Bottles of Milk


I got a good question some time ago about computing. So I figured to write a small post about it.

If you right-click a file and navigate to the properties window. You’ll notice that the properties window shows 2 sizes.
One is the size and one is the size on disk. The obvious question of this person was: what is the difference?

The best way to explain you is to make a small comparison which involves milk :’).
Imagine that you own a cow and on a bright sunny morning you are milking the cow.
The result is that you’ll have a bucketĀ filled with nice and fresh milk. Now, you ofcourse don’t want to store the milk in the bucket. A bit hard to shove it all in your fridge so you will fill bottles with this milk.

Let’s say that you’ve got 3 liters of milk (I don’t know how much a cow can “produce” so don’t blame me if this doesn’t seem correct) but you only got 2 liter bottles.

Solution? You take 2 bottles, fill one completely and fill one only half. The 3 liter milk is now stored.

The same happens on your hard drive. The hard drive is devided into blocks. But a certain block can only hold a specific amount of data. But just as with the bucket, your file can be bigger than what 1 block can handle, so you’ll need a part of a second block. Which results in the fact, that your file takes more place on your disk than the actual size of the file.

So the size (shown in the properties window) is the actual size of the file and the size on disk is the size of the file + the “empty” part of the block.

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