Now that you know what each one does, we can talk about how much storage space you need on it. This will be determined by the following: Your Operating System; Whether or not you have an SSD; The amount of RAM and how often you use your computer. For operating systems, some require more hard drives than others - for example, Mac OS X Lion takes up 40GB of storage space (for a fully installed version) while Windows 7 needs about 18GB for a full installation. If you don't download anything else besides games (which take up many GBs of space) and applications, you won't have to worry about storage. On the other hand, if you do download tons of torrents/p2p programs (which take up more space than a regular application), then high HDD usage is a good thing for your computer. Also, newer operating systems require more hard drive space as they don't work with old versions of Windows/Mac OS - this is why upgrading to Windows 10 would need twice the amount of storage that Win 7 required. If you are planning on having an SSD in your laptop, then there's not much to worry about - The common belief is that although SSDs are faster at loading things like web pages and media files than a hard drive can load them fast enough so it's actually slower to have an SSD. Another reason is that most laptops have a small amount of storage anyway (like the new MacBooks which only have 128GB of storage).