Podcast
Questions and Answers
What is the purpose of compaction in memory management?
What is the purpose of compaction in memory management?
What is internal fragmentation in memory management?
What is internal fragmentation in memory management?
In virtual memory management, what is the purpose of a page table?
In virtual memory management, what is the purpose of a page table?
What is the standard range for page sizes in modern systems?
What is the standard range for page sizes in modern systems?
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How are pages of virtual memory mapped to physical memory frames?
How are pages of virtual memory mapped to physical memory frames?
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What is the result of adding processes into pages with demand paging?
What is the result of adding processes into pages with demand paging?
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How does compaction help reduce external fragmentation in memory management?
How does compaction help reduce external fragmentation in memory management?
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What is the role of a page table in a paging system?
What is the role of a page table in a paging system?
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Which scenario would likely lead to increased internal fragmentation?
Which scenario would likely lead to increased internal fragmentation?
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Why is it important to manage internal fragmentation in memory systems?
Why is it important to manage internal fragmentation in memory systems?
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Study Notes
Memory Management Concepts
- Physical and virtual memory are divided into equal-sized units called pages (virtual) and frames (physical).
- The address translation scheme involves breaking down the CPU-generated address into two parts:
- Page number (p): Used to index the page table containing base addresses of each physical memory page.
- Page offset (d): This works with the base address to locate the specific physical memory address.
Demand Paging
- Demand paging only loads a page into memory when accessed, improving memory efficiency.
- If a process tries to access an address with a page not currently in memory, a page fault occurs, necessitating the loading of the required page.
- If a virtual address is not allocated, the process is aborted, ensuring that pages are only loaded when demanded.
Present/Absent Pages
- Some pages may not correspond to a physical memory address and are marked as valid (1) or invalid (0) in a table.
- When an invalid page is accessed, a page fault triggers, leading to a demand for the relevant page to be loaded into memory.
Page Fault Process
- A page fault occurs when attempting to access a marked invalid page in the page table.
- The interrupt handler checks the page number:
- If the page is outside the process address space, the process is aborted.
- If the page is absent from memory, an empty frame is used to swap the page into memory.
- The status of the page is updated from invalid to valid, and the instruction causing the page fault is restarted.
Performance Impact
- Page faults affect system performance due to the additional time taken for handling the fault, referred to as page-fault service time.
Effective Access Time (EAT)
- EAT measures the average time it takes to access information, considering page faults.
- EAT formula:
- EAT = (1 - p)a + p(a + S), where:
- p = page fault rate,
- a = hardware memory access time,
- S = page fault service time.
- EAT = (1 - p)a + p(a + S), where:
- Simplified EAT: EAT = a + pS.
Factors Influencing EAT
- Increasing RAM reduces the page fault rate (p).
- Adding more processes increases the page fault rate (p).
- Enhancing disk speed leads to a decrease in service time (S).
- Page fault rates typically vary between 0 and 1.
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Description
Explore how the CPU-generated addresses are split into page numbers and offsets for address translation in memory management. Learn how page tables are used to find the base addresses of pages in physical memory, using a book analogy.
