For the valid & invalid bit, if a valid bit is on, it indicates

Question

BlackTom AI · Accepted Answer

A valid bit set (value 1) in a page table entry indicates that the corresponding virtual page currently resides in physical memory (RAM).

1. Relevant knowledge points and concepts
- Virtual memory maps virtual pages to physical frames using a page table.
- Each page table entry (PTE) typically contains a frame number and status bits; one common status bit is the valid/invalid (or present) bit.
- If the valid bit is 1, the PTE contains a valid physical frame number and the page is resident; if 0, the page is not currently present and access causes a page fault or is treated as illegal depending on OS/architecture.

2. Step-by-step reasoning process
- CPU generates a virtual address consisting of a virtual page number (VPN) and an offset.
- The MMU/indexing hardware looks up the PTE for that VPN.
- The MMU checks the PTE’s valid bit:
  - If valid = 1: use the frame number from the PTE and combine it with the offset to form the physical address; memory access proceeds.
  - If valid = 0: the MMU triggers a page fault; the OS either loads the page from disk into memory (then sets valid=1) or determines the access is illegal (segmentation fault).

3. Intermediate computation example (address translation)
- Given VPN -> PTE has frame number F and offset bits O.
- Physical address = (F << number_of_offset_bits) | offset.
- This translation is only correct when valid = 1 because F is meaningful only for resident pages.

4. Why the correct answer is correct
- The valid bit’s purpose is precisely to indicate presence: when set, the PTE holds a valid frame mapping and the page is in memory, allowing immediate translation and access.

5. Why other options are incorrect
- "the page is not in memory": this is the opposite of the valid-bit semantics; that corresponds to valid = 0.
- "the page is illegal" and "the page is not legal": an invalid bit can sometimes signal an illegal reference, but more often it signals simply “not present.” The valid bit does not universally mean “illegal”; therefore these options are inaccurate.

6. Conclusion
- The correct answer is "the page is in memory," which matches the provided answer.

For the valid & invalid bit, if a valid bit is on, it indicates单项选择题

类似问题

When the valid – invalid bit is set to valid, it means that the associated page ____________

You own a bond that pays $64 in interest annually. The face value is $1,000 and the current market price is $1,021.61. The bond matures in 11 years. What is the yield to maturity?

Which of the following statements is CORRECT?

It will cost $9,600 to acquire an ice cream cart that is expected to produce cash inflows of $3,600 a year for three years. After the three years, the cart is expected to be worthless. What is the payback period?

更多留学生实用工具

智能学习助手

风格化写作助手

论文查重助手

文献引用助手

课堂转译助手

课堂笔记助手

Quiz搜索助手

学校历年真题

智能刷题助手

智能匹配练习

希望你的学习变得更简单