Alternate Data Streams

In my recent Operating Systems class, I was supposed to give a 15 minute presentation about the windows file system. Instead of talking only about that, I got permission to talk about alternate data streams. This is my presentation (yes, somewhat short and brief, but I think it still gives a good description of why/how alternate data streams work).

Alternate Data Streams

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A good part of my presentation was doing live demonstrations of how alternate data streams can be used from the command line. Here are some examples:

C:\ads>echo >stream.txt default unnamed data stream

C:\ads>dir
 Volume in drive C is BLAH
 Volume Serial Number is 48C7-9ED4

 Directory of C:\ads

08/15/2009  07:37 AM    <DIR>          .
08/15/2009  07:37 AM    <DIR>          ..
08/15/2009  07:37 AM                30 stream.txt
               1 File(s)             30 bytes
               2 Dir(s)  17,025,347,584 bytes free

C:\ads>more < stream.txt
 default unnamed data stream

C:\ads>echo >stream.txt:ads alternate (named) data stream

C:\ads>dir
 Volume in drive C is BLAH
 Volume Serial Number is 48C7-9ED4

 Directory of C:\ads

08/15/2009  07:37 AM    <DIR>          .
08/15/2009  07:37 AM    <DIR>          ..
08/15/2009  07:38 AM                30 stream.txt
               1 File(s)             30 bytes
               2 Dir(s)  17,025,347,584 bytes free

C:\ads>more < stream.txt:ads
 alternate (named) data stream

C:\ads>type C:\WINDOWS\notepad.exe > stream.txt:other_notepad.exe

C:\ads>start C:\ads\stream.txt:other_notepad.exe

C:\ads>cd ..

C:\>echo >ads:folder_data_stream folders can have named data streams as well

C:\>more <ads:folder_data_stream
 folders can have named data streams as well

C:\>dir ads
 Volume in drive C is BLAH
 Volume Serial Number is 48C7-9ED4

 Directory of C:\ads

08/15/2009  07:39 AM    <DIR>          .
08/15/2009  07:39 AM    <DIR>          ..
08/15/2009  07:38 AM                30 stream.txt
               1 File(s)             30 bytes
               2 Dir(s)  17,024,843,776 bytes free

C:\>dir /a:d ad?
 Volume in drive C is BLAH
 Volume Serial Number is 48C7-9ED4

 Directory of C:\

08/15/2009  07:39 AM    <DIR>          ads
               0 File(s)              0 bytes
               1 Dir(s)  17,024,843,776 bytes free

C:\>