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What is a primary purpose of memory management in an operating system?
What is a primary purpose of memory management in an operating system?
Which system component directly interfaces with memory and registers?
Which system component directly interfaces with memory and registers?
In memory architecture, what is the role of cache memory?
In memory architecture, what is the role of cache memory?
What is one of the challenges posed by the use of main memory?
What is one of the challenges posed by the use of main memory?
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What does the term 'contiguous memory allocation' refer to?
What does the term 'contiguous memory allocation' refer to?
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What is the calculation for internal fragmentation when a process size is 72,766 bytes and uses a page size of 2,048 bytes?
What is the calculation for internal fragmentation when a process size is 72,766 bytes and uses a page size of 2,048 bytes?
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Why are smaller frame sizes generally considered desirable?
Why are smaller frame sizes generally considered desirable?
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What does the page-table length register (PTLR) indicate?
What does the page-table length register (PTLR) indicate?
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What is the role of the translation lookaside buffer (TLB) in a paging system?
What is the role of the translation lookaside buffer (TLB) in a paging system?
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What is the worst-case fragmentation scenario in a paging system?
What is the worst-case fragmentation scenario in a paging system?
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What is the primary function of the Memory-Management Unit (MMU)?
What is the primary function of the Memory-Management Unit (MMU)?
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How does the logical address differ from the physical address during execution-time binding?
How does the logical address differ from the physical address during execution-time binding?
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What happens when a user process generates an address?
What happens when a user process generates an address?
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In which address-binding scheme are logical and physical addresses equivalent?
In which address-binding scheme are logical and physical addresses equivalent?
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Which statement is true about logical address space?
Which statement is true about logical address space?
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What is the role of the relocation register in memory management?
What is the role of the relocation register in memory management?
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Which of the following best describes the physical address space?
Which of the following best describes the physical address space?
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Which statement best describes logical addresses?
Which statement best describes logical addresses?
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What is the purpose of the relocation register in a computer system?
What is the purpose of the relocation register in a computer system?
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What advantage does dynamic loading provide in memory management?
What advantage does dynamic loading provide in memory management?
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Which characteristic defines dynamic linking as opposed to static linking?
Which characteristic defines dynamic linking as opposed to static linking?
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In contiguous allocation, what is the role of the limit register?
In contiguous allocation, what is the role of the limit register?
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How does the operating system maintain efficient memory allocation in a variable partition system?
How does the operating system maintain efficient memory allocation in a variable partition system?
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What is a characteristic of a hole in the context of variable partition allocation?
What is a characteristic of a hole in the context of variable partition allocation?
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What occurs when a process exits in a variable-partition system?
What occurs when a process exits in a variable-partition system?
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Which of the following statements about dynamic storage-allocation problem is true?
Which of the following statements about dynamic storage-allocation problem is true?
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What role does the stub play in the dynamic linking process?
What role does the stub play in the dynamic linking process?
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Which of the following is true about memory management through contiguous allocation?
Which of the following is true about memory management through contiguous allocation?
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What is the purpose of the TLB in the context of virtual memory management?
What is the purpose of the TLB in the context of virtual memory management?
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Which statement accurately describes the functionality of the hash tables in the inverted page table architecture?
Which statement accurately describes the functionality of the hash tables in the inverted page table architecture?
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What happens when a virtual address reference results in a TLB miss?
What happens when a virtual address reference results in a TLB miss?
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What structural components make up the inverted page table architecture in the Oracle SPARC Solaris?
What structural components make up the inverted page table architecture in the Oracle SPARC Solaris?
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What role does the translation storage buffer (TSB) play in the memory address translation process?
What role does the translation storage buffer (TSB) play in the memory address translation process?
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What does an entry in the hash table for virtual memory translate to?
What does an entry in the hash table for virtual memory translate to?
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What is the main goal of the architecture used in modern, tightly integrated hardware operating systems?
What is the main goal of the architecture used in modern, tightly integrated hardware operating systems?
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In the case of a TLB hit, what is the result of the lookup?
In the case of a TLB hit, what is the result of the lookup?
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What is a condition that typically triggers the process of swapping in an operating system?
What is a condition that typically triggers the process of swapping in an operating system?
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How can context switch time be affected by swapping?
How can context switch time be affected by swapping?
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Which of the following methods do mobile operating systems typically use to manage low memory instead of swapping?
Which of the following methods do mobile operating systems typically use to manage low memory instead of swapping?
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What can happen if a process is swapped out while pending I/O operations are occurring?
What can happen if a process is swapped out while pending I/O operations are occurring?
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What does Intel's Page Address Extension (PAE) allow 32-bit applications to do?
What does Intel's Page Address Extension (PAE) allow 32-bit applications to do?
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What is a common memory management method supported by both iOS and Android?
What is a common memory management method supported by both iOS and Android?
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In the Intel IA-32 architecture, how many segments can a process have?
In the Intel IA-32 architecture, how many segments can a process have?
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Which component primarily handles the translation of logical addresses to physical addresses in the IA-32 architecture?
Which component primarily handles the translation of logical addresses to physical addresses in the IA-32 architecture?
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What is a characteristic of modern operating systems regarding standard swapping?
What is a characteristic of modern operating systems regarding standard swapping?
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In the context of context switch time, what is one method to potentially reduce the swapping component time?
In the context of context switch time, what is one method to potentially reduce the swapping component time?
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What is the practical limit of addressing implemented in contemporary Intel x86-64 systems?
What is the practical limit of addressing implemented in contemporary Intel x86-64 systems?
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What major advantage does a two-level translation lookaside buffer (TLB) provide in the ARM architecture?
What major advantage does a two-level translation lookaside buffer (TLB) provide in the ARM architecture?
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What is the primary storage problem for mobile systems that limits their use of swapping?
What is the primary storage problem for mobile systems that limits their use of swapping?
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Study Notes
Main Memory
- Main memory supports both operating system and user processes
- Memory is a limited resource, so efficient allocation is crucial
- Contiguous allocation is one early approach
- Memory is divided into partitions: resident OS (low memory, interrupt vector), user processes (high memory)
- Each process is in its own contiguous section
Protection
- Processes need protection from each other and the OS
- Base and limit registers define a process' logical address space
- The CPU checks every memory access to ensure it's within the base/limit range
- Instructions to load those registers are usually privileged
Address Binding
- Programs can be bound to memory addresses at different stages: compile time, load time, or execution time
- Compile time: Addresses known at compile time.
- Load time: Addresses known at load time.
- Execution time: Addresses are determined at run time.
- Binding methods map symbolic addresses to absolute addresses
Multistep Processing
- Source program/code is first compiled, or assembled
- Then object modules are written
- Object modules are linked together
- The resulting executable load module is loaded by the loader
Logical vs Physical Address Space
- Logical (virtual) address is generated by the CPU
- Physical address is used by the memory unit
- In compile-time and load-time, the logical and physical addresses are the same.
- They differ in execution time.
- Logical address space is the set of all logical addresses generated by a program.
- Physical address space is the set of all physical addresses generated by a program
Memory-Management Unit (MMU)
- Hardware that maps logical to physical addresses at runtime
- This is a generalization of the base-register scheme (the relocation register)
- Used to protect user processes from each other
Dynamic Loading
- The entire program isn't loaded into memory at once
- Routines loaded only when needed
- Improves memory usage
Dynamic Linking
- Linking of libraries is postponed until execution time
- Uses stubs to locate routines
- Implementation of shared libraries
Contiguous Allocation (cont.)
- Relocation registers needed to protect user processes from each other and from changing operating system code/data
- Base register contains smallest physical address
- Limit register contains the range of logical addresses
- Allows for dynamic mapping of logical to physical addresses
Variable Partition
- Multiple partitions of variable sizes
- Holds OS and user programs
- Free memory areas (holes)
- The OS maintains a record of free blocks of memory
Dynamic Storage Allocation
- Methods (First-fit, best-fit, worst-fit) to satisfy requests for memory allocation sized 'n' bytes
- First-fit: fastest, but doesn't necessarily minimize leftover space
- Best-fit: minimizes leftover space, but slowest.
- Worst-fit: allocates the largest hole, producing the largest leftover hole.
Fragmentation
- External fragmentation: Memory space exists, but it is not contiguous.
- Internal fragmentation: Assigned memory is larger than needed.
- Compaction: Attempts to reduce external fragmentation by moving memory blocks
Paging
- Physical address space of a process can be noncontiguous
- Improves external fragmentation
- Divides physical memory into fixed-sized blocks
- Divides logical memory into blocks of same size
Address Translation
- CPU-generated address divided into page number and page offset
- Page number is used as an index to a page table
- Page offset is combined with the base address to define the physical memory address
Paging Hardware
- Logical to physical address mapping
- Page table hardware
Paging Model
- Logical memory and physical memory are divided into pages
- Logical page number corresponds to a specific physical frame
Paging Example
- Showcases logical and physical address mapping with page table lookup
Paging - Calculating internal fragmentation
- Calculates internal memory wasted due to paging.
Free Frames
- Free frames stored in a free-frame list
- Allocation occurs using the free-frame list
- Free frames are added back to free-frame list upon deallocation
Implementation of Page Table
- Page table kept in main memory
- Page-table base register (PTBR) and length register (PTLR)
Translation Look-Aside Buffer (TLB)
- Special fast-lookup hardware cache
- Maps logical to physical addresses
Hardware
- Associative memory is used for parallel search
- Address translation uses page number and the associative register
- Page number in register, frame number returned
- Otherwise, search in memory page table
Paging Hardware with TLB
- A diagram showing the steps involved in the TLB lookup
Effective Access Time
- Calculating effective access time considering hit ratio.
Memory Protection
- Mechanisms used for memory protection
- Valid-invalid bit in the page table
Valid or Invalid Bit
- Valid: indicates the page is in the process' logical address space
- Invalid: indicates the page isn't in process' logical address space
Shared Pages
- One copy of read-only code shared amongst multiple processes
- Improves efficiency and reduces memory usage
- Multiple processes can access the shared memory
Shared Pages Example
- Example of how page tables for shared code/data are organized
Structure of the Page Table
- Memory structures for paging
- Dividing page tables into smaller units
- Hierarchical paging, hashed page tables, inverted page tables
Two-Level Paging
- Dividing a 32-bit logical address into two page numbers and an offset
- Mapping to page tables
64-bit Logical Address Space
- When 64-bit logical addresses are involved
Three-Level Paging
- A variant of multilevel page table structure
- Addresses are broken down into three page numbers
Hashed Page Tables
- Hashing virtual page numbers to virtual page entries in a hash table.
Inverted Page Table
- Only one entry per physical page instead of per virtual page for a process.
Oracle SPARC Solaris
- Example of a modern 64-bit operating system
Swapping
- Moving processes between memory and a backing store.
- Total physical memory space needed for processes may exceed physical memory.
- Methods to accommodate processes
Swapping (cont.)
- Swapping issues (address binding).
- Swapping variants found in operating systems like UNIX, Linux, and Windows
Context Switch Time
- Time for switching a process to another.
- Including the swap in/out times if necessary
- Increased context switching time
Context Switch time and Swapping (cont.)
- Constraints on swapping
- Considerations for pending I/O
- Use of double buffering
Swapping on Mobile Systems
- Differences in memory management to accommodate flash-based memory, limited cycles, low throughput
Swapping with Paging
- Swapping processes that require paging.
Example: The Intel 32 and 64-bit Architectures
- Dominant processors used in modern computing.
- Typical architectures used for 32-bit and 64-bit systems
Example: The Intel IA-32 Architecture
- Supports both segmentation and segmentation with paging.
- Details about how segments are handled in the architecture
Example: The Intel IA-32 Architecture (cont.)
- CPU generating logical addresses.
Logical To Physical Address Translation
- The transformation steps from a logical address to a physical address in IA-32 architecture.
Intel IA-32 Segmentation
- The segmentation unit in a 32-bit Intel processor.
Intel IA-32 Paging Architecture
- Page directory, page table layout.
Intel IA-32 Page Address Extensions (PAE)
- Increasing address space.
Intel x86-64
- Typical architecture for the 64-bit systems.
Example: ARM Architecture
- Describes the mobile platform chip architecture.
- Methods for paging, TLBs, and memory allocations.
End of Chapter 9
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Description
This quiz covers key concepts related to main memory management in operating systems, including memory allocation, protection, and address binding. Understand how processes interact with memory and the importance of efficient memory usage. Test your knowledge on how operating systems ensure process protection and handle memory addresses.