Mac OS X was originally presented as the tenth major version of Apple's operating system for Macintosh computers until 2020. The project was first code named ' Rhapsody' and then officially named Mac OS X. This purchase also led to Steve Jobs returning to Apple as an interim, and then the permanent CEO, shepherding the transformation of the programmer-friendly OPENSTEP into a system that would be adopted by Apple's primary market of home users and creative professionals. This led Apple to acquire NeXT in 1997, allowing NeXTSTEP, later called OPENSTEP, to serve as the basis for Apple's next generation operating system. Throughout the early 1990s, Apple had tried to create a 'next-generation' OS to succeed its classic Mac OS through the Taligent, Copland and Gershwin projects, but all were eventually abandoned. Its graphical user interface was built on top of an object-oriented GUI toolkit using the Objective-C programming language. The kernel of NeXTSTEP is based upon the Mach kernel, which was originally developed at Carnegie Mellon University, with additional kernel layers and low-level user space code derived from parts of BSD. There, the Unix-like NeXTSTEP operating system was developed, before being launched in 1989.

The heritage of what would become macOS had originated at NeXT, a company founded by Steve Jobs following his departure from Apple in 1985. As of 2023, the most recent release of macOS is macOS 14 Sonoma. In 2020, Apple began the Apple silicon transition, using self-designed, 64-bit ARM-based Apple M series processors on the latest Macintosh computers. In 2006, Apple transitioned to the Intel architecture with a line of Macs using Intel Core processors. MacOS has supported three major processor architectures, beginning with PowerPC-based Macs in 1999. After sixteen distinct versions of macOS 10, macOS Big Sur was presented as version 11 in 2020, and every subsequent version has also incremented the major version number. Apple shortened the name to 'OS X' in 2011 and then changed it to 'macOS' in 2016 to align with the branding of Apple's other operating systems, iOS, watchOS, and tvOS. The derivatives of macOS are Apple's other operating systems: iOS, iPadOS, watchOS, tvOS, and audioOS.Ī prominent part of macOS's original brand identity was the use of Roman numeral X, pronounced 'ten' as in Mac OS X and also the iPhone X, as well as code naming each release after species of big cats, or places within California. Mac OS X 10.5 Leopard, Mac OS X 10.6 Snow Leopard and all releases from OS X 10.8 Mountain Lion to macOS 14 Sonoma are UNIX 03 certified. The first desktop version, Mac OS X 10.0, was released on March 24, 2001.

During this time, Apple co-founder Steve Jobs had left Apple and started another company, NeXT, developing the NeXTSTEP platform that would later be acquired by Apple to form the basis of macOS. MacOS succeeded the classic Mac OS, a Macintosh operating system from 1984 to 2001. Within the market of desktop and laptop computers, it is the second most widely used desktop OS, after Microsoft Windows and ahead of Linux (including ChromeOS). It is the primary operating system for Apple's Mac computers. That's beyond the scope of this answer, but I'll keep my finger's crossed that it doesn't come to that.MacOS ( / ˌ m æ k oʊ ˈ ɛ s/ previously OS X and originally Mac OS X) is an operating system developed and marketed by Apple Inc. If it refuses to mount for some reason, or you don't see it there at all, then it's unfortunately likely that there's something a bit wrong going on, either with your connection or the drive's hardware. Hopefully the hard drive should start working, and then appear on your Desktop. Can you see your USB drive in there? If so, but it's greyed out, click on it and click the big blue Mount button. In the sidebar, you should see your internal hard drive and any external hard drives you have connected. In Disk Utility, you should have a window with a sidebar inside it. When you see it, hit Enter and let it load. It might pop up before you finish typing. Click on Spotlight, and type in Disk Utility. If not, let's see if it's connected but not mounting. You should now be in a Finder folder called Volumes that contains links to all of your connected drives and mounted disk images. In the window that's dropped down, type in /Volumes/ and hit Enter. If you still don't see anything, make sure Finder in selected, then click on Go, then Go to folder. Now close the Preferences window and check your Desktop and Finder sidebar.

Similarly, click on the Sidebar tab, and tick External disks there. Underneath Show these items on the desktop make sure External Disks is checked. In Finder, click on Finder at the top of the screen, then Preferences.

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