The "Blue Switch" - 1984 IBM 3178-C3 Model F Terminal Keyboard

1984-made IBM 3178 Model C3 Display Station Typewriter Base Keyboard (P/N 6052101)

Quick summary:

  • 31XX-87 type Model F Base Keyboard
  • 87-key US English EBCDIC layout
  • IBM buckling spring clicky key-switches
  • Dye-sublimated PBT keycaps
  • Made by IBM United States
  • Also known as a “blue switch” Model F due to its characteristic switch originally used for toggling the host terminal’s text display between mixed-case and upper-case only.
  • The keyboard has a solenoid inside used to increase key-stroke volume.
  • A storage compartment is present on the bottom for a guide for the host terminal.

I recently got this C3 and whilst I originally was going to just post in the “Post Your Keyboards” thread, I’ve been writing a lot about them so…

Better known as [one of] the “blue switch” Model Fs due to its characteristic toggle switch, this was a terminal keyboard introduced in 1983 for the eponymous IBM 3178 Model C3 Display Station. The overall design is from slightly earlier though, since there were four total variants, the first two of which were introduced in late 1982:

  • IBM 3104-B1/3178-C1 75-key Data Entry Base Keyboard
  • IBM 3104-B2/3178-C2 87-key Typewriter Base Keyboard
  • IBM 3178-C3 87-key EBCDIC Typewriter Base Keyboard
  • IBM 3178-C4 87-key EBCDIC Typewriter Base Keyboard

Simple comparison (note the keypad and what’s on it):

B2/C2 through C4 are what I call a 31XX-87 type Model F due to the fact some of them were used across different terminals - 31XX terminal family (the 3104 in addition to 3178), 87 keys, Model F keyboard family. The B1/C1 model is the 31XX-75 type Model F that lacks the right-most keypad. There was also another terminal keyboard based on the same platform but without the blue switch for IBM 3101 and 7485 Display Terminals which additionally had a panel of DIP switches underneath a cover on its ‘forehead’.

The IBM 3104 Display Terminal and 3178 Display Station were both IBM 3270 family terminals initially released in December 1982 and March 1983 respectively. They differed in how they ultimately connected to a host processor (3270 itself is intended for IBM mainframe usage), but they were both capable of providing similar levels of functionality to that of the earlier IBM 3278 Model 2 Display Station but at a lower cost.

As I recently discovered, the IBM 3104/3178 keyboard family were officially considered by IBM to be a part of the IBM Base Keyboard family. This was a physical layout lineage that originated in 1977 with IBM 3270 terminal family Model B keyboards.


So if anything, keyboard foreheads are actually smaller today.