Computer Document Management

2009-12-01T06:58:00.000-08:00

I have been asked how computers manage files and their deletion. This is a simple question, but the answer is fairly elaborate to really understand the mechanics. These underlaying concepts are necessary to really understand how various software programs cooperate and it is really quite uniform.

Photographs and text documents are stored in files and a basic function of any software program is to manage files created by it and other programs. One of the first things a program needs to know is what formatting the file uses to store a document. A document can be anything: letter, photo, image, etc. The way a program knows the format of a file is its extension (filename.extension). For example, myletter.doc could be the name of a Microsoft Word document.

Files are organized into directories and subdirectories because it would be impossible to manage all the files if they were stored together. These are stored on mechanical devices like hard drives. The main drive is designated as "C". Just to keep things from getting confused there is a colon ":" inserted after the drive designation, for example "C:". Directories and subdirectories are separated by a forward slash "/" or a "\" depending on the operating system. A complete example is: C:\Documents and Settings\Owner\Documents\Veterans Administration\Sepulveda Aug 14, 2006.doc. In this case, if you click on the file name, Windows knows to display the document using Microsoft Word.

Note that the latest version of Microsoft Word saves text files with a "docx" extension as default and can not be opened with older versions of Word. However, it can be forced to save in a "doc" format.

When you use programs like Windows Explorer you will not see anything like the example above because many programs format and separate the parts of the complete directory name to reduce confusion, but it will be familiar to those familiar with DOS. Although this provides a good conceptual idea of how files are arranged into directories it does not explain the mechanics which are necessary to understand what happens when you delete a file and empty the trashcan.

Just to keep things physically manageable, Windows organizes a hard drive into segments, often 4096 bytes. A segment on a hard drive is a section managed by the operating system like Windows. The size varies based on Windows version and disk size, but the size used on your computer is not critical to your conceptual understanding. Some files are larger than others are and will need more than one segment. Windows will allocate these segments when a file is saved from a pool of "free space" that it manages.

When you delete a file it goes into the trashcan which is an icon representing deleted files. If you make a mistake and delete a file by error, you can undelete a file and restore it to its original directory. Years ago I deleted a file before there was undelete capability and I spent hours retyping the program. Today when you delete a file, the original data is retained in the trashcan.

When you empty the trashcan the file's segments are added to the Windows "free space" and are available to be reused by windows to store new files. Large files use several segments linked together like sausages and this relationship is lost when the segments are added to the "free space". However, the bit pattern representing the data in the file is retained on each segment.

Special programs can erase segments that are in the "free space", They will set all the bits in "free space" segments to "0" eliminating data in the segments. However, very weak magnetic patterns may be recoverable from a disk using electronic tools designed specifically for this purpose. This should not be a concern unless someone is doing something illegal.

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2009-01-03T05:38:00.000-08:00

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