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What is the main goal of memory management in operating systems?
What is the main goal of memory management in operating systems?
The main goal of memory management is to allow multiple processes to share the CPU and physical memory efficiently and securely.
What is the difference between a logical address and a physical address?
What is the difference between a logical address and a physical address?
In compile-time and load-time address-binding schemes, logical and physical addresses are always the same.
In compile-time and load-time address-binding schemes, logical and physical addresses are always the same.
True
What are the three main stages where binding of logical to physical addresses can occur?
What are the three main stages where binding of logical to physical addresses can occur?
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What does 'relocatable' mean in the context of memory management?
What does 'relocatable' mean in the context of memory management?
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What is the general purpose of the 'mapping' process in memory management?
What is the general purpose of the 'mapping' process in memory management?
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What are the advantages of using a 'dynamic relocation' scheme?
What are the advantages of using a 'dynamic relocation' scheme?
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Describe the concept of a resident monitor in memory management.
Describe the concept of a resident monitor in memory management.
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What is the primary advantage of using a single-partition allocation scheme?
What is the primary advantage of using a single-partition allocation scheme?
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In single-partition allocation, user programs are prevented from accessing memory outside their allotted partition.
In single-partition allocation, user programs are prevented from accessing memory outside their allotted partition.
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Explain the concept of 'internal fragmentation' in the context of contiguous memory allocation.
Explain the concept of 'internal fragmentation' in the context of contiguous memory allocation.
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Which memory allocation strategy is known for being the fastest but potentially leading to more memory fragmentation?
Which memory allocation strategy is known for being the fastest but potentially leading to more memory fragmentation?
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The 'buddy system' memory allocation method primarily aims to reduce external fragmentation by merging free adjacent blocks of memory.
The 'buddy system' memory allocation method primarily aims to reduce external fragmentation by merging free adjacent blocks of memory.
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What are the two main challenges associated with using contiguous memory allocation?
What are the two main challenges associated with using contiguous memory allocation?
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What is the main advantage of using paging in memory management?
What is the main advantage of using paging in memory management?
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What are the two primary components of a logical address in paging?
What are the two primary components of a logical address in paging?
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What is the main purpose of the page table in paging?
What is the main purpose of the page table in paging?
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Internal fragmentation is a common problem associated with paging.
Internal fragmentation is a common problem associated with paging.
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What is the primary role of the Translation Lookaside Buffer (TLB) in paging?
What is the primary role of the Translation Lookaside Buffer (TLB) in paging?
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What are the two main ways in which the TLB can be implemented?
What are the two main ways in which the TLB can be implemented?
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Describe the concept of 'shared pages' in memory management.
Describe the concept of 'shared pages' in memory management.
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The use of shared pages typically requires that the shared pages be marked as 'write protected' to avoid conflicts while multiple processes are accessing them.
The use of shared pages typically requires that the shared pages be marked as 'write protected' to avoid conflicts while multiple processes are accessing them.
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Explain the concept of an 'inverted page table' and its main advantage.
Explain the concept of an 'inverted page table' and its main advantage.
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Why is the concept of 'address mapping' crucial in memory management?
Why is the concept of 'address mapping' crucial in memory management?
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Which memory management technique is used for handling large address spaces by dividing the page table into multiple hierarchies?
Which memory management technique is used for handling large address spaces by dividing the page table into multiple hierarchies?
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What is the main difference between paging and segmentation?
What is the main difference between paging and segmentation?
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Explain the concept of 'paged segmentation' in memory management.
Explain the concept of 'paged segmentation' in memory management.
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Paged segmentation is a commonly used technique in modern operating systems due to its ability to handle large virtual address spaces while offering flexible memory allocation.
Paged segmentation is a commonly used technique in modern operating systems due to its ability to handle large virtual address spaces while offering flexible memory allocation.
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What is the main goal of compaction in contiguous memory allocation?
What is the main goal of compaction in contiguous memory allocation?
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Compaction is always a practical solution for handling external fragmentation in memory management.
Compaction is always a practical solution for handling external fragmentation in memory management.
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What is the principle behind 'swapping' in memory management?
What is the principle behind 'swapping' in memory management?
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Swapping is a more efficient technique compared to compaction for handling memory fragmentation.
Swapping is a more efficient technique compared to compaction for handling memory fragmentation.
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What is the primary purpose of operating system memory management?
What is the primary purpose of operating system memory management?
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Study Notes
Operating Systems - Memory Management
- Memory management is the process of sharing physical memory among different processes.
- Processes share the CPU and physical memory.
- Calculating effective addresses involves fetching from the instruction and using index offsets.
- Logical addresses are generated by the CPU (also called virtual addresses).
- Physical addresses are seen by the memory unit.
- Compile-time and load-time address-binding schemes use the same logical and physical addresses.
- Execution-time address-binding schemes use different logical and physical addresses.
Relocatable Binding
- The program image can reside anywhere in physical memory.
- Programs need real memory to reside in.
- Mapping logical to physical addresses is called relocation.
- Relocation can happen at compile/link time.
- Symbolic addresses are converted to relocatable addresses.
- Relocatable code is produced if the program's location is not known in advance.
Binding Logical to Physical
- Binding can be done at compile/link time, load time, or run time.
- Relocatable code is bound to physical addresses at load time.
- Addressing during runtime allows flexibility in virtual memory mapping.
- A compiler and linker work together to determine effective addresses, which are then used by the loader.
Memory Management - Binding Logical To Physical
- Data used within compiled source is offset within the object module.
- Binding can be at compile time, load time, or run time.
- Program execution allows the code to be moved around.
Memory Management - Definitions
- The concept of a logical address space bound to a separate physical address space is central to proper memory management.
- Logical address
- Virtual address
- Physical address
- Logical and physical addresses are the same in compile-time/load-time schemes but differ at execution time.
Memory Management - Dynamic Loading
- Routine is not loaded until it is needed.
- Better memory utilization because unused routines are not loaded.
- Useful for infrequent, large amounts of code.
Memory Management - Dynamic Linking
- Linking happens at execution time.
- A small piece of code, a stub, finds an appropriate routine in a library to be executed.
- The stub replaces itself with the routine's address.
- The operating system checks whether the routine is in the processes' memory space before executing it.
Memory Management - Dynamic Storage/Contiguous Allocation
- Memory is divided into fixed-sized regions.
- The number of partitions dictates the level of multiprogramming.
- Each partition holds a given process during its runtime.
- Protection is around partitions with bounds (upper, lower) and base/limit.
Memory Management - Resident Monitor
- Primitive Operating System.
- Typically found in low memory where interrupt vectors are located.
- Checks memory references against a fence (fixed or variable).
- User code can be placed in memory starting at a fence and has a fixed execution location.
- The system can be run from a high address and shift back to a lower location.
- A base register for user address adjustments is added.
- Users are isolated from physical addresses using logical addresses.
Memory Management - Paging
- A logical address space can be noncontiguous.
- Physical memory is divided into fixed-sized blocks - frames.
- Logical memory is divided into blocks of the same size - pages.
- A page table translates logical addresses to physical addresses.
- Internal fragmentation can occur.
Memory Management - Addressing Translation
- The CPU divides a generated address into page number (p) and page offset (d).
- Page number (p) is used to index into a page table.
- The page table contains the base address of the page in physical memory.
- The page offset (d) is used with the base address to determine the physical memory address.
Memory Management - Hardware and Page Table
- Hardware determines the size of frames and pages.
- Hardware maps a page number and an offset to a physical memory location.
Memory Management - Paging Example
- Paging can be illustrated with an example using a 32-byte memory with 4-byte pages.
- A page table is created that maps logical addresses to physical memory addresses.
Memory Management - Paging Implementation and TLB
- A translation look-aside buffer (TLB) is used so that physical address lookups from the page table are faster.
- The TLB is a special cache that holds frequently used page table entries.
- A TLB hit is very fast and only a few registers are used for TLB lookups.
Memory Management - Implementation of the Page Table
- The hit rate for the TLB is between 90 and 98%.
- The TLB has 100 registers for storing page table entries.
Memory Management - Shared Pages
- Pages are shared among multiple processes.
- Pages can be read-only in some contexts.
Memory Management - Protection and Sharing
- Bits are associated with page tables to allow for read, write, and execute permissions.
- A valid bit indicates whether a page is within the address space.
Memory Management - Address Mapping
- Physical memory can be larger than logical memory.
- The operating system maintains a frame describing physical pages and their process associations.
Memory Management - Multilevel Page Table
- This can be used for large address spaces.
- The logical address is p1, p2, and d; where 2 levels of page tables are used.
Memory Management - Segmentation
- Programmers view a process as a series of unordered segments.
- The use of segment names makes it easier to locate pieces of memory.
- Logical address = segment name + offset.
Memory Management - Segmentation - Hardware
- Hardware maps a dyad (segment/offset) into a one-dimensional address.
Memory Management - Segmentation - Protection and Sharing
- Addresses are associated with logical units.
- Bounds checking can be applied to array segments.
- Segments can be marked as shareable.
Memory Management - Segmentation - Fragmentation
- Variables in segment lengths lead to fragmentation.
Memory Management - Segmented Paging
- Combination of segmentation and paging.
- Logical addresses have a descriptor table, linear address has directory page and offset.
Memory Management - Wrap-up
- Paging involves associating logical addresses with physical memory addresses.
- This is a very important aspect of modern operating systems.
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Description
Test your knowledge on memory management in operating systems with this quiz. Covering topics like logical and physical addresses, address binding schemes, and relocatable binding, you'll assess your understanding of how processes share memory. Perfect for students studying operating systems.
