Some Apple keyboards, such as the Apple //e, some early Macintosh models, and the venerable Apple Extended Keyboard have the homing bumps on the D and K keys instead of the standard F and J keys that almost everyone else uses. (e.g. IBM's venerable Model M)
Why? It frustrates touch typists so it seems like there must be some good reason.
The official answer (archived here) is that they pretty much made it up as they went along:
At some time in Apple's history it was decided to put the "bumps" on the D and K keys while some other computer companies use the F and J keys. With the release of the PowerBook G3 Series, Apple moved the bumps to the F and J keys.
Apple engineering has indicated there is no standard, such as ISO or ANSI that specifies which keys should have these "bumps," or that they should have the "bumps" at all.
Personally I know this from a typewriter course in school (ca. 1973). The machines we used hat slightly different cavity on D/K to support touch-typing. we were supposed always rest our middle fingers there while having the rest afloat. A similar lesson was given for the use of adding machines with a similar keycap for the 5 key. But so far I couldn't find any reference online.
This was Germany. Comments and other answer suggest that it was similar in other European countries (Denmark, Norway, Sweden). So D/K might have been a de facto standard for pre-computer typing to support a touch type method used at least in Europe, which Apple may have used.
Some Apple specific timeline:
Original Apple II, II+, III, Lisa and Macintosh didn't have any markings.
The IIe keyboard (1983) was the first to introduce them on D/K.
All later Apple II (IIe, IIc, IIc+) also got them while the 'professional (III, Lisa, Macintosh) stayed without.
The Macintosh Plus (1986) keyboard was the first in the Mac line with bumps (D/K).
They stayed there on all following (ADB) keyboards (Mac as well as Apple IIgs).
With introduction of USB keyboards(*1) with the eMac, they got moved to F/J.
All Apple Keyboards since ~2000 have them at F/J
*1 - Essentially using the PC keyboard hardware.
The bumps were on the D and K keys because these letters are touched by the longest fingers, which come into contact with the keyboard first if the hands are relaxed.
Landing on the wrong key is recognised instantly.
Having to bend your three fingers on each hand, lifting up the thumbs to make room for letting the index fingers detect being in the right position takes more effort. Also leaning on the keyboard idling is keeping into contact with the middle fingers on the D and K keys, confirming correct placements while hand muscles are relaxed.
This may not be a big effort, but if it is one you have to sustain all day, it matters. Back in the day it was rumoured that Apple had its word processors tested by typists that were used to mechanical type writers. I can imagine they also had a voice in the decision of bumping the D and K.
I learned to touch type while doing my service in the Swedish Air Force. We were trained to use D and K as home keys for left and right middle finger.
This was in 1989, and it was a standard in Sweden in touch typing courses.
I checked on two keyboards (all swedish variant): my LK201 keyboard: no marking on dfjk while the ibm type M at f and j.
Runes datormuseum has a picture of a ABC99 keyboard which is a mid 80s swedish made computer keyboard for the ABC1600 unix machine, this kbd has a small marking on F & J, so i wonder if it really was swedish made or if it was sourced from Japan for example.
