A user interface is a method of interacting with a particular machine, device or computer programme; in other words human-computer interaction.

The Xerox Alto was the first computer to use a graphical user interface (GUI) in 1973. It was revolutionary and inspired Steve Jobs with the incarnation of the Macintosh in 1984. Mac OS version 1.0 was released on January 24, 1984.

Meanwhile, Microsoft were also keen on the idea of a graphical user interface, wanting to move away from the confusion of the MS-DOS format. They launched Microsoft Windows version 1.0 on 20 November 1985. Since then, both Apple and Microsoft have strived to make their operating systems more intuitive and reliable.

Unlike Microsoft, Apple labels their operating systems as decimalised numbers. Mac OS has gone through ten incarnations: 1, 2, 3, 4, 5, 6, 7, 8, 9 and the current 10 series (currently on version 10.6.2). Interestingly, Apple label their major software releases after big cats, and refer to their current series as Mac OS X (Roman numerals):

• 10.0 Cheetah (released March 24, 2001)
• 10.1 Puma (released September 25, 2001)
  
• 10.2 Jaguar (released August 24, 2002)
  
• 10.3 Panther (released October 24, 2003)
  
• 10.4 Tiger (released April 29, 2005)
  
• 10.5 Leopard (released October 26, 2007)
  
• 10.6 Snow Leopard (released August 28, 2009)
  

All of Apple's releases have featured notable changes and improvements, except Snow Leopard; which was more of a refined Leopard than radical transition that occurred from Tiger to Leopard. Microsoft on the other hand are inconsistent with their operating system names. The most notable releases include the following:

• Windows 95 (released August 24, 1995)
  
• Windows 98 (released June 25, 1998)
  
• Windows XP (released October 25, 2001)
  
• Windows Vista (released January 30, 2007)
  
• Windows 7 (released October 22, 2009)
  

Windows 95 was a revolutionary step up from Windows 3.1, targeting the mass consumer market; Windows 98 was more about refinements and tweaks; Windows XP featured a massive redesign, and adoption of digital media; Windows Vista was a major visual change of the GUI, and a flawed disaster; and Windows 7 is a fined tuned version of Windows Vista, regarded as the best ever operating system Microsoft have produced.

So what are the worst user interfaces? An obvious choice, Windows Vista. It was incredibly bloated, slow, full of bugs, and riddled with incompatibilities. It is now improved after two service packs, but was rushed and should never have been released as early as it was. Actually, I can't name one Microsoft operating system that hasn't crashed numerous times!

"Any operating system that provokes a campaign for it's predecessor's reintroduction deserves to be classed as terrible technology."
Nate Lanxson (Windows Vista)

So, what are the best user interfaces? My personal favourite is Apple's Snow Leopard. It is beautiful to look at, fast, reliable, and incredibly intuitive. In fact Snow Leopard is so good it makes you look at Windows in a different light; picking out every possible fault you can.