The core of Mac OS X is an open source OS called Darwin , but Darwin can not run Mac OS X software . Releases of Mac OS X are named after big cats : for example , Mac OS X v10 .6 is usually referred to by Apple and users as `` Snow Leopard '' . The server edition , Mac OS X Server , is architecturally identical to its desktop counterpart , and includes tools to facilitate management of workgroups of Mac OS X machines , and to provide access to network services .