At 08:11 PM 11/17/2005, you wrote:
>Does compressing data alter the record?  If so wouldn't this mean
>that other compression methods are altering data?  Even if it does
>alter the data can it be reversed?  I know compression changes the
>size, but not the information as far as I know.

There are different types of compression, some of which (lossy) alter
the data they are compressing by throwing out the "least necessary"
data. Mostly, this is used with images (jpeg is an example), or audio
data (mp3).

Most documents / text etc. are would not work well this way, and so
use lossless compression methods.

I'm not aware of any methods of reversing lossy compression.

Data can be altered in other ways, such as metadata - creation dates,
last access dates, author information, etc. Some methods of
compressions and archiving will touch or discard some of these, some
are more mindful of preserving them. It may be as important to know
when a document was authored, versus just the contents of it. When
you uncompress something, if may show up with a creation/access date
equal to the time you uncompressed it.

However, even just moving the data off a hard drive will make some
information unavailable. Hard drives will contain information on
deleted files, file fragments, and data in the slack space of files.
Files that might not be considered for backing up (such as system
files) may contain data about the last time the computer was used,
what web sites were visited, who used the computer.

Depending on your regulatory needs, keeping the hard drives might be
a good (or possibly required) idea. However, if you don't need /
aren't required to keep that information, getting rid of the hard
drives - as in completely wiping them or better yet, shredding them -
may prevent later expenses.


--
Michael Edwards

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