Upgrading & Fixing Laptops DUMmIES

The issue of undeleting a file was a pretty important one: In the original versions

of DOS, it was very easy to make a mistake typing a command or entering a file-

name and erasing your only copy of the Great American Novel. Poof: gone!

And defragmentation, if left untreated, can become a serious problem on a

computer, causing the operating system (or Windows) and programs and

files to open slower and slower and s-l-o-w-e-r to the point where the machine

is almost unusable. I explain the not-all-that-complex concept of fragmenta-

tion and undeleting in the “Cracking fragmentation” sidebar.

A secondary value of defragmentation (and sometimes a primary one) is that

contiguous files are easier to recover in case of corruption to the file attribute

table — the index of filenames and locations maintained by the operating

system. Data recovery programs can find the single file without having to look

for its broken pieces.

290 Part V: The Software Side of Life

Cracking fragmentation

What is fragmentation? Start by considering the

fact that not every file is the same length. You

may write a short note to yourself, and the com-

puter will store it in a space of, say, 64 KB of

space. (The actual minimum size for a file

depends on the size of the disk, the operating

system, and the file management system used

to format the drive.) The next file you store might

be a digitized photo or a song that occupies

3MB (a space 50 times larger than your note).

What happens if you later reopen that short

note and add a few more pages to it? One pos-

sibility is that the note will be split into two

pieces and placed wherever there is a hole.

Another possibility is that first small file will be

“deleted” and a longer, single file will be placed

somewhere else on the disk.

So that brings me to “deleting” a file. You might

think this means the file is physically erased from

the surface of the drive, but to do so would waste

a relatively huge amount of time. Remember that

computers are all about speed. Instead of eras-

ing the file, the hard drive controller changes

the first letter of the filename to a nonstandard

character (such as an %; actually, it uses the

hexadecimal value E5) that the file indexing

system doesn’t recognize. The file is still there,

but the index no longer sees it.

And so the two solutions: A defragmenter

searches the drive for all of the file or program

pieces and then locates an open space to

recopy the pieces into a contiguous stream of

digital information. The first defraggers did

simply that, but later versions used more sophis-

ticated programming to place more commonly

used files in locations where the read/write

heads can more quickly find them.

And the first “undelete” program was basically

as simple as this: It searched the hard drive for

files that began with hexadecimal E5 and then

presented a list of those files. When you found

the one you wanted to save, you instructed the

program to change that nonstandard character

to one that would make the entire file visible to

the operating system. (From such a relatively

simple utility was born the substantial fortune of

Peter Norton, a good-hearted friend of mine

from the early days of the PC.)