You may have files that took up hundreds of different places on the hard drive, and trying to read them was quite a chore. You see, then things would actually slow down as files got more and more fragmented. Especially in the old days, when hard drives were smaller, and before the introduction of Mac OS X Extended File Format. So it may determine that purple is used more than the yellow file is, so it may put that first, earlier on the hard disk, where it's easier and quicker to access. It may go ahead and rearrange the files completely to optimize them. Matter of fact, it may even do more than that.

So all the free space is after the files. It would actually move all the files, so it would move yellow up, taking up those two spaces there, and move purple right after it. Matter of fact, it would do even more than that.

So we can defrag, and what that would do, basically, is move those two blocks so purple is all together. So, you can see how the purple file is now divided up into two parts. Now what used to happen is the hard drive would put the beginning of the file in the first free space it could find you can see those two purple blocks there and then you would end up with the rest of the file in the rest of the free space. Now let's say we want to write a new file. And we still have the red and yellow file there.

Now, what happens if we delete the green file? Now we freed up those two blocks, so they're grey again. The first one's represented by the red blocks, and then there's a small one represented by green blocks, and then a larger one by the yellow. But let's say we write three files to the drive. Okay, so let's say these grey blocks represent blocks of data on your hard drive. Defragmenting it means it takes all the parts of a single file and places it on just one part of the hard drive. A large file may actually be written to different parts of the hard drive. You see, files on a hard drive don't exist just in one spot. And basically what it means is to take your hard drive and optimize it. So, if you're not familiar with the term, defrag is short for defragment. On today's episode, let's find out of you need to defrag your Mac hard drive. Video Transcript: Hi, this is Gary with MacMost Now.

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