After the code name 'Jaguar' for version 10.2 received publicity in the media, Apple began openly using the names to promote the operating system: 10.3 was marketed as 'Panther', 10.4 as 'Tiger', 10.5 as 'Leopard', 10.6 as 'Snow Leopard', 10.7 as 'Lion', and 10.8 as 'Mountain Lion'. Prior to its release, version 10.0 was code named 'Cheetah' internally at Apple, and version 10.1 was code named internally as 'Puma'.
With the exception of Mac OS X Server 1.0 and the original public beta, the first several macOS versions were named after big cats. The development of Aqua was delayed somewhat by the switch from OpenStep's Display PostScript engine to one developed in-house that was free of any license restrictions, known as Quartz.
Despite this, OS X maintained a substantial degree of consistency with the traditional Mac OS interface and Apple's own Apple Human Interface Guidelines, with its pull-down menu at the top of the screen, familiar keyboard shortcuts, and support for a single-button mouse. A key new feature was the Dock, an application launcher which took advantage of these capabilities.
Aqua was a substantial departure from the Mac OS 9 interface, which had evolved with little change from that of the original Macintosh operating system: it incorporated full color scalable graphics, anti-aliasing of text and graphics, simulated shading and highlights, transparency and shadows, and animation. The first release of the new OS - Mac OS X Server 1.0 - used a modified version of the Mac OS GUI, but all client versions starting with Mac OS X Developer Preview 3 used a new theme known as Aqua. Support for C, C++, Objective-C, Java, and Python were added, furthering developer comfort with the new platform.
Meanwhile, applications written using the older toolkits would be supported using the 'Classic' Mac OS 9 environment. Mac OS applications could be ported to Carbon without the need for a complete re-write, making them operate as native applications on the new operating system. Over the next two years, major effort was applied to porting the original Macintosh APIs to Unix libraries known as Carbon. When Jobs announced at the World Wide Developer's Conference that what developers really wanted was a modern version of the Mac OS, and Apple was going to deliver it, he was met with thunderous applause. The board asked Steve Jobs to lead the company on an interim basis, essentially giving him carte blanche to make changes to return the company to profitability.
Macs below that can't install Snow Leopard directly may be able to do so via virtualization, as described by this tip.Apple's financial losses continued and the board of directors lost confidence in CEO Gil Amelio, asking him to resign. The Macs listed here that won't run Snow Leopard also are not able to use the retail Lion installer USB Flash drive, and must use the instructions onMacworld to create a specialty Flash drive or be cloned onto another hard drive before their prebundled hard drive dies, to be able to restore Lion.
Lion prebundled Macs thankfully can run Windows in virtualization, which would allow them to use the Windows version of software that may only run in Snow Leopard and earlier on Mac OS X. The Macs below which can only run Lion and later, are also known as Lion prebundled Macs. A second internal or external hard drive can boot into a separate operating system on the same Macs. Partitioning requires an erase of the hard drive. Together with partitioning, the Core2Duo (not CoreDuo, not CoreSolo), Xeon, Core i3, i5, i7 Macs which are Snow Leopard compatible can run both Snow Leopard and Lion, provided they have at least 2 GB of RAM. Older Macs indicated below can use the 10.6.3 retail installer, if not the 10.6 retail installer, if they are older than August 28, 2009. Machine ID is in Apple menu -> About This Mac -> More info (on 10.7 and later the About Window has System Information instead of More info to access the System Profiler) under the hardware section. You can find out which gray installer disc came with Macs that can install Snow Leopard newer than Maby reading.