Head to Head: Parallels Desktop 7 vs VMware Fusion 4

The inclusion of Boot Camp in Mac OS X means that every Mac can also be a Windows PC, at least for those happy to use just one operating system at a time, with a reboot in between and limited access to shared data. For everyone else, virtualisation is a better solution. This is especially true if you want to use an older version of Windows with Lion Lion's version of Boot Camp only supports Windows 7.

Virtualisation is a better solution especially true if you want to use an older version of Windows with Lion Lion's version of Boot Camp only supports Windows 7.

Parallels Desktop and VMWare Fusion are the two leading Mac virtualisation applications, and both recently received major version updates within days of each other. Both list Lion-friendly features, support for virtual Lion machines and a host of other incremental improvements on their respective what's new' pages, but the claims of dramatically increased performance are of more interest to most potential users. What neither party mentions, of course, is how their respective products stack up against each other, but that's where we come in.

What is virtualisation?

Virtualisation allows a self-contained virtual machine' or VM, complete with its own operating system and other software, to run on a computer as if it was just another application. This is nothing new and another technique called emulation has long allowed one operating system to run programs designed for another. Emulation, however, mimics the guest' computer's hardware using software alone, which is sufficient for old computers like the ZX Spectrum, but nowhere near fast enough for a PC running Windows.

Virtualisation, on the other hand, runs the guest computer directly on the host's hardware, giving a significant performance advantage (depending on the host's specification). Better still, the abstracted hardware the virtualisation application presents to the guest operating system is both fixed and independent to the host's, which means a virtual machine can be moved from host to host with no ill effect.

Virtualisation of PC hardware on Macs is only possible because of Apple's 2006 switch to Intel processors. Non-server versions of Windows will only run on x86-compatible chips, which means pre-2006 Macs with PowerPC processors could only run Microsoft's operating system via emulation. With Intel inside, virtualisation suddenly became possible and Parallels Desktop was the first application to exploit this new feature that same year. VMWare Fusion appeared the following year. Although Parallels Desktop has seen more major releases in the meantime, both applications now have a very similar set of features.