Questions tagged [paging]
Questions about memory-management techniques where the computer manages and transfers data between main memory and secondary storage in pages -- discrete chunks of a fixed size. Operating systems often use paging to implement virtual memory.
92
questions
0
votes
0
answers
11
views
An excercise on Pagin and Page tables
I have an exercise on paging and page tables that I can't get my head around.
So the data is: my virtual addresses are 32 bits long, 1 page is 1 KiB, 1 PTE is 32 bits big and 1 page table is 1 page.
...
0
votes
0
answers
26
views
How to calculate page number of pages and page size for multilevel paging?
I have the following virtual address:
+---------+----------+----------+
+ 7 Bit x | 13 Bit y | Offset d +
+---------+----------+----------+
I now have the ...
2
votes
1
answer
56
views
How does caching, paging, virtual memory, and OS all tie together for UNIX copy-on-write?
In my OS course, the instructor mentioned the following: In UNIX if a parent process creates a new child ("fork") then the child is an exact duplicate of the parent. This means its memory ...
- 123
0
votes
1
answer
57
views
What is the relationship between virtual address and physical address?
I am recently studying the operating system, and I found the paging system a little bit confusing, for example, what will happen when there is a 52-bit virtual address and a 40-bit physical address, ...
- 17
0
votes
2
answers
83
views
How many bits are needed to reference physical vs virtual addresses?
I trying to learn about virtual memory at the moment and one of the explanations I've look at has a diagram like below. You can see that 32 bit virtual addresses are used so the virtual address space ...
- 1
0
votes
2
answers
563
views
Calculate Physical Address Corresponding to Logical Addresses
Consider a logical address space of 4096, page size = 1024
physical memory = 8192
$\begin{array} {|c|c|}
\hline
\text{Page No} & \text{Frame No} \\
\hline
0 &7 \\
\hline
1 &4 \\
\hline
2 &...
0
votes
0
answers
33
views
Question Regarding number of frames required for multilevel page tables
I have a problem and I'm not sure where I am going wrong with this, description
so as you can see it is given a 3 level paging system with 8 bit page index on every level, now I break down logical ...
- 219
2
votes
0
answers
55
views
Exceeding limits of virtual address space
I still am confused whether I am asking the right question but here goes
Consider a X bit processor. It can address theoretically a main memory of 2^x bytes(assuming byte addressable). Now consider an ...
- 980
0
votes
1
answer
47
views
Can Operating system allocate a page of process to any free frame in memory?
Consider I have a user program of 6 pages and 4 byte page size. Now my memory has 300 frames out of which 10 frames are free for allocation. Can the OS allocate page 1 of the given process to any of ...
- 1
1
vote
2
answers
438
views
How could a page be invalid in demand paging?
I was reflecting on what I learned about demand paging and I have a question:
In demand paging, we have entries in the page table only for frames that are present in physical memory. So I was ...
- 211
2
votes
3
answers
3k
views
Why does page size affect page table size?
I am revising operating systems theory (I'm Italian, forgive me for bad English) and there is a slide that states:
If page size is small then we avoid internal fragmentation (I get that) but
we have ...
- 211
0
votes
2
answers
955
views
Understanding how internal fragmentation occurs in systems using only paging with huge page size
The excerpt below is from the OS text by Galvin et. al.
When we use a paging scheme, we have no external fragmentation: any free frame can be allocated to a process that needs it. However, we may ...
- 1,052
0
votes
1
answer
148
views
Are Paging and page cache the same in Operating system?
I was looking at paging in OS.
It seems like there are two concepts with the same name but with different features, and I wanted to be clear about those, Paging and page cache.
Before I thought paging ...
- 3
0
votes
1
answer
100
views
Are pages moved to the disk when the process is scheduled?
When process A has run long enough and the scheduler decides to run process B, will all the pages of process A be moved to the disk or they remain in the main memory?
- 139
0
votes
1
answer
359
views
Where are process pages stored - in the swap space or under file system? Can demand paging work without space space?
The Galvin OS text says that on older systems, there used to be a method, where the entire running process (when in idle state) was moved from the main memory (when main memory ran low) to the disk ...
- 1,052
1
vote
0
answers
45
views
How could one construct a TLB so that not all the bits of the presented address need match to result in a hit?
I was wondering besides the typical matching of all bits in the presented address to the resulting page, is there another way of doing so? what are the benefits/ cons and how would one go about doing ...
1
vote
1
answer
1k
views
How page table base register (PTBR) is used to locate the correct frame using Page Number?
I was reading about paging in OS , and one of the things I saw was the page table base register (PTBR).
If the CPU generates a logical address (Consists of Page number + Offset) it needs to be mapped ...
- 111
4
votes
1
answer
1k
views
Why do we need hashed page tables for Paging in Operating Systems?
I understand that we might need hierarchical paging to handle page tables with sizes greater than the size of one frame, but what is the use of Hashed Page tables then? I would understand if we were ...
- 43
2
votes
1
answer
88
views
Paging only for user code. What about kernel code?
Why is paging done only for user code (user space)? I know that the basic intuition behind paging is for managing larger logical address space in smaller physical main memory space. Won't the kernel ...
0
votes
1
answer
761
views
When is it best to use the second chance replacement algorithm?
I'm going through 'Operating Concepts' by Silberschatz, Galvin and Gagne (The Dinosaur Book) and it mentions the Second-Chance Algorithm (not enhanced) as an improvement on the FIFO replacement ...
1
vote
1
answer
426
views
Is physical pages zeroed out before it's mapped to a virtual page?
I don't how this works. According to me if the physical memory is not cleared then there is some security risk as there may be some sensitive information in it from the other processes. How does the ...
- 13
5
votes
1
answer
703
views
How does a TLB lookup compare all keys simultaneously?
I am reading OS Concepts dinosaur book which says, "Each entry in the TLB consists of two parts: a key (or tag) and a value. When the associative memory is presented with an item, the item is compared ...
- 207
1
vote
1
answer
360
views
Paging - access less than a page of memory
I'm having a bit of trouble understanding how less than a page of memory can be used.
From what I understand, memory is given out in page size chunks - say pages are 4096 bytes, and 4 bytes are ...
- 113
0
votes
0
answers
85
views
How many page-table entries are needed in case the program uses the whole logical address space
Say I have:
page size = 2^12 bytes
physical memory = 2^24 bytes
logical address space = 2^32
How many page-table entries are needed in case the program uses the whole logical address space?
- 101
-2
votes
1
answer
697
views
Converting physical address to logical
In 8-bit address space there are 16 pages and the page table stores:
68792EA51BD3CF04 (hex)
The physical address is 39h, what is the corresponding logical address?
I have literally no idea what to ...
- 1
1
vote
1
answer
89
views
How are logical addresses of instruction operands mapped to physical addresses?
Is address translation for all operands in single instruction done only once and then are all operands fetched continuously?
For example, consider any dummy instruction ...
- 1,607
0
votes
2
answers
2k
views
Why does paging not have external fragmentation?
I have read that paging does not suffer from external fragmentation as the frames and the pages are all of the equal sizes, but when we store a last level page table in a frame at that time it may not ...
user106464
0
votes
1
answer
844
views
Understanding paging and internal fragmentation
I am currently studing questions but stuck on this one, I hope someone can help me out to understand.
Question: Assume that we have a paged virtual memory with a page size of 4Ki byte. Assume that ...
- 115
2
votes
2
answers
2k
views
Difference between present - absent bit and valid - invalid bit in a page table?
while reading I found this:
Present/Absent bit – Present or absent bit says whether a particular page you are looking for is present or absent. In case if it is not present, that is called Page ...
- 53
2
votes
1
answer
749
views
What does it mean " The outer level page table need not be page aligned?
The question is in context to multilevel page table. I was trying to solve numerical on multi-level paging and noticed that page size might not be same at all levels. I came across the point "Outer ...
0
votes
1
answer
641
views
Multi-level Paging
Consider a system which has 2 level paging.The page table is divided into 2K pages and each page is having 4K entries.Memory is word addressable and Physical address space is 64MW which is divided ...
- 329
4
votes
1
answer
1k
views
How does hashed inverted page table work?
I understand hash function and inverted page table, but then the book I read describes something called hashed inverted page table (use hash to accelerate the finding because IPT is large), with TLB ...
- 314
1
vote
0
answers
524
views
pool of free page frames OS
I read that in a paging scheme memory management, some os's have a paging daemon that wakes up periodically to inspect the memory of the RAM. This is to ensure that modified pages can be scheduled to ...
- 131
0
votes
1
answer
239
views
Page Replacement optimal verses MRU
A computer has twenty physical page frames which contain pages numbered 101 through 120. Now a program accesses the pages numbered 1, 2, …, 100 in that order, and repeats the access sequence THRICE. ...
- 219
1
vote
1
answer
5k
views
How to find the virtual pages and physical memory frames?
So i am given a system of 20 bits virtual addresses and 18 bits physical addresses using paging with pages size 4Kbytes.
I am told to find the maximum number of virtual pages that a process can have ...
- 13
0
votes
1
answer
37
views
Linux OS/HW VM cooperation
From what i've learned, the HW is responsible for setting the accessed and dirty bits in the PTE of a process, and the OS is responsible for turning them off.
My question is why?
The first part, i ...
- 125
0
votes
1
answer
3k
views
What does "higher order address bits" and "lower order address bits" mean?
"Assume a system with 4 GB virtual memory and 1 GB physical memory with 32 bit addresses. if the page size is 4 KB, How many bits will be allocated as the Higher Order Address bits and Lower Order ...
1
vote
2
answers
343
views
Does the Working Set Paging Algorithm use a separate page table?
I am doing research on paging algorithms. While learning about the working set algorithm from several scientific sources I was not really able to figure out where exactly the working set is defined or ...
1
vote
2
answers
702
views
What is the difference between a page and thread?
"Each process that is executed is divided into blocks of same size, called pages."
"Thread is a part of process being executed."
Are pages and threads both part(s) of process? Whats the difference ...
0
votes
1
answer
1k
views
What happens when all reference bits set to 1 in Second Chance Page Replacement Algorithm?
I have a sequence like 5577334... and there are 3 frames available.
After the 6th clock, all pages (5, 7 and 3) will have their reference bits set to 1.
Now, when 4 comes in, 5 will go even though ...
- 11
1
vote
1
answer
14k
views
Explain Hashed page tables in operating system
I have a difficult time understanding hashed page tables used in virtual memory management. Here is picture of the slide that I am referring to:
I understand that p is hashed and then the hash is ...
- 13
1
vote
1
answer
701
views
Difference between inverted page table and a standard one?
I know that for standard page tables each process would have its own page table and for inverted the OS would have it.
But other than this what are the main differences between a standard page table ...
0
votes
1
answer
642
views
Effectiveness of TLB
This is a book question:
Suppose that a machine has 48-bit virtual addresses and 32-bit
physical addresses.
Suppose this same system has a TLB (Translation Lookaside Buffer) with
32 ...
- 101
0
votes
1
answer
4k
views
Operating System: Performance of Demand Paging
I am reading Operating systems from the book "Operating System Concepts" by Peter Baer Galvin, 7th edition.
Performance of Demand Paging:
Let p be the probability of a page fault (0 $\leqslant$...
- 215
1
vote
2
answers
184
views
If you increase the address space for an OS, does the Phys Mem used by the program increase?
I am learning about the OS.
I know: that Address Space Size = # of pages x page size
So if I increase Address Space Size, then the number of pages increases:(not the page size). However, isn't the ...
0
votes
2
answers
2k
views
Why page size = size of one cache way?
Why is that the page size equals the size of one cache way?
My book states "A direct-mapped cache cannot be bigger than a page".
- 105
3
votes
5
answers
22k
views
Why do we need the valid-invalid bit in a page table?
I'm reading about memory management in Operating System Concepts, by A. Silberschatz. The author says:
[...] the user process by definition is unable to access memory it does not own.
It has no ...
user76258
1
vote
1
answer
53
views
Is the term page replacement actually a misnomer?
My understanding is that "page replacement" entails replacing the contents of a frame to bring in a new frame in it's place corresponding to a new page. Since it is not the page, but the frame that ...
- 13
1
vote
1
answer
5k
views
What is the difference between caching, buffering and paging? Expecting a detailed answer on the OS level
I have been reading about caching and buffering it seems about the same to me can't get hold of the differences clearly and paging, for now the only difference I understand between paging and caching ...
- 111
2
votes
1
answer
1k
views
Operating system maintains copy of page table for each process
I am quoting a paragraph in Operating System Concepts by Silberschatz, in paging chapter,
In addition, the operating system must be aware that user processes operate
in user space, and all ...
