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Retaining serial numbers
This section includes the following descriptions:
• “Restoring the serial number of the system unit” on page 56
• “Retaining the UUID” on page 56
• “Reading or writing the ECA information” on page 57
Restoring the serial number of the system unit
When the computer was manufactured, the EEPROM on the system board was loaded with the serial
numbers of the system and all major components. These numbers need to remain the same throughout
the life of the computer.
If you replace the system board, you must restore the serial number of the system unit to its original value.
Before replacing the system board, save the original serial number by doing the following:
1. Install the LENOVO ThinkPad Hardware Maintenance Diskette Version 1.76 or later, and restart the
computer.
2. From the main menu, select 1. Set System Identication.
3. Select 2. Read S/N data from EEPROM.
The serial number of each device in your computer is displayed; the serial number of the system unit is
listed as follows:
• 20: Serial number
Write down that number.
Note: The serial number of the system unit is also written on the label attached to the bottom of the computer.
After you have replaced the system board, restore the serial number by doing the following:
1. Install the LENOVO ThinkPad Hardware Maintenance Diskette Version 1.76 or later and restart the
computer.
2. From the main menu, select 1. Set System Identication.
3. Select 1. Add S/N data from EEPROM. Follow the instructions on the screen.
If the MTM and Product ID numbers differ from each other on the rear label, use what is shown for the
Product ID eld. See example below:
MTM on rear label:
TTTT-CTO S/N SSSSSSS
Product ID on rear label:
TTTT-MMM (Use this number when setting Serial Number)
In the example, the Serial Number to be input is '1STTTTMMMSSSSSSS'.
Retaining the UUID
The Universally Unique Identier (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 number is designed to provide unique IDs until the year A.D. 3400. No two
computers in the world have the same number.
56 ThinkPad T520, T520i, and W520 Hardware Maintenance Manual