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[dellmodelm]

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[emmafrost1]

Yes, the letter at the beginning of an IBM Model M serial number does mean something special. The letter indicates the plant where the keyboard was manufactured.

A: Lexington, Kentucky
B: Chicopee, Massachusetts
C: Austin, Texas
D: South Carolina
E: Japan
F: Mexico
G: Taiwan
H: China
So, your keyboard with the serial number F4185 was manufactured in Mexico.

IBM changed the format of their serial numbers in the early 1990s, and the letter at the beginning of the serial number was no longer used to indicate the plant of manufacture.

[sharktastica]

Yes, the letter at the beginning of an IBM Model M serial number does mean something special. The letter indicates the plant where the keyboard was manufactured.

A: Lexington, Kentucky
B: Chicopee, Massachusetts
C: Austin, Texas
D: South Carolina
E: Japan
F: Mexico
G: Taiwan
H: China
So, your keyboard with the serial number F4185 was manufactured in Mexico.

IBM changed the format of their serial numbers in the early 1990s, and the letter at the beginning of the serial number was no longer used to indicate the plant of manufacture.

I would ask for a source for this but it seems this might be AI-generated...

But for the sake of the OP not being confused, regardless of origin, IMO the above doesn't seem to match up with current understanding of how IBM reported plant codes on keyboards. Being the nerd and the "shark with a massive database" that I am, I have records that seem to break the statements.

There are "F"-id Model Fs produced in 1984, which would be two years before the IBM Mexico Guadalajara plant would start making keyboards (I don't recall any other plant making keyboards before that). "H" has been spotted on an F122 and I have not heard of any IBM Model F or M being made in China, at least not until the 2000s when IBM used XSZ as the OEM for IBM Models M7 through M11 and those aren't even buckling spring. Some keyboards also have a number as the first digit instead.

Tangent time

To set the record on IBM plant/factory reporting, IMO, it's patchy at best. The obvious PLT "plant" numbers have been shared between keyboards obviously made in the US and the UK. When asked, IBM and Unicomp didn't recall what they meant and iirc ClickyKeyboards had a few theories that it might mean something completely different. The only plant code that makes sense to me is the two-digit integers Ardent Tool has listed since I can at least find them on keyboards. Here are some examples:

• 11 = Lexington: spotted on 3104/3178 IBM US Model Fs as the "plt", IBM US Model Fs and Ms with big barcodes on their rear label (for example, found in the H and F images above and OP's image).
• 55 = Greenock: spotted at the start of serial of most IBM UK Model Ms from before 1996.
• 58 = Amsterdam: spotted in the middle of serial of IBM NL Model M122s with the massive rear label.
• 78 = Guadalajara: spotted in the middle of serial and as the "planta" of IBM MX "Modelo" Ms. Eventually, was replaced with "IEP" for some reason.
• 91 = Canada (Bromont?): spotted at the start of serial of IBM CA Model B(eam spring)s and IBM 4680 POS Alphanumeric Keyboards (via the smaller sticker).

(If you're wondering why I went into detail, I'm working on an article on IBM plant codes and potential misconceptions with them hence why this is in my mind right now. Stay tuned, my friends!)

The return to OP's question

The short answer is that I don't think we know for sure what that letter means, but IMO it's likely just there to add another dimension to the ID/serial. 36 (26 letters plus 0 to 9). Without that digit, the possible ID/serial space would be very small indeed. IBM U.S. would have to made just 9,999 keyboards before requiring a change of ID/serial nomenclature. That said, there are other things strange about the serial space since as seen by this week 33 and 34 example of the same keyboard, the earlier keyboard has a higher number than the later! As I think I've said before, IBM just doesn't make sense and trying to make sense of it would be a full-time job.

[JP!]

[*] 55 = Greenock: spotted at the start of serial of most IBM UK Model Ms from before 1996.

Pulled from my database , an early production Model F AT. I was wondering what this particular ID meant. I didn't believe it to be the 55th unit produced.

AT.jpg (56.2 KiB) Viewed 2752 times

[Muirium]

I would ask for a source for this but it seems this might be AI-generated...

Yes, both the user’s posts look to be keyboard related AI. I say we ban them on the third. Should be along plenty soon.

“Group buys were invented in IBM’s West Germany research labs in Des Moines, Kansas.”

[sharktastica]

Pulled from my database , an early production Model F AT. I was wondering what this particular ID meant. I didn't believe it to be the 55th unit produced.
AT.jpg

Looks like the folks at Greenock forgot the rest of the ID! For reference, he's some completed Model F IBM U.K. birth certs:

F/XT:

3104/3178:

F122:

F/AT:


For anyone interested, I'm building up an archive of IBM and family rear labels on my site!

[JP!]

Looks like the folks at Greenock forgot the rest of the ID! For reference, he's some completed Model F IBM U.K. birth certs:

Indeed! Here is an example of my UK XT. Btw, both of my UK F's are the German variants.

XT.jpg (66.48 KiB) Viewed 2724 times

[emmafrost1]

[*] 55 = Greenock: spotted at the start of serial of most IBM UK Model Ms from before 1996,

Pulled from my database , an early production Model F AT. I was wondering what this particular ID meant. I didn't believe it to be the 55th unit produced.

AT.jpg

Ah this one is interesting.

[Muirium]

The spam you appended to it is most certainly not.