iMac G5/1.8 20-Inch

The MPN (Marketing Part Number), also sometimes called the model number, marketing number, order number or part number. This is the part number under which Apple sold this particular Mac model. Only base configurations have part numbers, while Macs sold with various build to order/configure to order options do not have them. What we consider a single Mac may have multiple part numbers, which may refer to different specifications of RAM, drive size, or case colour that were offered as base options. Part numbers also differ by country or region.

In modern Macs it is usually an 8 or 9 digit code, with the last 2 characters being "/A" or occasionally "/B". The one or two characters immediately before the "/" depend on country or region - "B" is the UK, "LL" the USA, etc. We represent this portion as "xx".

EMC numbers cover a narrow group of Macs, or sometimes an individual machine. There are exceptions, but usually models that share an EMC number were released at the same time, and share all attributes apart from minor differences in CPU and other internal components. In a very few cases, Macs of the same model were sold with multiple different EMC numbers.

The EMC number is usually a 4 digit numerical code, though in a few cases there are additional characters.

Model Identifiers often cover a narrow range of Macs. Usually one particular type of Mac, with a specific screen size, released at a particular time. Though in some cases a later revision that is substantially similar, will carry the same Model ID.

Staring with the Intel Macs released in 2006, Model IDs were in the format MacNameX,Y where MacName is a recognisable Mac model (iMac, MacBookPro etc.), and the X and Y are numbers.

However in 2022, a couple of years after the ARM switchover, Apple started using the format MacX,Y - the X and Y are numbers, but the "Mac" is the same across different models.

Old pre-Intel (PowerPC) Macs were almost all PowerMacX,Y or PowerBookX,Y (the exception being the very first iMac, which is: "iMac,1").

Model numbers, also sometimes called family numbers, are an identifier that often cover a fairly wide range of Macs. In cases where the fundamental design of a Mac has remained mostly unchanged, but incremental upgrades have been made to internal components, a single Model Number can cover more than 20 individual Macs, released over several years. Other Model Numbers are unique to a single machine.

It is usually a 5 character code in the format AXXXX, where the Xs are numerals. Some very old Macs have a Model Number that starts with an "M" rather than "A".