Computer Memory Management Quiz
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Questions and Answers

What must happen for a program to be executed?

  • It requires conversion into binary form.
  • It needs to be stored on a hard drive.
  • It must be communicated through the network.
  • It has to be brought into memory and placed within a process. (correct)

    • Which component sits between main memory and CPU registers to improve access time?

  • Secondary storage
  • Cache (correct)
  • RAM
  • Hard disk drive

    • What is the role of protection in memory management?

  • To enhance processing speeds for all applications.
  • To ensure a process can only access specific addresses. (correct)
  • To allocate memory based on real-time usage.
  • To limit the total memory usage of the operating system.

    • Why does main memory often cause stalls during processing?

    <p>It requires multiple clock cycles for access. (D)</p> Signup and view all the answers

    What does a memory unit primarily process?

    <p>A stream of addresses and access requests. (B)</p> Signup and view all the answers

    What kind of architectures does the Intel Pentium support?

    <p>Segmentation with paging and pure segmentation. (C)</p> Signup and view all the answers

    In what way does continuous memory allocation differ from paging?

    <p>Paging allows for fragmented memory utilization. (D)</p> Signup and view all the answers

    What resource does the CPU use to access memory?

    <p>Address and read/write requests. (B)</p> Signup and view all the answers

    What is the internal fragmentation when the page size is 2,048 bytes and the process size is 72,766 bytes?

    <p>962 bytes (C)</p> Signup and view all the answers

    How many frames does the physical memory accommodate if the total size is 32 bytes and each page size is 4 bytes?

    <p>8 frames (B)</p> Signup and view all the answers

    What does the Page-table base register (PTBR) do in a paging system?

    <p>Points to the page table in main memory (C)</p> Signup and view all the answers

    Which of the following best describes the average fragmentation in a paging system?

    <p>Half of the frame size (D)</p> Signup and view all the answers

    What is the purpose of translation lookaside buffers (TLBs) in a paging system?

    <p>To speed up data/instruction access (C)</p> Signup and view all the answers

    What is the primary purpose of swapping a process out of memory?

    <p>To temporarily free up memory for higher-priority processes (B)</p> Signup and view all the answers

    Which of the following describes the backing store used in swapping?

    <p>A fast disk large enough to accommodate all memory images (A)</p> Signup and view all the answers

    What does the term 'roll out, roll in' refer to in the context of swapping?

    <p>A swapping variant used for priority-based scheduling (C)</p> Signup and view all the answers

    What factor primarily contributes to the total transfer time during swapping?

    <p>The amount of memory being swapped (A)</p> Signup and view all the answers

    Is it necessary for a swapped out process to return to the same physical addresses when swapped back in?

    <p>No, it can return to any available physical addresses (A)</p> Signup and view all the answers

    Which memory allocation strategy searches the entire list to allocate the smallest hole that is big enough?

    <p>Best-fit (A)</p> Signup and view all the answers

    What type of fragmentation occurs when allocated memory is slightly larger than requested memory?

    <p>Internal Fragmentation (D)</p> Signup and view all the answers

    What method can be used to reduce external fragmentation in memory management?

    <p>Compaction (B)</p> Signup and view all the answers

    How does the first-fit allocation method affect memory fragmentation?

    <p>Half of the allocated blocks may be lost to fragmentation. (D)</p> Signup and view all the answers

    What is the physical address space division based on in paging?

    <p>Fixed-sized pages (A)</p> Signup and view all the answers

    What is the main goal of the architecture described for modern operating systems?

    <p>Efficiency and low overhead (D)</p> Signup and view all the answers

    In address translation, which component is used to define the physical memory address that is sent to the memory unit?

    <p>Page offset (B)</p> Signup and view all the answers

    In the inverted page table architecture, what are the two types of hash tables used?

    <p>One kernel and one for all user processes (C)</p> Signup and view all the answers

    What does each entry in the hash tables represent?

    <p>A contiguous area of mapped virtual memory (C)</p> Signup and view all the answers

    What is a key disadvantage of the worst-fit allocation strategy?

    <p>It requires a search of the entire list. (D)</p> Signup and view all the answers

    What functionality does the Translation Lookaside Buffer (TLB) provide?

    <p>Fast hardware lookups of translation entries (B)</p> Signup and view all the answers

    What is the term for memory space that is available but not contiguous?

    <p>External Fragmentation (A)</p> Signup and view all the answers

    What happens when a virtual address reference misses in the TLB?

    <p>It causes an interrupt to update the cache (A)</p> Signup and view all the answers

    Which factor primarily influences the effectiveness of paging in avoiding fragmentation?

    <p>Fixed-sized frames (A)</p> Signup and view all the answers

    Which memory allocation strategy is generally faster and more efficient in terms of storage utilization?

    <p>First-fit and best-fit (D)</p> Signup and view all the answers

    How does the kernel respond when it does not find a match in the TLB or TSB?

    <p>It initiates a search in the hash table (A)</p> Signup and view all the answers

    What is stored in the Translation Storage Buffer (TSB)?

    <p>Entries for recently accessed pages (B)</p> Signup and view all the answers

    What is included in each entry of the hash table?

    <p>The base address and span of the memory region (B)</p> Signup and view all the answers

    What role does the relocation register play in memory management?

    <p>It adds a value to addresses generated by a user process. (D)</p> Signup and view all the answers

    Which statement accurately describes dynamic loading?

    <p>Routines are loaded only when they are called. (D)</p> Signup and view all the answers

    In dynamic linking, what is the purpose of the stub?

    <p>To locate the appropriate memory-resident library routine. (A)</p> Signup and view all the answers

    How does contiguous allocation of memory typically arrange partitions?

    <p>User processes are held in high memory while the operating system is in low memory. (C)</p> Signup and view all the answers

    What is the function of the limit register in memory management?

    <p>It defines the range of logical addresses allowed. (C)</p> Signup and view all the answers

    What does variable partitioning offer compared to fixed partitioning?

    <p>It allows flexibility in the size of partitions based on process needs. (D)</p> Signup and view all the answers

    What is a 'hole' in the context of variable partition allocation?

    <p>A segment of memory that can be allocated to processes. (C)</p> Signup and view all the answers

    What is the main challenge addressed by dynamic storage allocation?

    <p>Satisfying memory requests from a list of available free spaces. (D)</p> Signup and view all the answers

    Why are shared libraries advantageous in a dynamic linking system?

    <p>They reduce memory usage and improve efficiency by allowing multiple processes to share a common library. (C)</p> Signup and view all the answers

    What is a limitation of the multiple-partition allocation method?

    <p>It restricts the degree of multiprogramming based on the number of partitions. (A)</p> Signup and view all the answers

    Flashcards

    Process Address Space

    A region of memory that a process can access directly. This includes both main memory and registers. The CPU can only access these locations directly.

    Memory Protection

    A technique where the operating system prevents processes from accessing memory locations that are not allocated to them. This helps protect the integrity of the system and other running programs.

    Program Loading

    The process of loading a program from secondary storage (disk) into main memory so that it can be executed by the CPU. This is typically done using a technique called swapping.

    Cache

    A component of the computer system that is much faster than main memory and acts as a temporary store for frequently used data. This improves the overall performance of the system by reducing the number of accesses to main memory.

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    Memory Management

    A mechanism for managing the allocation of memory to different processes. It allows the operating system to divide the available memory into smaller pieces and assign them to various processes.

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    Relocation Register

    A register that stores a base address to be added to logical addresses generated by a process, enabling it to access physical memory locations.

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    Dynamic Loading

    The process of loading a program into memory only when it is needed, rather than at the start of execution. This improves memory utilization and efficiency.

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    Stub (Dynamic Linking)

    A small stub of code used to locate the appropriate memory-resident library routine during execution. It replaces itself with the address of the routine and executes it.

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    Dynamic Linking

    Linking the program code and system libraries during execution time, rather than before. This allows for flexibility and reduces the size of the executable file.

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    Variable Partition Allocation

    A technique that divides memory into multiple partitions, each of which can hold a single process. This allows multiple processes to run concurrently, but requires careful management of memory allocation and deallocation.

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    Hole (Memory Allocation)

    A block of memory that is not allocated to any process. These holes can be of various sizes and are scattered throughout memory.

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    Dynamic Storage Allocation Problem

    The process of finding a hole in memory large enough to accommodate a newly arriving process. This involves searching for the best fit among available holes.

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    Limit Register

    A register that contains the value of the upper limit of the logical address range that a process can access. It prevents a process from accessing memory locations that are not allocated to it.

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    Memory Management Unit (MMU)

    A special hardware unit that maps logical addresses generated by a process to their corresponding physical addresses in memory. This process includes applying relocation and limits to ensure safe access to memory.

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    Contiguous Allocation

    Contiguous allocation is a memory management technique where each process is allocated a single contiguous block of memory. This means that processes cannot be fragmented and must be loaded into a large enough space.

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    Internal Fragmentation

    The amount of memory that is wasted due to the allocation of memory in fixed-size units (pages). This occurs when a process's memory requirement is not an exact multiple of the page size.

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    Translation Look-aside Buffer (TLB)

    A special type of cache that is used to store recently accessed page table entries (PTEs) to improve performance and reduce the need for repeated memory accesses. It acts as a fast lookup table for page translation.

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    Page Size

    The size of a page in a virtual memory system.

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    Page Table

    A table that keeps track of the location of pages in main memory. Each entry in the table corresponds to a page in the virtual memory space.

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    Paging

    The process of dividing a process's memory space into fixed-size units called pages. These pages can be loaded into main memory independently.

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    First-Fit Memory Allocation

    A memory allocation strategy where the first available space in memory that is large enough is allocated to the process.

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    Best-Fit Memory Allocation

    A memory allocation strategy where the smallest available space in memory that is large enough is allocated to the process. This requires searching the entire memory space.

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    Worst-Fit Memory Allocation

    A memory allocation strategy where the largest available space in memory is allocated to the process. This also requires searching the entire memory space.

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    Memory Compaction

    A process of rearranging memory contents to combine all free memory into one large block, reducing external fragmentation.

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    Address Translation

    The process of dividing a logical address into two parts: a page number and a page offset. The page number is used as an index into the page table, while the page offset is used as the offset into the physical frame.

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    Inverted Page Table

    A memory management technique that uses a single hash table to map virtual addresses to physical addresses for all processes.

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    Span

    A contiguous block of virtual memory that is mapped to contiguous physical memory.

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    Tightly Integrated Hardware

    A modern operating system architecture that emphasizes efficiency and low overhead.

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    Translation Storage Buffer (TSB)

    A hardware component that stores translation table entries (TTEs) for faster lookups in the TLB.

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    TLB/TSB Search

    The process of locating a specific translation table entry (TTE) within the TLB or TSB.

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    Kernel Interrupt

    The action taken by the operating system when a TLB miss occurs, involving searching the hash table and updating the TSB.

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    Swapping

    A technique where a process is temporarily moved from main memory to a backing store (like a hard drive) to free up space for other processes. The process is then brought back into memory when needed for execution.

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    Backing store

    A large disk that stores copies of all memory images for all users. It allows processes to be swapped in and out of memory efficiently.

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    Roll out, roll in

    A variant of swapping used in priority-based scheduling. A lower-priority process is swapped out to make space for a higher-priority process. This allows the higher-priority process to be executed immediately.

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    Swap time

    The time it takes to transfer a process's memory image between main memory and the backing store. It is a major factor in the overall performance of swapping.

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    Ready queue

    A queue that contains processes that are ready to be executed but are currently waiting for their memory images to be loaded into main memory.

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    Study Notes

    Memory Management

    • Memory management is a crucial operating system function, handling how programs and data are stored and accessed.
    • Programs initially reside on disk. They must be loaded into main memory to run.
    • Main memory and registers are the only storage locations directly accessible by the CPU.
    • The memory unit only sees addresses and data read/write operations. Register operations are much faster than memory operations.
    • Protection is needed, ensuring a process accesses only its assigned memory addresses. This is handled using base and limit registers.
    • Hardware checks if the address generated by the CPU is between the base and limit values for the user.
    • Instructions for loading base and limit registers are typically privileged.
    • Programs are represented differently during development versus execution. Binding of instructions occurs at compile time, load time, or execution time.
    • Dynamic loading is an approach where routines are loaded on demand, optimizing memory use; unused routines are never loaded.
    • Dynamic linking postpones linking until execution time. A stub locates the relevant library routine.
    • Contiguous allocation divides main memory into partitions. Resident OS is in lower memory. Processes have a single, contiguous partition higher in memory.
    • Relocation registers protect user processes and OS code from each other and from changes. Limit registers define the valid range of logical addresses.
    • Various algorithms (first-fit, best-fit, worst-fit) exist for dynamically allocating memory from a list of free holes.
    • External fragmentation occurs when available memory is scattered in small, non-contiguous segments, limiting its use. Analogy is like scattered fragments of paper on a desk rather than an entire piece.
    • Internal fragmentation occurs when allocated memory is larger than requested. This is the difference between allocated block size and requested block size.
    • Compaction is a method for reducing external fragmentation by shifting memory segments to create contiguous free space.
    • Paging divides both physical and logical memory into fixed-sized blocks or frames and pages. It avoids external and varying size memory chunk problems.
    • Pages and frames are the same size.
    • A page table maps logical addresses to physical addresses.
    • The CPU generates a page number and a page offset.
    • The page number is used as an index into a page table.
    • The page offset is combined with the frame base address to form the physical address.
    • Paging hardware translates logical address to physical address using page table and page number.
    • A TLB (Translation Lookaside Buffer) is a special cache that stores recent translations, speeding up address lookups.
    • If a page is not in the TLB (TLB Miss), it must be retrieved from the page table, this may be slow. Overall time is more efficient if values are found in the TLB (TLB Hit)
    • Memory protection is handled by valid-invalid bits in the page table; marking a page as "valid" ensures it resides within the process's logical address space. Marking as "invalid" means it doesn't.
    • Shared pages allow multiple processes to share read-only code (e.g., text editors), improving memory utilization and facilitating interprocess communication.
    • Private pages are for each process's exclusive code/data segments.
    • Different Memory organizations for Paging include hierarchical page tables, hashed page tables, and inverted page tables
    • Hierarchical paging divides the page table into smaller, more manageable parts.
    • Hashed page tables use a hash function to map virtual addresses to page table entries.
    • Inverted page tables maintain a single table to track all physical pages, rather than individual tables per process.
    • Swapping is a technique for moving processes between main memory and backing store (typically a fast disk).
    • If the next process is not in main memory, a process must be swapped out to make room for the new process.
    • Swapping between CPU and disk is slow.
    • Swapping is less common in modern operating systems.

    Memory Management on Mobile Systems

    • On mobile systems, swapping is typically not supported due to flash memory's characteristics.
    • Swapping is not needed either as memory may not be fully utilized as on desktop systems. Apps voluntarily free memory in these systems.

    Example Architectures

    • Intel IA-32 CPUs support both segmentation and paging.
    • IA-32 organization divides available space into 8Kb to 4Gb sections.
    • The Intel x86-64 architecture supports 64-bit virtual addressing and physical addressing. It enables access greater than 4GB of memory.
    • The ARM architecture used in mobile devices typically employs one-level paging for sections.

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    Chapter 9: Main Memory PDF

    Description

    Test your knowledge on the fundamentals of computer memory management. This quiz covers topics such as memory execution, paging, fragmentation, and the functions of key memory components like TLBs and PTBR. Perfect for students studying computer architecture and operating systems.

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