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

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Windows Prefetch files, introduced in [[Windows|Windows XP]], are designed to speed up the application startup process. Prefetch files contain the name of the executable, a Unicode list of DLLs used by that executable, a count of how many times the executable has been run, and a timestamp indicating the last time the program was run. Although Prefetch is present in Windows 2003, by default it is only enabled for boot prefetching. The feature is also found in [[Windows Vista]], where it has been augmented with [[SuperFetch]], [[ReadyBoot]], and [[ReadyBoost]].
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Up to 128 Prefetch files are stored in the <tt>%SystemRoot%\Prefetch</tt> directory [http://blogs.msdn.com/ryanmy/archive/2005/05/25/421882.aspx]. Each file in that directory should contain the name of the application (up to eight (?) characters), a dash, and then an eight character hash of the location from which that application was run, and a <tt>.pf</tt> extension. The filenames should be all uppercase except for the extension. The format of hashes is not known. A sample filename for [[md5deep]] would look like: <tt>MD5DEEP.EXE-4F89AB0C.pf</tt>. If an application is run from two different locations on the drive (i.e. the user runs <tt>C:\md5deep.exe</tt> and then <tt>C:\Apps\Hashing\md5deep.exe</tt>), there will be two different prefetch files in the Prefetch folder.
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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]
  
 +
<b>Note that the following format specification are incomplete.</b>
  
== Signature ==  
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== SuperFetch DB files ==
Each Prefetch file has a signature in the first 8 bytes of the file. Windows XP will generate Prefetch files with the signature \x11\x00\x00\x00\x53\x43\x43\x41 (0x41434353 0x00000011). Windows 7 and Windows Vista Prefetch file's signature is \x17\x00\x00\x00\x53\x43\x43\x41 (0x41434353 0x00000017). The [http://en.wikipedia.org/wiki/ASCII ASCII] representation of these bytes will display "....SCCA".
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The <tt>Ag*.db</tt> files are of the SuperFetch file format. E.g.
 +
<pre>
 +
AgAppLaunch.db
 +
AgCx_SC*.db
 +
AgGlFaultHistory.db
 +
AgGlFgAppHistory.db
 +
AgGlGlobalHistory.db
 +
AgGlUAD_%SID%.db
 +
AgGlUAD_P_%SID%.db
 +
AgRobust.db
 +
</pre>
  
== Timestamps ==
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The SuperFetch DB files can be stored in uncompressed or compressed form, where different version of Windows use different compressed forms:
 +
* Compressed SuperFetch DB - MEMO file format; Windows Vista
 +
* Compressed SuperFetch DB - MEM0 file format; Windows  7
 +
* Compressed SuperFetch DB - MAM file format; Windows 8
  
Both the [[NTFS]] timestamps for a Prefetch file and the timestamp embedded in each Prefetch file contain valuable information. The timestamp embedded within the Prefetch file is a 64-bit (QWORD) [http://msdn2.microsoft.com/en-us/library/ms724284.aspx FILETIME] object The creation date of the file indicates the first time the application was executed. Both the modification date of the file and the embedded timestamp indicate the last time the application was executed.
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=== Compressed SuperFetch DB - MEMO file format ===
 +
The MEM file consists of:
 +
* file header
 +
* compressed blocks
  
Windows will store timestamps according to Windows [http://msdn.microsoft.com/en-us/library/ms724290%28VS.85%29.aspx epoch].
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This format uses the LZNT1 compression method
  
==== Creation Time ====
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==== File header ====
The creation time does not have a static offset on any Windows platform. The location of the creation time can be found using the offset 0x8 + length of Volume path offset.
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The file header is 84 bytes of size and consists of:
 +
{| class="wikitable"
 +
|-
 +
! Offset
 +
! Size
 +
! Value
 +
! Description
 +
|-
 +
| 0
 +
| 4
 +
| "MEMO" (0x4d, 0x45, 0x4d, 0x4f)
 +
| Signature
 +
|-
 +
| 4
 +
| 4
 +
|
 +
| Uncompressed (total) data size
 +
|-
 +
|}
  
==== Last Run Time ====
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==== Compressed blocks ====
A timestamp of when the application was last ran is embedded into the Prefetch file. The offset to the "Last Run Time" is located at offset 0x78 from the beginning of the file on [[Windows]] XP. The offset for Windows Vista and Windows 7 is at 0x80.  
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The compressed block size is the chunk data size, which is part of the LZNT1 compressed data, + 2 bytes for the size of the chunk header itself.
  
== MetaData ==
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The uncompressed block size is 4096 (0x1000) or the remaining uncompressed data size for the last block.
==== Header ====
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In each Prefetch file, the size of the header is stored and can be found at offset 0x54 on Windows XP, Windows Vista, and Windows 7. The header size for Windows XP is 0x98 (152) and 0xf0 (240) on Windows Vista and Windows 7.
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The Prefetch file will embed the application's name into the header at offset 0x10.
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=== Compressed SuperFetch DB - MEM0 file format ===
 +
The MEM file consists of:
 +
* file header
 +
* compressed blocks
  
==== Run Count ====
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This format uses the LZXPRESS Huffman compression method
The run count, or number of times the application has been run, is a 4-byte (DWORD) value located at offset 0x90 from the beginning of the file on [[Windows]] XP. On Windows Vista and Windows 7, the run time can be found at 0x98.
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==== Volume ====
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==== File header ====
Volume related information, volume path and volume serial number, are embedded into the Prefetch file. The precise offset for this information varies for each application ran. In the header at offset 0x6c, the location of the volume path is stored. The location is a 4-bytes (DWORD) value. The offset 0x6c is consistent for Windows XP and Windows 7.
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The file header is 84 bytes of size and consists of:
 +
{| class="wikitable"
 +
|-
 +
! Offset
 +
! Size
 +
! Value
 +
! Description
 +
|-
 +
| 0
 +
| 4
 +
| "MEM0" (0x4d, 0x45, 0x4d, 0x30)
 +
| Signature
 +
|-
 +
| 4
 +
| 4
 +
|
 +
| Uncompressed (total) data size
 +
|-
 +
|}
  
At the location given from 0ffst 0x6c, a 4 byte value is stored which is the number of bytes from current offset (location from offset 0x6c) to the beginning of the volume path. The location from offset 0x6c, for ease, will be called the "volume path offset." The volume path is embedded as a NULL-terminating string.
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==== Compressed blocks ====
 +
The file header is followed by compressed blocks:
 +
{| class="wikitable"
 +
|-
 +
! Offset
 +
! Size
 +
! Value
 +
! Description
 +
|-
 +
| 0
 +
| 4
 +
|
 +
| Compressed data size
 +
|-
 +
| 4
 +
| ...
 +
|
 +
| Compressed data
 +
|-
 +
|}
  
The length of the volume path is a 4-byte value is located at volume path offset + 0x4.
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The uncompressed block size is 65536 (0x10000) or the remaining uncompressed data size for the last block.
  
The volume [http://en.wikipedia.org/wiki/Volume_serial_number serial number] is a 4-byte value that identifies a media storage. A serial number does not have a consistent offset within a Prefetch between Windows operating systems. The 4-byte value can be found eight (8) bytes from the creation time location. The [http://en.wikipedia.org/wiki/Vol_%28command%29 vol] command on Windows can verify the volume serial number.
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=== Compressed SuperFetch DB - MAM file format ===
 +
The MAM file consists of:
 +
* file header
 +
* compressed blocks
  
==== End of File ====
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This format uses the <b>TODO</b> compression method
The end of file (EOF) for each Prefetch file can be located at offset 0xc.
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 +
==== File header ====
 +
<b>TODO</b>
 +
 
 +
{| class="wikitable"
 +
|-
 +
! Offset
 +
! Size
 +
! Value
 +
! Description
 +
|-
 +
| 0
 +
| 4
 +
| "MAM\x84" (0x4d, 0x41, 0x4d, 0x84)
 +
| Signature
 +
|-
 +
|}
 +
 
 +
==== Compressed blocks ====
 +
<b>TODO</b>
 +
 
 +
=== Uncompressed SuperFetch DB format ===
 +
<b>TODO</b>
 +
 
 +
==== File header ====
 +
<b>TODO</b>
 +
 
 +
{| class="wikitable"
 +
|-
 +
! Offset
 +
! Size
 +
! Value
 +
! Description
 +
|-
 +
| 0
 +
| 4
 +
| 0x0000000e
 +
| Unknown (Database type or signature?)
 +
|-
 +
| 4
 +
| 4
 +
|
 +
| Uncompressed (total) data size
 +
|-
 +
|}
 +
== TRX files ==
 +
The <tt>Ag*.db.trx</tt> files are of the TRX file format. E.g.
 +
<pre>
 +
AgCx_SC*.db.trx
 +
</pre>
 +
 
 +
<b>Note that the following format specification is incomplete.</b>
 +
 
 +
=== File header ===
 +
The file header is variable of size and consists of:
 +
{| class="wikitable"
 +
|-
 +
! Offset
 +
! Size
 +
! Value
 +
! Description
 +
|-
 +
| 0
 +
| 4
 +
| 1
 +
| Unknown (Version?)
 +
|-
 +
| 4
 +
| 4
 +
|
 +
| Unknown
 +
|-
 +
| 8
 +
| 4
 +
|
 +
| File size
 +
|-
 +
| 12
 +
| 4
 +
|
 +
| Maximum number of records (of the record offsets array)
 +
|-
 +
| 16
 +
| 4
 +
|
 +
| Number of records
 +
|-
 +
| 20
 +
| ...
 +
|
 +
| Record offsets array, where the record offset is a 32-bit integer. Unused record offset are set to 0.
 +
|-
 +
|}
 +
 
 +
=== Record ===
 +
<b>TODO describe</b>
  
 
== See Also ==
 
== See Also ==
 
* [[SuperFetch]]
 
* [[SuperFetch]]
* [[Prefetch XML]]
 
  
 
== External Links ==
 
== External Links ==
* [http://milo2012.wordpress.com/2009/10/19/windows-prefetch-folder-tool/ Prefetch-Tool Script] - Python looks Prefetch files up on a web server.
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* [http://technet.microsoft.com/en-us/magazine/2007.03.vistakernel.aspx Inside the Windows Vista Kernel: Part 2], by [[Mark Russinovich]], March 2007
* [http://www.mitec.cz/wfa.html Windows File Analyzer] - Parses Prefetch files, thumbnail databases, shortcuts, index.dat files, and the recycle bin
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* [http://blog.rewolf.pl/blog/?p=214 Windows SuperFetch file format – partial specification], by ReWolf, October 5, 2011
* [http://www.microsoft.com/whdc/driver/kernel/XP_kernel.mspx#ECLAC Microsoft's description of Prefetch when Windows XP was introduced]
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* [http://msdn.microsoft.com/msdnmag/issues/01/12/XPKernel/default.aspx More detail from Microsoft]
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[[Category:File Formats]]
* [http://www.tzworks.net/prototype_page.php?proto_id=1 Windows Prefetch parser] Free tool that can be run on Windows, Linux or Mac OS-X.
+

Revision as of 00:41, 23 April 2014

Information icon.png

Please help to improve this article by expanding it.
Further information might be found on the discussion page.

SuperFetch, is a memory management scheme that enhances the least-recently accessed approach with historical information and proactive memory management. [1]

Note that the following format specification are incomplete.

SuperFetch DB files

The Ag*.db files are of the SuperFetch file format. E.g.

AgAppLaunch.db
AgCx_SC*.db
AgGlFaultHistory.db
AgGlFgAppHistory.db
AgGlGlobalHistory.db
AgGlUAD_%SID%.db
AgGlUAD_P_%SID%.db
AgRobust.db

The SuperFetch DB files can be stored in uncompressed or compressed form, where different version of Windows use different compressed forms:

  • Compressed SuperFetch DB - MEMO file format; Windows Vista
  • Compressed SuperFetch DB - MEM0 file format; Windows 7
  • Compressed SuperFetch DB - MAM file format; Windows 8

Compressed SuperFetch DB - MEMO file format

The MEM file consists of:

  • file header
  • compressed blocks

This format uses the LZNT1 compression method

File header

The file header is 84 bytes of size and consists of:

Offset Size Value Description
0 4 "MEMO" (0x4d, 0x45, 0x4d, 0x4f) Signature
4 4 Uncompressed (total) data size

Compressed blocks

The compressed block size is the chunk data size, which is part of the LZNT1 compressed data, + 2 bytes for the size of the chunk header itself.

The uncompressed block size is 4096 (0x1000) or the remaining uncompressed data size for the last block.

Compressed SuperFetch DB - MEM0 file format

The MEM file consists of:

  • file header
  • compressed blocks

This format uses the LZXPRESS Huffman compression method

File header

The file header is 84 bytes of size and consists of:

Offset Size Value Description
0 4 "MEM0" (0x4d, 0x45, 0x4d, 0x30) Signature
4 4 Uncompressed (total) data size

Compressed blocks

The file header is followed by compressed blocks:

Offset Size Value Description
0 4 Compressed data size
4 ... Compressed data

The uncompressed block size is 65536 (0x10000) or the remaining uncompressed data size for the last block.

Compressed SuperFetch DB - MAM file format

The MAM file consists of:

  • file header
  • compressed blocks

This format uses the TODO compression method

File header

TODO

Offset Size Value Description
0 4 "MAM\x84" (0x4d, 0x41, 0x4d, 0x84) Signature

Compressed blocks

TODO

Uncompressed SuperFetch DB format

TODO

File header

TODO

Offset Size Value Description
0 4 0x0000000e Unknown (Database type or signature?)
4 4 Uncompressed (total) data size

TRX files

The Ag*.db.trx files are of the TRX file format. E.g.

AgCx_SC*.db.trx

Note that the following format specification is incomplete.

File header

The file header is variable of size and consists of:

Offset Size Value Description
0 4 1 Unknown (Version?)
4 4 Unknown
8 4 File size
12 4 Maximum number of records (of the record offsets array)
16 4 Number of records
20 ... Record offsets array, where the record offset is a 32-bit integer. Unused record offset are set to 0.

Record

TODO describe

See Also

External Links