Difference between pages "Windows SuperFetch Format" and "SuperFetch"

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SuperFetch, is a memory management scheme that enhances the least-recently accessed approach with historical information and proactive memory management. [http://technet.microsoft.com/en-us/magazine/2007.03.vistakernel.aspx]
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SuperFetch is a performance enhancement introduced in [[Microsoft]] [[Windows|Windows Vista]] to reduce the time necessary to launch applications. An expanded version of the [[Prefetch]] files found in Windows XP, they record usage scenarios and load resources into memory before they are needed. Those resources can be loaded into physical memory and extra memory provided by [[ReadyBoost]].
  
<b>Note that the following format specification are incomplete.</b>
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== Configuration ==
  
== SuperFetch DB files ==
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Because SuperFetch appears to leave a system with no available memory, some users turn it off to create the appearance of having more free memory. The feature can be configured by changing the <tt>HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\Session Manager\Memory Management\PrefetchParameters\EnableSuperfetch</tt> [[Registry]] key [http://www.codinghorror.com/blog/archives/000688.html]. A value of zero disables SuperFetch, one enables it for booting only, two for applications, and three for both applications and boot. This setting can also be changed using the Services console, <tt>services.msc</tt> [http://tiredblogger.wordpress.com/2007/03/27/superfetch-not-so-super-for-gaming/].
The <tt>Ag*.db</tt> files are of the SuperFetch file format. E.g.
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<pre>
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AgAppLaunch.db
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AgCx_SC*.db
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AgGlFaultHistory.db
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AgGlFgAppHistory.db
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AgGlGlobalHistory.db
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AgGlUAD_%SID%.db
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AgGlUAD_P_%SID%.db
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AgRobust.db
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</pre>
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The SuperFetch DB files can be stored in uncompressed or compressed form, where different version of Windows use different compression methods:
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== File Formats ==
* Compressed SuperFetch DB - MEMO file format; Windows Vista
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* Compressed SuperFetch DB - MEM0 file format; Windows  7
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* Compressed SuperFetch DB - MAM file format; Windows 8
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=== Compressed SuperFetch DB - MEMO file format ===
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Data for SuperFetch is gathered by the <tt>%SystemRoot%\System32\Sysmain.dll</tt>, part of the Service Host process, <tt>%SystemRoot%\System32\Svchost.exe</tt>, and stored in a series of files in the <tt>%SystemRoot%\Prefetch</tt> directory [http://www.microsoft.com/technet/technetmag/issues/2007/03/VistaKernel/]. These files appear to start with the prefix <tt>Ag</tt> and have a <tt>.db</tt> extension. The format of these files is not fully known, there is available unofficial partial specification [http://blog.rewolf.pl/blog/?p=214] and open source (GPL) dumper for .db files [http://code.google.com/p/rewolf-superfetch-dumper/]. Some information can be gleaned from these files by searching for [[Unicode]] [[strings]] in them.
The MEM file consists of:
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* file header
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* compressed blocks
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This format uses the LZNT1 compression method
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The SuperFetch feature is seeded with some basic usage patterns when the operating system is installed [http://channel9.msdn.com/showpost.aspx?postid=242429].
 
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==== File header ====
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The file header is 84 bytes of size and consists of:
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{| class="wikitable"
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|-
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! Offset
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! Size
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! Value
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! Description
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|-
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| 0
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| 4
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| "MEMO" (0x4d, 0x45, 0x4d, 0x4f)
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| Signature
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|-
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| 4
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| 4
+
|
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| Uncompressed (total) data size
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|-
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|}
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=== Compressed SuperFetch DB - MEM0 file format ===
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The MEM file consists of:
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* file header
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* compressed blocks
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This format uses the LZXPRESS Huffman compression method
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==== Compressed blocks ====
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<b>TODO</b>
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==== File header ====
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The file header is 84 bytes of size and consists of:
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{| class="wikitable"
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|-
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! Offset
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! Size
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! Value
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! Description
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|-
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| 0
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| 4
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| "MEM0" (0x4d, 0x45, 0x4d, 0x30)
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| Signature
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|-
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| 4
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| 4
+
|
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| Uncompressed (total) data size
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|-
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|}
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==== Compressed blocks ====
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The file header is followed by compressed blocks:
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{| class="wikitable"
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|-
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! Offset
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! Size
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! Value
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! Description
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|-
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| 0
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| 4
+
|
+
| Compressed data size
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|-
+
| 4
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| ...
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|
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| Compressed data
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|-
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|}
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The uncompressed block size is 65536 (0x10000) or the remaining uncompressed data size for the last block.
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=== Compressed SuperFetch DB - MAM file format ===
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The MAM file consists of:
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* file header
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* compressed blocks
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This format uses the <b>TODO</b> compression method
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==== File header ====
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<b>TODO</b>
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{| class="wikitable"
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|-
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! Offset
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! Size
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! Value
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! Description
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|-
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| 0
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| 4
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| "MAM\x84" (0x4d, 0x41, 0x4d, 0x84)
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| Signature
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|-
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|}
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==== Compressed blocks ====
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<b>TODO</b>
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=== Uncompressed SuperFetch DB format ===
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<b>TODO</b>
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== TRX files ==
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The <tt>Ag*.db.trx</tt> files are of the TRX file format. E.g.
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<pre>
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AgCx_SC*.db.trx
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</pre>
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<b>Note that the following format specification is incomplete.</b>
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=== File header ===
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The file header is variable of size and consists of:
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{| class="wikitable"
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|-
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! Offset
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! Size
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! Value
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! Description
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|-
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| 0
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| 4
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| 1
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| Unknown (Version?)
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|-
+
| 4
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| 4
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|
+
| Unknown
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|-
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| 8
+
| 4
+
|
+
| File size
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|-
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| 12
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| 4
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|
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| Maximum number of records (of the record offsets array)
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|-
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| 16
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| 4
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|
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| Number of records
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|-
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| 20
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| ...
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|
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| Record offsets array, where the record offset is a 32-bit integer. Unused record offset are set to 0.
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|-
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|}
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=== Record ===
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<b>TODO describe</b>
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== See Also ==
 
== See Also ==
* [[SuperFetch]]
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* [[Prefetch]]
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* [[Windows SuperFetch Format|SuperFetch Format]]
 +
* [[Windows]]
  
 
== External Links ==
 
== External Links ==
* [http://technet.microsoft.com/en-us/magazine/2007.03.vistakernel.aspx Inside the Windows Vista Kernel: Part 2], by [[Mark Russinovich]], March 2007
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* [http://en.wikipedia.org/wiki/Windows_Vista_I/O_technologies#SuperFetch Wikipedia: Windows Vista I/O technologies - SuperFetch]
* [http://blog.rewolf.pl/blog/?p=214 Windows SuperFetch file format – partial specification], by ReWolf, October 5, 2011
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* [http://channel9.msdn.com/showpost.aspx?postid=242429 Channel 9 Interview with Michael Fortin of Microsoft on SuperFetch]
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* [http://www.informationweek.com/news/showArticle.jhtml?articleID=196902178 Microsoft Predicts The Future With Vista's SuperFetch] from Information Week
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* [http://jessekornblum.com/presentations/dodcc08-2.pdf DC3 Presentation: My You Look SuperFetching], by Jesse Kornblum
 +
 
 +
== Tools ==
 +
=== Open Source ===
 +
* [https://code.google.com/p/rewolf-superfetch-dumper/ rewolf-superfetch-dumper]
  
[[Category:File Formats]]
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[[Category:Windows]]

Revision as of 15:15, 23 April 2014

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SuperFetch is a performance enhancement introduced in Microsoft Windows Vista to reduce the time necessary to launch applications. An expanded version of the Prefetch files found in Windows XP, they record usage scenarios and load resources into memory before they are needed. Those resources can be loaded into physical memory and extra memory provided by ReadyBoost.

Configuration

Because SuperFetch appears to leave a system with no available memory, some users turn it off to create the appearance of having more free memory. The feature can be configured by changing the HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\Session Manager\Memory Management\PrefetchParameters\EnableSuperfetch Registry key [1]. A value of zero disables SuperFetch, one enables it for booting only, two for applications, and three for both applications and boot. This setting can also be changed using the Services console, services.msc [2].

File Formats

Data for SuperFetch is gathered by the %SystemRoot%\System32\Sysmain.dll, part of the Service Host process, %SystemRoot%\System32\Svchost.exe, and stored in a series of files in the %SystemRoot%\Prefetch directory [3]. These files appear to start with the prefix Ag and have a .db extension. The format of these files is not fully known, there is available unofficial partial specification [4] and open source (GPL) dumper for .db files [5]. Some information can be gleaned from these files by searching for Unicode strings in them.

The SuperFetch feature is seeded with some basic usage patterns when the operating system is installed [6].

See Also

External Links

Tools

Open Source