IBM X23 - Manual (Page 60)

After you have replaced the system board, restore the
serial number by doing the following:
1. Install the ThinkPad Hardware Maintenance Diskette
Version 1.60 and restart the computer.
2. From the main menu, select 1. Set System
Identification.
3. Select 1. Add S/N data from EEPROM.
Follow the instructions on the screen.
Note: The serial number of the system unit is written
on the label attached on the bottom of the
computer.
Retaining the UUID
The Universally Unique Identifier (UUID) is a 128-bit
number uniquely assigned to your computer at production
and stored in the EEPROM of your system board. The
algorithm that generates the unique number is designed to
provide unique IDs until the year A.D. 3400. No two
computers in the world have the same number.
When you replace the system board, you must set the
UUID on the new system board as follows:
1. Install the ThinkPad Hardware Maintenance Diskette
Version 1.60, and restart the computer.
2. Select 4. Assign UUID from the main menu. A new
UUID is created and written. If a valid UUID already
exists, it is not overwritten.
56 ThinkPad X20, X21, X22, X23, X24