$MachineType is a string giving the general type of computer on which Mathematica is being run.
$MachineType is intended to reflect general families of hardware rather than specific models.
Typical values are "PC", "Macintosh", "Sun", "DEC" and "SGI".
Computers with the same $MachineType may not be binary compatible.
See Section 2.14.5.
See also: $ProcessorType, $OperatingSystem, $System.
New in Version 2.