU fit what does it do since the address translation and page-in / page out is done by CPU and OS?
The MMU is part of a modern CPU. The virtual to physical address translation is done by the MMU / CPU hardware.
The Operating System kernel (software) is responsible for making sure that that the MMU is correctly configured (so that the correct pages are mapped into user-space processes address spaces), and for handling the page fault interrupts generated by the MMU. It also deals with the higher level functions such as:
- swapping pages in and out,
- keeping track of which pages are clean,
- ensuring that there is a pool of clean pages that can be evicted if there is a page fault,
- dealing with scheduling issues such as killing processes that are causing thrashing
- and so on.
How is the Virtual address space assign in interpreted lang?
It is the same as for a non-interpreted programming language. In the interpreted case, the interpreter is a user-space (non-privileged) program. The code that it is interpreting is ... data for the interpreter.
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The term memory can be defined as a collection of data in a specific format. It is used to store instructions and process data. The memory comprises a large array or group of words or bytes, each with its own location. The primary purpose of a computer system is to execute programs. These programs, along with the information they access, should be in the main memory during execution. The CPU fetches instructions from memory according to the value of the program counter.
To achieve a degree of multiprogramming and proper utilization of memory, memory management is important. Many memory management methods exist, reflecting various approaches, and the effectiveness of each algorithm depends on the situation.
Here, we will cover the following memory management topics:
- What is Main Memory?
- What is Memory Management?
- Why Memory Management is Required?
- Logical Address Space and Physical Address Space
- Static and Dynamic Loading
- Static and Dynamic Linking
- Swapping
- Contiguous Memory Allocation
- Memory Allocation
- First Fit
- Best Fit
- Worst Fit
Before we start Memory management, let us know what is main memory is.
What is Main Memory?The main memory is central to the operation of a Modern Computer. Main Memory is a large array of words or bytes, ranging in size from...
- Static Loading: Static Loading is basically loading the entire program into a fixed address. It requires more memory space.
- Dynamic Loading: The entire program and all data of a process must be in physical memory for the process to execute. So, the size of a process is limited to the size of physical memory. To gain proper memory utilization, dynamic loading is used. In dynamic loading, a routine is not loaded until it is called. All routines are residing on disk in a relocatable load format. One of the advantages of dynamic loading is that the unused routine is never loaded. This loading is useful when a large amount of code is needed to handle it efficiently.
- Static Linking: In static linking, the linker combines all necessary program modules into a single executable program. So there is no runtime dependency. Some operating systems support only static linking, in which system language libraries are treated like any other object module.
- Dynamic Linking: The basic concept of dynamic linking is similar to dynamic loading. In dynamic linking, “Stub” is included for each appropriate library routine reference. A stub is a small piece of code. When the stub is executed, it checks whether the needed routine is already in memory or not. If not available then the program loads the routine into memory.
- One part of the operating system
- The second part of the user program
- Multiple partition allocation: In this method, a process is selected from the input queue and loaded into the free partition. When the process terminates, the partition becomes available for other processes.
- Fixed partition allocation: In this method, the operating system maintains a table that indicates which parts of memory are available and which are occupied by processes. Initially, all memory is available for user processes and is considered one large block of available memory. This available memory is known as a “Hole”. When the process arrives and needs memory, we search for a hole that is large enough to store this process. If the requirement is fulfilled then we allocate memory to process, otherwise keeping the rest available to satisfy future requests. While allocating a memory sometimes dynamic storage allocation problems occur, which concerns how to satisfy a request of size n from a list of free holes. There are some solutions to this problem:
- Internal fragmentation: Internal fragmentation occurs when memory blocks are allocated to the process more than their requested size. Due to this some unused space is left over and creating an internal fragmentation problem.Example: Suppose there is a fixed partitioning used for memory allocation and the different sizes of blocks 3MB, 6MB, and 7MB space in memory. Now a new process p4 of size 2MB comes and demands a block of memory. It gets a memory block of 3MB but 1MB block of memory is a waste, and it can not be allocated to other processes too. This is called internal fragmentation.
- External fragmentation: In External Fragmentation, we have a free memory block, but we can not assign it to a process because blocks are not contiguous. Example: Suppose (consider the above example) three processes p1, p2, and p3 come with sizes 2MB, 4MB, and 7MB respectively. Now they get memory blocks of size 3MB, 6MB, and 7MB allocated respectively. After allocating the process p1 process and the p2 process left 1MB and 2MB. Suppose a new process p4 comes and demands a 3MB block of memory, which is available, but we can not assign it because free memory space is not contiguous. This is called external fragmentation.
- Logical Address or Virtual Address (represented in bits): An address generated by the CPU.
- Logical Address Space or Virtual Address Space (represented in words or bytes): The set of all logical addresses generated by a program.
- Physical Address (represented in bits): An address actually available on a memory unit.
- Physical Address Space (represented in words or bytes): The set of all physical addresses corresponding to the logical addresses.
- If Logical Address = 31 bits, then Logical Address Space = 231 words = 2 G words (1 G = 230)
- If Logical Address Space = 128 M words = 27 * 220 words, then Logical Address = log2 227 = 27 bits
- If Physical Address = 22 bits, then Physical Address Space = 222 words = 4 M words (1 M = 220)
- If Physical Address Space = 16 M words = 24 * 220 words, then Physical Address = log2 224 = 24 bits
- The Physical Address Space is conceptually divided into several fixed-size blocks, called frames.
- The Logical Address Space is also split into fixed-size blocks, called pages.
- Page Size = Frame Size
- Physical Address = 12 bits, then Physical Address Space = 4 K words
- Logical Address = 13 bits, then Logical Address Space = 8 K words
- Page size = frame size = 1 K words (assumption)
- Page Number(p): Number of bits required to represent the pages in Logical Address Space or Page number
- Page Offset(d): Number of bits required to represent a particular word in a page or page size of Logical Address Space or word number of a page or page offset.
- Frame Number(f): Number of bits required to represent the frame of Physical Address Space or Frame number frame
- Frame Offset(d): Number of bits required to represent a particular word in a frame or frame size of Physical Address Space or word number of a frame or frame offset.
- The TLB is an associative, high-speed memory.
- Each entry in TLB consists of two parts: a tag and a value.
- When this memory is used, then an item is compared with all tags simultaneously. If the item is found, then the corresponding value is returned.
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www.geeksforgeeks.org › memory-management-inMemory Management in Operating System - GeeksforGeeks
www.geeksforgeeks.org › memory-management-inSep 6, 2023 · Learn the basics of memory management, such as main memory, logical and physical address space, static and dynamic loading and linking, swapping, and memory allocation methods. Explore the advantages and disadvantages of different memory management approaches with examples and diagrams.
- 24 min
phoenixnap.com › kb › memory-managementMemory Management in Operating Systems Explained - phoenixNAP
phoenixnap.com › kb › memory-managementSep 22, 2023 · Learn how memory management enables running multiple processes simultaneously without interruptions. Understand key concepts, mechanisms, and techniques such as memory addresses, loading, linking, swapping, and fragmentation.
www.guru99.com › os-memory-managementMemory Management in OS: Contiguous, Swapping, Fragmentation
www.guru99.com › os-memory-managementFeb 3, 2024 · Learn what memory management is, why it is important, and how it works in operating systems. Explore various memory management techniques such as contiguous, partition, paged, segmented, swapping, and more with examples and diagrams.
www.tutorialspoint.com › operating_system › os_memoryOperating System - Memory Management - Online Tutorials Library
www.tutorialspoint.com › operating_system › os_memoryLearn the basic concepts of memory management in operating systems, such as process address space, static and dynamic loading, swapping, memory allocation, fragmentation and paging. This tutorial covers the theory and examples of memory management techniques and mechanisms.
en.wikipedia.org › wiki › Memory_managementMemory management (operating systems) - Wikipedia
en.wikipedia.org › wiki › Memory_managementIn operating systems, memory management is the function responsible for managing the computer's primary memory. [1] : 105–208. The memory management function keeps track of the status of each memory location, either allocated or free. It determines how memory is allocated among competing processes, deciding which gets memory, when they ...
technobyte.org › memory-management-os-simpleMemory Management in Operating Systems - Simple Explanation
technobyte.org › memory-management-os-simpleApr 23, 2024 · Learn the basics of memory management in OS, such as memory hierarchy, memory manager, memory partitioning, fragmentation, and swapping. Explore different memory management techniques, such as bitmap, linked list, paging, segmentation, and virtual memory.
People also ask
What is memory management in operating systems?
- Memory management is a vital and complex operating system task. It enables running multiple processes simultaneously without interruptions. Knowing how memory management in operating systems works is crucial for system stability and improving system performance. This article explains key concepts of memory management in operating systems.
Memory Management in Operating Systems Explained - phoenixNAP
phoenixnap.com/kb/memory-managementWhat is memory management in a multiprogramming computer?
- In a multiprogramming computer, the Operating System resides in a part of memory, and the rest is used by multiple processes. The task of subdividing the memory among different processes is called Memory Management. Memory management is a method in the operating system to manage operations between main memory and disk during process execution.
Memory Management in Operating System - GeeksforGeeks
www.geeksforgeeks.org/memory-management-in-operating-system/What is memory management in Linux?
- The task of subdividing the memory among different processes is called Memory Management. Memory management is a method in the operating system to manage operations between main memory and disk during process execution. The main aim of memory management is to achieve efficient utilization of memory. Why Memory Management is Required?
Memory Management in Operating System - GeeksforGeeks
www.geeksforgeeks.org/memory-management-in-operating-system/generalscience.io › os › chaptersGeneral Science - Memory Management in Operating Systems
generalscience.io › os › chaptersLearn the fundamental concepts and techniques of memory management, such as paging, segmentation, allocation, protection, and garbage collection. Explore the challenges and trade-offs of memory management in modern operating systems.
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