Solution-

1. Number of levels of page table = 2.
2. TLB access time = 20 ns.
3. Main memory access time = 100 ns.
4. TLB Hit ratio = 80% = 0.8.

A translation lookaside buffer (TLB) is a memory cache that is used to reduce the time taken to access a user memory location. This is called a TLB hit. If the requested address is not in the TLB, it is a miss, and the translation proceeds by looking up the page table in a process called a page walk.

TLB hit ratio- A TLB hit is the no of times a virtual-to-physical address translation was already found in the TLB, instead of going all the way to the page table which is located in slower physical memory. TLB hit ratio is nothing but the ratio of TLB hits/Total no of queries into TLB.

8.10 : —- a> A paged memory reference requires 2 memory accesses: one to get the frame number for the page number from memory and actually accessing the data. So if a memory reference takes 200 nanoseconds then a paged memory reference will take 400 nanoseconds.

The ‘effective access time’ is essentially the (weighted) average time it takes to get a value from memory.

Internal Fragmentation occurs when a process needs more space than the size of allotted memory block or use less space. External Fragmentation occurs when a process is removed from the main memory. Internal Fragmentation occurs when Paging is employed. External Fragmentation occurs when Segmentation is employed.

If the probability of TLB hit is P% (TLB hit rate) then the probability of TLB miss (TLB miss rate) will be (1-P) %. Therefore, the effective access time can be defined as; EAT = P (t + m) + (1 – p) (t + k.m + m)

Because the working set of pages is quite small, a small TLB can cache nearly all page translations in practice, leading to a high hit rate and thus high efficiency.

The TLB is faster than main memory (which is where the page table resides). The typical access time is in the order of 10 ns for the TLB and 100 ns for main memory. The reasons for this are twofold: The TLB is located within the CPU, while main memory – and thus the page table – is not.

The yellow is in the middle (TLB miss, no page fault). Really the page table doesn’t point to the disk block for an invalid entry, but the effect is the same.

Cache stores the actual contents of the memory. TLB on the other hand, stores only mapping. TLB speeds up the process of locating the operands in the memory. Cache speeds up the process of reading those operands by copying them to a faster physical memory.

A CPU cache which used to store executable instructions, it’s called Instruction Cache (I-Cache). Translation Lookaside Buffer (i.e. TLB) is required only if Virtual Memory is used by a processor. In short, TLB speeds up translation of virtual address to physical address by storing page-table in a faster memory.

1 Answer. The TLB caches the translations listed in the page table. Each CPU core can be running in a different context, with different page tables. This is what you’d call the MMU, if it was a separate “unit”, so each core has its own MMU.

TLB

Acronym	Definition
TLB	Translation Lookaside Buffer
TLB	Tractor-Loader-Backhoe
TLB	Text Library
TLB	Tool Bar

When there is a TLB hit you get desired Physical address in TLB and you have to access main memory once for actual data. But if there is a TLB miss, you have to access memory twice as in above case. Many systems use more than one level of page tables, so you may need to access memory more than two times.

A translation lookaside buffer (TLB) is a memory cache that stores recent translations of virtual memory to physical addresses for faster retrieval. When a virtual memory address is referenced by a program, the search starts in the CPU. As virtual memory addresses are translated, values referenced are added to TLB.

In paging, Translation Lookaside Buffer or TLB is a solution that tries to reduce the effective access time. Paging in OS using TLB requires only one memory reference if TLB hit occurs.

In Paging, a process address space is broken into fixed sized blocks called pages. In Segmentation, a process address space is broken in varying sized blocks called sections. Operating System divides the memory into pages. During segmentation, a logical address is divided into section number and section offset.

Disadvantage of TLB scheme: if two pages use the same entry of the memory, only one of them can be remembered at once. If process is referencing both pages at same time, TLB does not work very well. Example: TLB with 64 (100 octal) slots.

• Allocating memory is easy and cheap.
• Any free page is ok, OS can take first one out of list it keeps.
• Eliminates external fragmentation.
• Data (page frames) can be scattered all over PM.
• Pages are mapped appropriately anyway.
• Allows demand paging and prepaging.
• More efficient swapping.

It can be easily used because it has a graphical user interface, and new users can run computers easily by this. Accessing hardware without writing programs: – Operating system provides us the facility to access hardware without writing programs. Through this, we can share one data with a lot of users.

Advantages. Demand paging, as opposed to loading all pages immediately: Only loads pages that are demanded by the executing process. As there is more space in main memory, more processes can be loaded, reducing the context switching time, which utilizes large amounts of resources.

Paging is a storage mechanism that allows OS to retrieve processes from the secondary storage into the main memory in the form of pages. The biggest advantage of paging is that it is easy to use memory management algorithm. Paging may cause Internal fragmentation.

In Operating Systems, Paging is a storage mechanism used to retrieve processes from the secondary storage into the main memory in the form of pages. The main memory will also be divided in the form of frames. One page of the process is to be stored in one of the frames of the memory.

Paging is used for faster access to data. When a program needs a page, it is available in the main memory as the OS copies a certain number of pages from your storage device to main memory. Paging allows the physical address space of a process to be noncontiguous.

Advantages and disadvantages of virtual memory: The size of program can be more than the size main memory. Memory can be used efficiently because a section of program loaded only when it need in CPU. Virtual memory allows sharing of code and data, unlimited amounts of multiprogramming.

Virtual Memory is better for good performance, as if you have shortage of physical memory, but on slower computer when you run heavy graphics application so It cause the hard disk problem while using more memory as virtually hard works more as RAM so a logical or physical BAD could be happen in HARD Drives, but note …

Virtual memory is a feature of an operating system that enables a computer to be able to compensate shortages of physical memory by transferring pages of data from random access memory to disk storage. This process is done temporarily and is designed to work as a combination of RAM and space on the hard disk.

SSDs are slower than RAM, but faster than HDDs. So, the obvious place for an SSD to fit into virtual memory is as swap space (swap partion in Linux; page file in Windows). I don’t know how you would do that, but I agree that it would be a bad idea, since SSDs (flash memory) are slower than RAM.

What I would say is virtual memory is not a substitute for physical RAM. Having an SSD will improve access times and responsiveness in general, but it won’t make it act like a computer with twice the amount of RAM installed.