Benefits of defragmenting your computer hard drive

It’s been a long time since I’ve seen someone explain the benefits of defragmenting your computer hard drive. I do see a lot of misconceptions out there. I explained defragmenting in my 1999 book, so I’ll explain it again.

Part of the misconception is that things have changed. The tools have changed, yes. But the need hasn’t.

The caveat

First things first: Defragmenting applies to traditional magnetic hard drives. Solid-state drives, which are high speed drives that use memory chips, don’t benefit as much from defragmenting and defragmenting can cut down on their life expectancy.

SSDs have super-low seek times, so they benefit very little from defragmenting. The built-in Windows defragmenter senses solid state drives and doesn’t actually defragment them.

But hard drives need it desperately, for reasons I’m about to explain.

Benefits of defragmenting explained

This hard drive is a mess. Seeing before and after shots helps explain the benefits of defragmenting.
Here’s a hard drive being defragmented by Puran Defrag. The red blocks are fragmented files. Access to these files is slower than it could be.

Imagine you’re reading a book. Now imagine if the pages were out of order. Instead of just turning a page, you’d have to flip through the book to find the next page you’re supposed to read. It would really increase the amount of time it takes to read a book.

Now imagine if the pages were scattered not just within a single book, but within multiple books.

So what does defragmenting do? Defragmenting is the equivalent of pulling those books apart, reordering the pages properly, and putting them back together. Only instead of rearranging the pages of books, it’s rearranging clusters of data on the disk. It takes some time to do, but in the long run, it’s worth it.

One of the biggest benefits of defragmenting your computer hard drive is that files load much more quickly if the computer doesn’t have to piece it together. A computer can seek much faster than a human can turn a page, but it’s still much faster to just read the file in order.

Hard drives get faster generation over generation, but they still lag far behind memory and CPU speed. Hard drives are still the biggest bottleneck. The slower your hard drive, the slower your computer feels. Occasional defragmenting helps keep your system at peak performance. You’ll notice the difference, so defragmenting is worth it.

Why fragmentation happens

When your computer writes a file to disk, it goes into available empty space. On a freshly formatted disk, there’s probably plenty of contiguous empty space available. But on a crowded disk, the file may have to be split up among multiple empty spaces. If the file ever gets changed, those later changes may end up in a non-contiguous space.

Modern operating systems were designed to not get fragmented as badly as the operating systems from 20 years ago, but those changes didn’t completely eliminate the problem. That’s why defragmenting is still necessary.

The defragmenter you use matters

Good defragmenting software is important, and not all of it is good. Windows has a built-in disk defragmenter. It’s not very good, because it’s based on Diskeeper, which isn’t very good. Both of those defragmenters take an all-or-nothing approach. If they can’t defragment a file completely, they leave it alone. I’d rather do the best job I can. I’d rather leave a file in three pieces than in 30.

My favorite defragmenter was a free program called My Defrag. It’s discontinued, sadly, but many file repositories still have copies of it. Run it about half as often as the documentation recommends and you’ll be in nice shape.

If you’re OK with a commercial solution, Puran Defrag is free for home use. I like its option to defrag during bootup to quickly eliminate fragmented files, but I’d follow up with My Defrag to reorder the files.

Boot time defragmentation

The benefits of defragmenting are clear after boot-time defrag
Here’s a what a drive looks like after running Puran Defrag at boot time. Note there are only two files still fragmented. Following up with another defragmenter might help a bit more.

Defragmenting takes a while. By “a while,” I mean the time varies, but it could be hours. Some defragmenters include the option to run before the system finishes booting. This is much faster, since nothing else is competing for disk access, and nothing is modifying any files.

If you’re trying to defragment a system and it’s taking forever, try a defragmenter like Puran Defrag that can run during boot time. You can let it do the heavy lifting and then follow up with a defragmenter you like better.

File placement

Disk drives are fastest at the front of the disk, due to geometry. One revolution covers more ground at the front than at the back. So a good defragmenter will do file reordering, not just simple defragmentation. With intelligent file reordering, speed-sensitive files like EXE and DLL files migrate to the front of the disk. Files like MP3s that play fine even off the slow part of the disk migrate to the back. Ideally, you’ll put some free space in the zones in between so new files have lots of room and the disk won’t get fragmented again quickly.

I find that when you use a defragmenter with intelligent file placement, you don’t have to defragment very often. Quarterly or even yearly is usually sufficient.

Defragmenting too often does seem to cause more problems than it solves. Way back when I did desktop support, one of my colleagues scheduled computers to defragment every day. I just defragmented when a computer was slow and annoying. I rarely had hard drives go bad but it seemed like he was always swapping drives. Reliability is an area of interest for me.

Other speedup tips

Defragmentation benefits include, most notably, a faster performing system. If you’re interested in other things to do to improve system performance, I have plenty of tips on speeding up Windows 10 if you need them.


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