I want to free up space on my hard disk drive but I can't seem to get an accurate account of its used capacity. The computer says I'm using 87.2 gigabytes of 97.72GB of available capacity on what is supposed to be a 100GB hard drive. I do plenty of video editing and my calculations show 81.42GB of capacity used. What's going on?\nJennifer Deayton, Mid-Levels DQ: A hard disk drive must first be formatted, or initialised, so a user can find and access data stored in the device. Depending on the computer hardware and its operating system, the hard disk drive is typically divided into discrete sectors. Each sector holds a specific amount of data, usually 512 bytes, but it can vary. If you create a document totalling 520 bytes, its storage space will take up two sectors, or 1,024 bytes. The operating system will tell you two sectors are used, even though only a tiny portion of the second is occupied by the data. You will also be informed of the total number of bytes of data in your hard disk and the total disk capacity used. That amount will always be greater than the amount of data being stored. The reason your hard drive is not exactly 100GB in size is because the formatting process takes up quite a bit of space. If you use your computer mainly for editing video, it is clear you need a lot more space. Running your hard drive at nearly 90 per cent capacity will present all kinds of problems. You can afford to get a lot more storage capacity, especially with an external drive, because hard disks are cheap. I want a netbook that is simple to use. Should I get one with Microsoft's Windows operating system or with Linux?\nName and address supplied DQ: As last month's Post Magazine article on mini-notebooks pointed out, you should exercise caution when choosing a netbook. Most models have either Windows - typically, Windows XP - or a version of Linux as their operating system. If you can wait a few months, Microsoft's Windows 7 is designed to run on all netbooks, many of which lack the horsepower to run the Vista platform. Linux is free but, if you are not familiar with the platform, you'd be advised to determine whether you are computer-savvy enough to handle it. I strongly suggest using a netbook with an operating system you feel comfortable with.