1 First steps So, as a rule of thumb, if you have 1 GB of RAM or more in your host computer, it is usually safe to allocate 512 MB to each VM. But, in any case, make sure you always have at least 256 to 512 MB of RAM left on your host operating system. Otherwise you may cause your host OS to excessively swap out memory to your hard disk, effectively bringing your host system to a standstill. As with the other settings, you can change this setting later, after you have created the VM. 4. Next, you must specify a virtual hard disk for your VM. There are many and potentially complicated ways in which VirtualBox can provide hard disk space to a VM (see chapter 5, Virtual storage, page 71 for details), but the most common way is to use a large image file on your “real” hard disk, whose contents VirtualBox presents to your VM as if it were a complete hard disk. This file represents an entire hard disk then, so you can even copy it to another host and use it with another VirtualBox installation. The wizard shows you the following window: Here you have the following options: • To create a new, empty virtual hard disk, press the “New” button. • You can pick an existing disk image file. The drop-down list presented in the window contains all disk images which are cur- rently remembered by VirtualBox, probably because they are currently attached to a virtual machine (or have been in the past). Alternatively, you can click on the small folder button next to the drop-down list to bring up a standard file dialog, which allows you to pick any disk image file on your host disk. Most probably, if you are using VirtualBox for the first time, you will want to create a new disk image. Hence, press the “New” button. This brings up another window, the “Create New Virtual Disk Wizard”, which helps you create a new disk image file in the new virtual machine’s folder. VirtualBox supports two types of image files: • A dynamically expanding file will only grow in size when the guest actually stores data on its virtual hard disk. It will therefore initially be small on the host hard drive and only later grow to the size specified as it is filled with data. 17