What Is Old IMEI Number: TAC and FAC Terms

What is IMEI number that is given to every mobile device in the world? Each IMEI is usually present in the form of 15-digit or 17-digit number. Our modern mobile world is using the following format customers are used to: AB-CDEFGH-IJKLMN-Z. What do the parts of this format stand for and mean to users?

There are a lot of interesting details about IMEI number. For example, you can check if your iPhone is stolen using its IMEI number. But let’s start from the very beginning and get into the terms related to this code.

What Is IMEI Number

About ME Type and GSM ME

Term ME is usually defining the mobile device that is identified with unique IMEI number. ME stands for Mobile Equipment and it is describing the GSM gadgets that are available in the market. This sounds pretty simple, isn’t it?

There are many hardware platforms on which GSM Mobile Equipment models are based. They are manufactured by different companies and have different ME Type. You can guess that ME Type models can get changes in hardware design, enhancements and other things manufacturing process add to devices. The companies are using ME Build Level and give their products different build numbers to reflect the changes.

Devices are allocated an IMEI – this process is known as Type Allocation. The GSM Association appoints organizations [they are referred to as Reporting Body] that have the authority to allocate IMEI numbers to different ME Types [you can find out if your iPhone IMEI is valid or not]. This happens in every country and there might be several Reporting Bodies in the same area. These Reporting Bodies not only have the right to allocates IMEIs but can also permit the use of device on your network using its IMEI code.

We know that this could sound complicated but these are details about IMEI number that can help you understand this term and its nature. So let’s put everything in simple words: ME is the device that has the IMEI code which was allocated by Type Allocation Holder which is not always your original ME manufacturer.

ME Type IMEI devices


Now as we got acquainted with main terms associated with IMEIs – let’s get back to the number structure and take a closer look at AB-CDEFGH-IJKLMN-Z format familiar to millions of iPhone and other mobile device owners.

The historical IMEI structure contained TAC, FAC, Serial number and Check digit. Such structure was valid till December 31st, 2002. TAC used to be Type Approval Code and is now the Type Allocation Code. FAC was the Final Assembly Code. If we return to our main formula, we’ll see that:

* AB standed for TAC code [or Reporting Body Identifier]

* CDEFGH standed for the remainder of TAC [FAC]: CDEF referred to ME Type Identifier and GH could indicate the manufacturer and was under control of the Reporting Body

* IJKLMN was the serial No [it was Allocated by Reporting Body however only manufacturers could assign it to ME models]

* Z was the check digit [it defines as a function for all IMEI codes]

Then the industry decided to change this IMEI structure and TAC + FAC were combined into the single 8-digit TAC code [the FAC had to be considered as obsolete]. It is understood that such changes couldn’t happen within one or two days. There was a 2-year transition period between December 31st, 2002 and April 1st, 2004.

Old IMEI Structure Before 2002

The TAC codes that were allocated for the two ‘transition’ years included the first 6-digit just as they should and the 2-digits (seventh and eighth ones) were 00. This helped companies to modify their productions, operators to add changes to their systems and start using 8-digit TAC codes instead of the 6-digit codes. At the same time, Reporting Bodies were able to apply changes to IMEI allocation systems and the GSM Association could update its databases.

Whenever a new FAC code was requested by manufacturers between 2002 and 2004 – they were provided with a new 8-digit TAC code instead. Thanks to such a procedure, the industry was able to start using the new codes and din’t have to change the whole IMEI analysis. The tracking systems weren’t affected by the changes as well.

The modern IMEI numbers don’t have the FAC code any more. They all have the 8-digit TAC number + Serial number + check digit and you are welcome to learn more about the new IMEI structure you might have on your mobile device.