With the unveiling of Lion just days away it is easy to look back at past releases of Mac OS and see how we arrived at Apple’s latest system software. Over the last 27 years Apple has introduced more than 17 major releases of its premier desktop operating system. Some releases such as System 7, and Mac OS X 10.4 Tiger brought revolutionary changes to the Mac while making the transition between hardware architectures. Evolutionary releases like System 6, and Mac OS X 10.6 Snow Leopard consolidated features while improving stability. The entire history of Mac OS says more about Apple than any other product, and it is the best of Mac OS that says the most about Apple’s future.

When considering the best version of Mac OS you must compare releases that offered the greatest number of new features against versions that clocked the longest up time. You must reference the classic system software of yesterday’s Macintosh against the latest breaking developments in Mac OS X. Your answer might be swayed by the first version you ever used, or the operating system that shipped with your first Mac. The best Mac OS is as much a personal question as it is a technical comparison. There is no right choice and it is often our own experiences and requirements that dictate our answer.

It is popular to assume that the latest technology is always the greatest, and this is often true for operating systems where the most recent versions have the most features. But features alone do not make great operating systems, and all Macs cannot run the latest OS. So instead of picking the most stable Mac OS with the most features I choose four versions that span the entire Macintosh product line and provide the best user experience Apple has to offer.

System 6

System 6 was the first widely available Macintosh operating system to be given a unified “Macintosh System Software” version number. From System 6 forward, the Finder would have a version number closely matching that of the System, alleviating much of the confusion caused by the often considerable differences found on earlier Systems.

System 6 oversaw the introduction of the Motorola 68030 processor, the 1.44 MB SuperDrive, and the legendary Macintosh SE30. Later, it would include support for the first specialized laptop features with the introduction of the Macintosh Portable. System 6’s most remarkable feature was cooperative multitasking by way of a optional system extension called MultiFinder.

Multifinder gave each application CPU time, it provided a way for windows from different applications to co-exist by using an application layering model. When an application was activated, all of its windows were brought forward as a single layer. This approach was necessary for backward compatibility, but MultiFinder combined with System 6’s limited 24 bits of addressable RAM introduced many of the memory management problems that would plague Mac OS until the introduction of Mac OS X.

Despite the memory management issues it introduced, System 6 is a favorite among 68k Mac fans for its small memory footprint, and minimalist appeal. It installs from two floppies, uses 600k of RAM, and doesn’t require an additional hard disk. 6.0.8. the final version of System 6 not only consolidated the existing Macintosh System Software, but incorporated important features from System 7 like TrueType fonts, andQuicktime. With MultiFinder turned off System 6 was easily the most stable operating system for classic Macintosh and became a important comparison against the instabilities of System 7.

Mac OS 8

Codename Tempo, Mac OS 8.0 began life as Mac OS 7.7 but was renumbered 8 to exploit a legal loophole shutting down the Macintosh clone market. Mac OS 8 saw the introduction of many new features such as a customizable appearance, contextual menus, pop-up windows, spring-loaded folders, live scrolling, WindowShade, a multithreaded Finder, and desktop pictures. Despite all of these significant usability advances, Mac OS 8’s most important improvements came in later point releases.

Mac OS 8.1 introduced a new file system known as HFS+, which supported large file sizes and made more efficient use of larger hard drives by using a smaller block size. Mac OS 8.5 focused on speed and stability by eliminating 68k support, and requiring a PowerPC processor. Mac OS 8.6 added a new nanokernel making it the most stable classic Mac OS for PowerPC machines.

Mac OS 8 oversaw the introduction of the G3, the iMac, the iBook, and the Power Mac G4. It added a number of features from the abandoned en.wikipedia.orgwikiCopland_(operating_system text: Copland) project, and kept Mac OS moving forward during a difficult time for Apple. Mac OS 9 might be commonly remembered as the last classic Mac OS, but it was a transitional release that traded stability for features and Mac OS X compatibility. Mac OS 8 was the Mac OS that saved Apple.

Mac OS X 10.4 Tiger

I had a tough time picking a best Mac OS between Jaguar, Panther, and Tiger. Mac OS X 10.2 Jaguar brought Mac OS X’s feature-set up to par with Mac OS 9 making Mac OS X usable for a wider audience. Mac OS X 10.3 Panther improved upon Jaguar with faster speeds, while retaining Jaguar’s minimal system requirements. Mac OS X 10.4 Tiger ushered in a new era for Mac OS X by implementing exciting new features, and moving the Mac from PowerPC to Intel based processors. If Tiger wasn’t also the best Mac OS for modern PowerPC Macs I would have a hard time recommending it. I am weary of OS upgrades that try to do too much, and the transition from PowerPC to Intel would have been a monumental leap for most OSes, but Tiger pulled it off with ease. I will always have a soft spot for Panther, the last Mac OS before Apple’s popularity exploded, but Tiger is the undisputed favorite on Twitter.

Tiger removed support for the original iMac and iBook, and required 256MBs of RAM, twice the memory as previous versions of Mac OS X. All other system requirements were the same, although to take full advantage of Core Image a graphics card with 64 MBs of video RAM was required. Tiger didn’t ask a lot from its users but it gave a lot in return.

Automator, Grapher, Dictionary, Quartz Composer, AU Lab, and Dashboard were all brand new applications introduced in Tiger. iChat AV, Safari, Mail, and Quicktime all saw significant updates. With Tiger scripting became easier, graphics transitions and effects were more fluid, real-time audio processing was possible. Definitions, weather, stock market information, flight tracking, and built-in RSS were available at the push of a button. Spotlight, Tiger’s new contextual search engine, brought the contents of your hard drive to the forefront with only a few simple keystrokes. And Quicktime 7 combined with H.264 and iChat AV made video conferencing available for the rest of us.

Almost all of these features were made possible by architecture changes first implemented in Tiger. A 64-bit aware kernel allowed for more memory to be available for individual processes running on a Mac with a 64-bit processor. Launchd modernized Mac OS X’s Unix underpinning and allowed for faster startup. Core Image, Core Video, and Core Audio made all of Tiger’s whiz-bang graphical and audio effects possible, while Core Data made it easier for developers to handle structured data in their applications.

On top of all these new applications and technologies Tiger made the transition from PowerPC to Intel in less than 30 months. It took System 7 almost 7 years to make the switch from 68k to PowerPC. It comes at no surprise that Mac OS X 10.4 Tiger is one of the best selling versions of Mac OS X to date, and one of the best versions of Mac OS ever.

Mac OS X 10.6 Snow Leopard

Snow Leopard is my favorite version of Mac OS X not because of the features it added, but because of the ones it took away. Snow Leopard only runs on Macs with Intel processors. It was the first Mac OS release since System 7.1.1 that does not support the PowerPC architecture (although PowerPC applications are supported via Rosetta , an optional install. Shedding all of those Universal Binaries), and adopting an advanced application compression scheme means Snow Leopard saves 6 GBs of disk space over its predecessor 10.5.

Among Snow Leopard’s select new features are a updated Finder rewritten in Cocoa. A new version of Safari that includes a 50{493f798df480ad5a2796e65210fbf6e65215ebdcc2070f4d9b100f3865a5d00d} increase in JavaScript performance, and support for Microsoft Exchange in Mail, iCal, and Address Book. Under the hood Snow Leopard is the first Mac OS to ship with a 64-bit kernel that can take advantage of greater amounts of memory. QuickTime was completely rewritten to take advantage of audio video codecs in 64-bit, and Grand Central Dispatch was invented to ease the development of applications with multi-core support.

Visually 10.6 Snow Leopard is not much different from 10.5 Leopard. The operating systems looks and acts the same, but in addition to PowerPC support some features have been removed. AppleTalk, Creator Codes, and Classic HFS write access are the most glaring omissions for long time Mac users, but I wouldn’t have Snow Leopard any other way. By making the tough choices and trading features for stability, Snow Leopard is more than a best of breed operating system it is the foundation for the future of Mac OS.

Lion is right around the corner. Built from the best of Mac OS it combines the stability and refinement of Snow Leopard with the usability innovations first seen on the iPhone. It has yet to be determined if the multitouch gestures and full screen apps will be a success on the desktop, and if Lion will be one of the best of Mac OS. All that is certain is that Apple is not standing still, and Lion for better or worse is the future of Mac OS. Let’s hope it will be a good one.