What is swap space in windows

A computer has sufficient amount of physical memory but most of times we need more so we swap some memory on disk. Swap space is a space on hard disk which is a substitute of physical memory. It is used as virtual memory which contains process memory image. Whenever our computer run short of physical memory it uses it’s virtual memory and stores information in memory on disk. Swap space helps the computer’s operating system in pretending that it have more RAM than it actually has. It is also called as swap file.This interchange of data between virtual memory and real memory is called as swapping and space on disk as “swap space”.

Virtual memory is a combination of RAM and disk space that running processes can use. Swap space is the portion of virtual memory that is on the hard disk, used when RAM is full.

Swap space can be useful to computer in various ways:

• It can be used as a single contiguous memory which reduces i/o operations to read or write a file.
• Applications which are not used or are used less can be kept in swap file.
• Having sufficient swap file helps the system keep some physical memory free all the time.
• The space in physical memory which has been freed due to swap space can be used by OS for some other important tasks.

In operating systems such as Windows, Linux, etc systems provide a certain amount of swap space by default which can be changed by users according to their needs. If you don’t want to use virtual memory you can easily disable it all together but in case if you run out of memory then kernel will kill some of the processes in order to create a sufficient amount of space in physical memory. So it totally depends upon user whether he wants to use swap space or not.

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swap file (swap space or pagefile)

A swap file (or swap space or, in Windows NT, a pagefile) is a space on a hard disk used as the virtual memory extension of a computer’s real memory (RAM). Having a swap file allows your computer’s operating system to pretend that you have more RAM than you actually do. The least recently used files in RAM can be «swapped out» to your hard disk until they are needed later so that new files can be «swapped in» to RAM. In larger operating systems (such as IBM’s OS/390), the units that are moved are called pages and the swapping is called paging.

One advantage of a swap file is that it can be organized as a single contiguous space so that fewer I/O operations are required to read or write a complete file.

In general, Windows and UNIX-based operating systems provide a default swap file of a certain size that the user or a system administrator can usually change.

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What is swap space in windows

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Question

What is difference between swap space and page file.

I set the page file to 0 MB(No page file) but when I use Everest Software it show 1023 MB swap Space.Is there difference between them?

Answers

Swapping meaning data in and out from memory ie. primary to secondary. Paging is also the same thing, but its mostly used nowadays as virtual memory is based on pages. So, its like pages in and out. Swap space the memory used for swapping entire processes from system memory into the swapfile. Where as paging transfers the pages to page file when the memory is almost full.

Regarding Everest, I think you should check with the supplier.

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What are page and swap files and how big should they be?

By Tom Li 25 March 2018

How to change your virtual memory settings in Windows.

While you probably don’t need to adjust your PC’s page and swap files, it’s useful to know what they are when troubleshooting, or if you’re trying to free up a little hard drive space.

What is a page file?

A page file acts like a physical extension of RAM and is used to offload excess or idle data from the memory to the hard disk. It’s necessary because if the main system RAM is overloaded and no page space is available, a program could crash and potentially lose data.

What is a swap file?

The swap file and the page file perform essentially the same function. Swap files are also a reserved section of disk space that’s used for offloading data from RAM. One of the swap file’s primary functions is to provide a page space for Windows Apps from the Windows Store. When a Windows app enters idle mode, it’s unloaded into the swap file until the user activates it again. This frees up some memory for more important tasks that are currently running.

The swap file co-exists alongside the page file and is much smaller in size, taking up only a few hundred megabytes of space at most. It sits silently in the background and requires no intervention from the user. If you want to check the size of your swap file, it’s listed as swafile.sys in the Windows file tree.

Besides using only a small portion of your disk space, the swap file does not impact performance as long as it’s not being accessed constantly (nor does the page file, for that matter). This typically happens when the system is depleted of actual RAM. If this is happening to you, consider installing more RAM.

On the other hand, if you have oodles of RAM but are desperate for storage space, you can choose to shrink the size of your page file. Below are instructions for changing your page file, and how big it should be.

How do I change the size of my page file?

To change the size of your page file, navigate to the ‘System’ section of the Windows Control Panel. Open ‘Advanced System Settings’ and navigate to the ‘Advanced’ tab. Click the ‘Settings’ button under the ‘Performance’ section to open another window. Click on the new window’s ‘Advanced’ tab, and click ‘Change’ under the ‘Virtual Memory’ section.

There isn’t a way to directly adjust the size of the swap file. If you have a page file enabled on your machine, which you should by default, then Windows will dynamically adjust its size for you.

How big should my page file be?

Initially, Windows will configure a page file size based on the amount of memory installed and free disk space available. If you don’t run memory intensive applications (such as virtual machines and production software) other than games, you can shrink the page file down to a fraction of your total available RAM.

Personally, I have my page file configured to 2GB on a system with 16GB RAM without any issues. For users with 8GB RAM or below, I would recommend keeping the default page size.

You can also choose to disable paging completely, thus maximizing your space savings. I would strongly recommend against this as it could make your system and programs crash when you unexpectedly run out of RAM. Certain critical functions in older versions of Windows, such as a complete memory dump, would not even run with the page file disabled.

What’s the difference between “virtual memory” and “swap space”?

Can any one please make me clear what is the difference between virtual memory and swap space?

And why do we say that for a 32-bit machine the maximum virtual memory accessible is 4 GB only?

5 Answers 5

There’s an excellent explantation of virtual memory over on superuser.

Simply put, virtual memory is a combination of RAM and disk space that running processes can use.

Swap space is the portion of virtual memory that is on the hard disk, used when RAM is full.

As for why 32bit CPU is limited to 4gb virtual memory, it’s addressed well here:

By definition, a 32-bit processor uses 32 bits to refer to the location of each byte of memory. 2^32 = 4.2 billion, which means a memory address that’s 32 bits long can only refer to 4.2 billion unique locations (i.e. 4 GB).

There is some confusion regarding the term Virtual Memory, and it actually refers to the following two very different concepts

1. Using disk pages to extend the conceptual amount of physical memory a computer has — The correct term for this is actually Paging
2. An abstraction used by various OS/CPUs to create the illusion of each process running in a separate contiguous address space.

Swap space, OTOH, is the name of the portion of disk used to store additional RAM pages when not in use.

An important realization to make is that the former is transparently possible due to the hardware and OS support of the latter.

In order to make better sense of all this, you should consider how the «Virtual Memory» (as in definition 2) is supported by the CPU and OS.

Suppose you have a 32 bit pointer (64 bit points are similar, but use slightly different mechanisms). Once «Virtual Memory» has been enabled, the processor considers this pointer to be made as three parts.

• The highest 10 bits are a Page Directory Entry
• The following 10 bits are a Page Table Entry
• The last 12 bits make up the Page Offset

Now, when the CPU tries to access the contents of a pointer, it first consults the Page Directory table — a table consisting of 1024 entries (in the X86 architecture the location of which is pointed to by the CR3 register). The 10 bits Page Directory Entry is an index in this table, which points to the physical location of the Page Table. This, in turn, is another table of 1024 entries each of which is a pointer in physical memory, and several important control bits. (We’ll get back to these later). Once a page has been found, the last 12 bits are used to find an address within that page.

There are many more details (TLBs, Large Pages, PAE, Selectors, Page Protection) but the short explanation above captures the gist of things.

Using this translation mechanism, an OS can use a different set of physical pages for each process, thus giving each process the illusion of having all the memory for itself (as each process gets its own Page Directory)

On top of this Virtual Memory the OS may also add the concept of Paging. One of the control bits discussed earlier allows to specify whether an entry is «Present». If it isn’t present, an attempt to access that entry would result in a Page Fault exception. The OS can capture this exception and act accordingly. OSs supporting swapping/paging can thus decide to load a page from the Swap Space, fix the translation tables, and then issue the memory access again.

This is where the two terms combine, an OS supporting Virtual Memory and Paging can give processes the illusion of having more memory than actually present by paging (swapping) pages in and out of the swap area.

As to your last question (Why is it said 32 bit CPU is limited to 4GB Virtual Memory). This refers to the «Virtual Memory» of definition 2, and is an immediate result of the pointer size. If the CPU can only use 32 bit pointers, you have only 32 bit to express different addresses, this gives you 2^32 = 4GB of addressable memory.