Win XP, Compress Files: What does it do?

[Nehmo Sergheyev]

In Windows XP Home (SP1) NTFS file system

In Explorer, when you rightclick on a folder > Properties > you see two
numbers for file size:

Size:
Size on disk:

If you then click on Advanced > (Advanced Attributes dialog box opens)
check the checkbox: Compress contents to save disk space > OK > Apply >
check Apply changes to this folder, subfolder and files > OK

Then the "Size on disk" number lowers - In a graphics folder I just
tried, 6% smaller - and the names of the files now display in blue.

So what is actually happening? How is XP compressing the files? What
does "Size on disk" actually mean? Is there any disadvantage to this
compression?

 

[dev]

Nehmo Sergheyev said:

In Windows XP Home (SP1) NTFS file system

In Explorer, when you rightclick on a folder > Properties > you see two
numbers for file size:

Size:
Size on disk:

If you then click on Advanced > (Advanced Attributes dialog box opens)
check the checkbox: Compress contents to save disk space > OK > Apply >
check Apply changes to this folder, subfolder and files > OK

Then the "Size on disk" number lowers - In a graphics folder I just
tried, 6% smaller - and the names of the files now display in blue.

So what is actually happening? How is XP compressing the files? What
does "Size on disk" actually mean? Is there any disadvantage to this
compression?

The process compacts the files, which then display in blue. This saves
disk space, but is little needed these days, owing to inexpensive harddisk
storage. See HELP & SUPPORT for more info. Type "compress files" into
the search box.

 

[Thorsten Matzner]

So what is actually happening? How is XP compressing the files? What
does "Size on disk" actually mean? Is there any disadvantage to this
compression?

This may help: "HOW TO: Use File Compression in Windows XP"
(http://support.microsoft.com/?kbid=307987).