Model M Keyboards are known for their loud clacking keys, tactile feedback and solid construction. The earliest models were built in the 1980s, so it follows that they wouldn’t be as efficient as modern keyboards when it comes to power consumption. Some websites indicate modern keyboards use just a hundredth of the power that a Model M does, which is a significant claim. But is it true? I decided to find out for myself.
What is the source of this claim?
The source of this claim appears to be an old Geocities web page created by John Szybowski. In the linked article, he write:
The IBM draws around 112mA from the interface, whilst a modern keyboard draws 1.2mA. These figures are with the 3 status LEDs (NumLock, CapsLock, ScrollLock) off. Each of these draw around 12mA when lit on both keyboards.
The article is well written, but it doesn’t provide details of how he obtained these measurements. For the sake of providing some hard data, I decided to measure the current draw on several Model M keyboards and several “modern” keyboards.
Model M Power Consumption
| Make | P/N | Date Manufactured | Current in mA, LEDs off | Current in mA, LEDs on |
|---|---|---|---|---|
| IBM (Lexmark) | 82G2383 | 09/13/1995 | 97 | 126 |
| IBM (Lexmark) | 82G2383 | 09/29/1994 | 101 | 129 |
| Unicomp | 2001 | 7 | 29 | |
| IBM | 1395240 | 12/07/1989 | 103 | 120 |
I’m seeing values around 100mA, so it seems the 112mA John measured is reasonable. It’s interesting to note that the more modern Unicomp Model M draws significantly less current. This is likely due to a more efficient circuit being used in modern Model M keyboards.
(Note: I don’t have a P/N and complete date for the Unicomp because it’s installed in an old Lexmark IBM case.)
Modern Keyboard Power Consumption
Here are the results of the “modern” keyboards I tested. For the purposes of this test, I considered any keyboard with Windows Keys to be modern, as those were first introduced in 1995.
| Interface | Make | Model | P/N | Current in mA, LEDs off | Current in mA, LEDs on |
|---|---|---|---|---|---|
| PS/2 | Dell | RT7D00 | 025PGG | 3 | 39 |
| PS/2 | Logitech | Y-SAF76 | 867633-0403 | 3 | 35 |
| PS/2 | HP | 5107 | 5187-3549 | 3 | 39 |
| USB | Logitech | Y-U0009 | 820-004520 | 4 | 33 |
| USB | Dell | SK-8115 | 3 | 51 | |
| USB | Dell | KB4021 | 0DJ454 | 4 | 16 |
| USB | Microsoft | 1366 | X818767-001 | 3 | 48 |
This is a small sample, but all of these are fairly typical keyboards from well known companies. I’ve rounded the numbers, but even before rounding the lowest value I saw was 2.6mA.
Conclusion
I didn’t find a keyboard that draws 1.2mA, but 2.6mA is still impressive and much more efficient than any of the Model M keyboards, including the newer Unicomp model. Based on my findings, modern keyboards are approximately 25-40x more efficient than Model M keyboards, not 100x.
Testing Notes
All keyboards were tested while connected to a Dell Optiplex 990 personal computer. Every keyboards was verified to be in working order while under test. An Amprobe AM-570 Digital Multimeter (DMM) was used for measuring current.
The PS/2 keyboards were interfaced to the computer using an IOGEAR GUC100KM USB to PS/2 adapter and a PS/2 extension cord on which I cut the VCC line to place the DMM inline for current measurement.
For the USB keyboards, I used a Fried Circuits USB Tester to connect the DMM inline for current measurement.
This article is a rewrite of one I originally posted on an old website on March 23, 2017.