Questions about techniques for providing the appearance of an isolated, contiguous address space to each process. The size of the address spaces may be made to appear larger than the size of main memory by moving pages or segments between main memory and a larger backing store.

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How to calculate virtual address space from page size, virtual address size and page table entry size?

I try to solve an exercise, unfortunately without any success yet. From the following given information, the virtual address space should be calculated: Page size is 16 KB Logical address size is ...
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1answer
22 views

Address space definition

I'm learning by my self about OS theory and I have some troubles to understand what is a process address space. So far, I came across two definitions of what a process address space is: 1 - The set ...
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1answer
28 views

What are logical addresses and where do they actually reside?

While studying about memory management, paging and segmentation there is a lot of usage of phrases like CPU generates logical addresses and ...
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1answer
26 views

Page vs page table entry

Im studying for OS-finals and I cant figure out the difference. A page is a chunk of addresses e.g 0-4095. This maps to 4kB of memory. This page is 4kB big. But according to the litterature the Page ...
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1answer
45 views

finding maximum virtual and physical memory

If the following is given: CPU uses a four-level hierarchical page table, each level can contain 512 entries the page size is 4KB. virtual address is 48 bits How do i get the size of the ...
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70 views

What is the primary reason more RAM makes a computer faster? [migrated]

Whilst studying for an exam I read that more RAM decreases the number of page faults. Given that handling a page fault can cost many millions of CPU cycles is this the primary reason more RAM will ...
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1answer
31 views

Virtual address lookup without using all the space to store the physical addresses [closed]

How is a virtual address mapped to a physical address? The most logical solution I, with my meager knowledge, can think of would be to actually store the physical address. The problem with the above ...
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7 views

What is the on-demand mapping in the kernel virtual memory in Linux? [migrated]

In the OS lecture, the lecturer explained that not all the physical memory will fit into virtual address space on a 32-bit architecture. So what the kernel can do is map anything else above 896MB ...
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46 views

Number of addresses in a memory region

So I am looking at some Operating Systems exercises and we have A swapping system eliminates holes by compaction. Assuming a random distribution of many holes and many data segments ...
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47 views

What's the difference between clock replacement & LRU replacement?

As title. When we want to request following page numbers 2,4,4,2,5,2,1,1,3,1, is clock replacement better? What are the advantages and disadvantages of them? Thanks~
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1answer
47 views

Why is the processes address space a continuous block in RAM?

I need some clarification regarding how the process address space is organized in memory. I went through basic concepts of virtual memory and adress translation and according to the size of the page, ...
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1answer
208 views

Virtual Address and Physical Address Space

A machine has 48-bit virtual addresses and 32-bit physical addresses. Pages are 8K. How many entries are needed for a conventional page table ? The answer is 2^35 entries Why not (2^32) / (2^13) = ...
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2answers
75 views

Difference between virtual memory and job pool

Both virtual memory and job pools store the processes temporarily on disk and bring them to memory at some later stage, so what is the actual difference in between them? What I guess is that when a ...
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1answer
71 views

Why is data fragmentation not possible on main memory (RAM)?

I am wondering why data fragmentation is a problem on main memory. On a software level, virtual addresses are used anyway. So why can one address space not be split up into multiple segments, like a ...
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2answers
298 views

How to calculate the size of a page in a two level paging CPU?

I am having difficulties with understanding the concept of paging. As a result I've got no idea how I can solve the following exercise - I'm lacking one more equation to solve it. I've read a lot ...
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1answer
77 views

Page management in OS kernels

I looked at some old OS theory books of mine and noticed that one glaring omission in all of these OS books is how to actually keep track of physical pages that are free (i.e. algorithms for actually ...
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1answer
43 views

In an Inverted Page Table, will following chains happen very often for small addresses?

I just learned about the Inverted Page Table and immediately thought about the chaining model used. If two processes use the same virtual address, resolving the address will have to include following ...
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1answer
81 views

Understanding Logical to Physical Addressing

I am trying to understand the concept of logical to physical addressing. I am given 72 physical addresses (0-71) with values A virtual address = 2^(p+w) p = page bits w = word bits I know the page ...
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2answers
1k views

Would it be possible to use the cloud for RAM?

I'm not sure if this is the right place to ask but I had this idea. Since the cloud can be used for storing memory, would it be possible to use it for RAM too?
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0answers
48 views

When there's no memory, should malloc or read/write fail?

To my surprise, I recently found out that Windows would fail a large memory allocation even if little of said memory is to actually be used, e.g. even if you don't want the swap, you better not ...
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1answer
344 views

Page Table Size in a 4 Level Hierarchical Page Table

An Intel 64 bit CPU uses a four-level hierarchical page table. Each of the four levels of the page table can contain 512 entries, and the page table size is 4KB. You should be able to see that it ...
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1answer
216 views
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122 views

How does cpu fetch active program data (using virtual address) from storage when there is a page fault?

I read that cpu generates virtual address and using the same mmu translates to physical address and then fetches the data from RAM. But when there is a page fault, the data is fetched from the HDD(or ...
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2answers
182 views

Why does quicksort work well with virtual memory?

Introduction to Algorithms said that quicksort "works well even in virtual-memory environments," but didn't explain why. I've tried looking an Wikipedia and Stack Exchange, but found no reason why. Is ...
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1answer
19 views

Why we need tagbits when we already have indexbit and offset?

I was watching a lecture and got confused at one point when professor said that to distinguish between two addresses having same values of offset as well as index bit we need tag.Why we need tag ? for ...
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1answer
188 views

What is the overhead of Virtual Memory?

What is the price paid for the vast virtual address space provided to programmers for their applications? Or in other words, what is the overhead due to virtual memory? Is there any other overhead ...
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1answer
667 views

Does Second chance Page replacement algorithm suffer with Belady's anomaly?

In Second chance Page replacement algorithm(clock algorithm), if all the Reference bits are set to one, then the algorithm behaves just as FIFO. Considering this case, can we conclude that Second ...
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1answer
679 views

What problem does cache coloring solve?

According to what I have read from two different sources, cache coloring is (was?) required in order to: Counter the problem of aliasing: Prevent two different virtual addresses with the same ...
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2answers
254 views

Operating System Paging concept

I am quoting a paragraph from the book "Operating System Principles" by Galvin. Usually, each page-table entry is 4 bytes long, but that size can vary as well. A 32-bit entry can point to one of ...
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1answer
49 views

Role of the MMU in a Page Fault Swap

When a virtual memory address outside the range of loaded into physical RAM is referenced and a page fault occurs, does the Memory Management Unit rely on DMA (Direct Memory Access) to swap the ...
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65 views

Roles of the Memory Management Unit

I know that the first instruction stored in BIOS is "mapped" to memory address 0, and that a signal on the reset pin to the microprocessor causes this instruction to be fetched, beginning the POST and ...
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1answer
283 views

How are system calls handled in a virtual machine?

Quoting wikipedia, a system call is: In computing, a system call is how a program requests a service from an operating system's kernel. This may include hardware related services (e.g. ...
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1answer
112 views

Memory ballooning in the OS

Some hypervisors optimize memory usage using a method that is called ballooning (at least that's what KVM calls it), this method deduplicates memory between VMs and sets common pages to read-only with ...
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1answer
40 views

Name for almost random memory distribution on the heap

If I had a heap like the following: with blue blocks being occupied memory and white blocks being free memory What is the general name given to the situation illustrated, where the free and ...
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0answers
117 views

What are current cache algorithms and cache strategies?

Which cache strategies/algorithms (especially for L2 Cache) are used in practice and don't exist solely in research/theory? There is a list on Wikipedia which does not state which algorithms are ...
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1answer
45 views

In Pagination, how does the S.O. knows where the page is in secondary Memory?

So every process has its own Page Table, the page table references the frame where the page is in physical memory and also has a valid-invalid bit that tells whether it is in physical memory or in ...
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1answer
171 views

Maximum amount of memory that can be allocated to a process

DISCLAIMER: The following scenario was taken from an assignment I got in a OS course I'm taking, and it arose a lot of question marks in my head. However non of the questions asked by myself here ...
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2answers
10k views

Clock page replacement algorithm - Already existing pages

When simulating the clock page replacement algorithm, when a reference comes in which is already in memory, does the clock hand still increment? Here is an example: With 4 slots, using the clock ...
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1answer
399 views

Does virtual address space resides in virtual memory?

I have several confusion like : Does virtual address space resides in virtual memory ? Does each process has its own virtual address space like each process has its own virtual memory and own page ...
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1answer
105 views
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1answer
5k views

How does a TLB and data cache work?

I'm trying to study for an exam and I realized I'm confused about how the TLB and data cache work. I understand that the TLB is essentially a cache of most recently used physical addresses. However, ...
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1answer
1k views

Understanding the basic concepts in memory organisation

(Before actually proceeding to the question, I want to confess that this is a homework question, please do consider it and help me in improving my understanding a bit more.) I have recently started ...
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1answer
334 views

Segmentation and paging

I am given a system with a segmented paging architecture. Both physical and virtual address spaces contain $2^{16}$ bytes each. The virtual address space is divided in $8$ equal size segments. The ...
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1answer
195 views

How a program is copied to RAM from harddisk

I know that for executing a program, it should be copied to RAM. But the problem is whole of it may not be copied always. Since the size of the RAM is limited, there is mechanism called virtual ...
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2answers
4k views

Given the logical address, how to extract the page number?

I am studying Computer Systems. I have th following question and its answer: Given the logical address 0xAEF9 (in hexadecimal) with a page size of 256 bytes, what is the page number? ...
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1answer
2k views

Look Ahead buffer vs Translation Look aside buffer

I know that Translation look aside buffer is used for address translation in paging to achieve better performance. I came across term called Look Ahead buffer in a document which said it implements ...
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1answer
260 views

clarification about Algorithm of page replacement LRU with reference bits

Studying LRU approximation Algorithms I think to have not understand how it works, for example: ...
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2answers
6k views

Calculation of effective average instruction execution time in a 2-level paging system

System has a two level paging scheme Average CPU time for a instruction = 100ns Average number of memory accesses per instruction = 2 Regular memory access = 150 ns Page fault service ...
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2answers
7k views

How does increasing the page size affect the number of page faults?

If we let the physical memory size remain constant, What effect does the size of the page have on the number of frames? What effect does the number of frames have on the number of page faults? ...
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1answer
3k views

Program compilation and execution flow

I was studying operating system concepts from Silberschatz, Galvin and Gagne's book (sixth edition) and I have some questions about the flow of execution of a program. A figure explains the processing ...