Thanks for the questions.
First, a little clarification. The FPO (a.k.a. batch) number is printed on the metal heat spreader on our desktop processors (it may be in a different place on mobile processors). It is only 8 characters and does not include any ‘serialization code’.
We do sometimes print a serial number on our CPU’s (usually on a black strip, next to a ‘2D matrix’ barcode, but it is not present on all processor models. You can’t count on it being there.
Now to your question. The 5th digit of the FPO number is unrelated to the core stepping of the CPU. It is simply part of the 4 digit batch numbers for that work week.
I need some clarification on what you mean by the 5th digit of the FPO is unrelated to the Stepping core, but that it is part of the 4 digit batch number of that work week. If that is so then the following FPO on I/O Controller Hub 5 (L3110081) reads like the following.
1st letter or digit = plant code (Malay)
0 = San Jose, Costa Rica
1 = Cavite, Philippines
3 = .............., Costa Rica
6 = Chandler, Arizona
7 = .........., Philippines
8 = Leixlip, Ireland
9 = Penang, Malaysia
L = ............, Malaysia
Q = ..........., Malaysia
R = Manila, Philippines
Y = Leixlip, Ireland
2nd digit = Year of production (2003)
3rd -5th the work week. Week 110.
6th - 8th serial code.
I ask since we do not have 110 weeks in a year.
Please let me know if that is how to interpret the 5th digit?
The first character (number or letter) belongs to the manufacturing country.
The second number is the manufacturing year.
The third and fourth numbers are the work week.
The rest of the characters are for internal use