Parallels Desktop 4 review

Virtualisation: its benefits are well worn and oft-repeated, as it enables you to run several operating systems side by side and switch between them at will.

Parallels, one of two commercial virtualisation products for the Mac, is a software-based PC replacement that lets you run Windows (or Linux) on your Mac. This will both save you money and help you avoid the electronic waste that manifests itself at the end of a PC's life.

But Parallels is also smarter than a PC, treating Windows as both an operating system and just another application. This means it can be confined to a resizable window on your Desktop, and because Parallels lets you access your files in either operating system from the other, you soon forget you're running two at once.

On installing version 4, it maps your existing folders - Documents, Pictures, Desktop and so on - to their Windows equivalents. That'll set alarm bells ringing for the paranoid, but it comes bundled with security software from Kaspersky and Acronis to help keep you safe. If you don't like sharing data between the two, you can lock off your Mac folders from Windows.

Considering you're running two systems on a single disk, Parallels does a sterling job of managing permissions between the two. You can set default applications for browsing the web, sending emails and reading newsgroups, so that clicking a mailto link in Internet Explorer can open a new message in Mac OS X Mail. Likewise, when you insert a memory key, it won't automatically mount in Windows. Instead, Parallels pops up a dialog asking which operating system you want to see it in.

Version 4 claims a 50% performance hike compared to previous editions, and it certainly felt snappy on our MacBook 2.16GHz with 2GB of Ram. We were able to keep Windows running in Coherence mode, streaming ITV's catch-up service in a Windows window, while simultaneously working on a document in TextEdit under OS X. We didn't dread dipping into Windows to check how a web page looked, and found we could even leave Windows running in the background throughout the day while working predominantly in Mac applications at other times. This is a boon for designers who need to check a project's cross-platform performance as it progresses, rather than saving up all of their changes for a single previewing session at the end of the working day.

If you do work this way, then the shared clipboard and ability to drag and drop between the two environments will soon become second nature. Virtual machines' disks can also be mounted on the Mac Desktop and indexed by Spotlight. Combined, these features largely blur the artificial lines between your host and guest environments.

Parallels now features four viewing modes: Coherence, which runs Windows applications as though they were native Mac tools; Window, which confines the Windows environment to a single application window; Full screen, which speaks for itself; and Modality, which lets you run several virtual machines side-by-side on a single screen.

Window and Modality are by far the most beguiling. Window does something no PC can do: it lets you drag a corner of the Windows environment to resize it and have the Desktop's resolution dynamically resize to fit. You can't do that on hardware, where the aspect ratio will generally fit the shape of the screen. Modality, on the other hand, drops the Parallels toolbar, giving you an operating system in a resizable window that remains surprisingly usable when reduced to a tiny fraction of its original size. Shrinking or expanding the window changes the scale, rather than the resolution in Modality, which effectively lends OS X's zooming features to Windows.