Computer storage feels like a ripoff, considering you never get quite as much space as it says
on the box. The part of the reason for this is something called overprovisioning. But we're
not going to talk about that today. Not because we're mean, but because we already did a video on
it. But what we are going to talk about today is another sneaky way that your own drives,
the ones in your computer right now, steal space from you. If you bring up the properties box for
any random file on Windows, you'll see a stat called size on disk. And odds are that it'll be
larger than the field that says size. This means basically what it shows. Most files take up more
space than they really need to occupy. But why? The answer has to do with how your computer's
file system stores data. If you're using Windows, its NTFS file system organizes all of its data
into four kilobyte clusters by default. Aside from making your drive delightful and crunchy,
discrete clusters like these serve the important purpose of making it simpler for your system to
keep track of where everything is. In other words, having consistent cluster size reduces the
overhead of your file system. The downside of this is what we call slack space. In this case,
if a file isn't an exact multiple of four kilobytes in size, you're going to have some wasted space,
or slack. You can see this very easily with small Microsoft Word documents, many of which take up
16 kilobytes on your disk, even though the real size might be a few kilobytes less. A few kilobytes
of wasted space here and there might not seem like that big a deal. But given how many small
files are on the typical SSD, it really starts to add up. Not to mention that many of these small
files are system files that Windows needs to run, so it's not like you can just get rid of them.
But the good news here is that slack space is unlikely to have a massive effect on your drive
unless you are really hurting for those last two megabytes. And that four kilobytes is a relatively
small cluster size compared to other file systems, such as one commonly found on USB flash drives.
But with flash drives being smaller than the typical SSD, why the heck do they have bigger
cluster sizes and more wasted space? Although flash drives can use a variety of file systems,
really any file system, XFAT is popular among modern devices. Despite it having a name that
makes it sound more like the next trendy diet. Unlike NTFS, XFAT has clusters of between 32 and
128 kilobytes. Although you might immediately think that that would result in more slack space,
and you would be right, there are some real benefits to arranging the files this way.
Like other file systems, XFAT has to keep track of which clusters are free and which are used.
And this information also takes up space on the drive. So fewer, larger clusters means a smaller
cluster record. As far as the concern about more slack space, it's less of a space hog if you
only have a relatively small number of large files, which is exactly what many kinds of
flash drives are used for, such as the SD cards and cameras that store high resolution images.
XFAT also differs from NTFS in that it doesn't keep a journal. Basically, that's a log of changes
that helps the file system recover in the event of a crash. Journaling takes up precious space,
XFAT doesn't bother with it. Instead, XFAT uses large clusters so that if there's some kind of
unexpected failure, such as yanking the drive out of the USB port while it's busy, chances are a
smaller number of clusters overall will be affected. I guess the moral of today's story is that,
no, the computer storage industry isn't out to rip you off in the way that you think it is,
though I still wouldn't blow 40 bucks on an SSD water block. I can't believe those exist.
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