I think a lot of it is Helvetica.

I think sans actually makes sense because it's simpler and unobtrusive. Plus sans forms are closer to what we make when we write (not too relevant these days though) and they're easier to decipher individually.

As for them being white-on-black: note that a lot of laptops have lighted keys...

BTW it's very interesting that most keyboards use oblique type. I couldn't figure it out until I used a late-model Mac (which uses upright type) to type something: the letters on the left looked like they're falling backwards, and there's an overall impression of inconsistency - quite disconcerting.

hhp

> As for them being white-on-black: note that a lot of laptops have lighted keys...

Yes I think that's a factor. And on laptops, which are frequently a silver color, the contrast of darker keys looks nice. Another factor might be that Apple switched to black keys on their MacBook Air and Macbook Pro a few years ago, and since those models have sold very well the look may have influenced some other laptop makers.

@hrant:
I think a lot of it is Helvetica.

Indeed, because that's what IBM used on the original keyboard for the IBM Personal Computer.

Other keyboard makers today will imitate the Macintosh, and use an italic sans-serif typeface.

Before the IBM PC, while there were exceptions, the standard for keyboard keycaps was Leroy lettering. For those who are unfamiliar with this, it's a type of lettering guide so that a drawing pen will move in the shape of a letter, made by Keufel and Esser.

If I remember correctly, the IBM Selectric typewriter I used in the late 1970s had black keys with white sans-serif letters (not sure if it was Helvetica or not).

In fact if you Google "typewriter keyboard" you'll see numerous examples of old typewriters that are similar in keyboard style (although the keys were often round).

I refer to the wordy keycaps, for example, "Print Screen SysRq", PgUp, PgDn, Del, Caps Lock, Shift, Ctrl, Alt Gr, Tab, Insert, Delete, Home, End, F1....F12, etc and the keycaps' small areas at least on some keyboards in the UK.

Could some keyboards font typeface/s also have gone through on these wordy keycaps and/or keycaps' word/s individual letter/s, with or without sectioning to keyboard area/s, by this process:

(1) spaces between each letter in a word condensed manually (standard / different) to ensure it was between the horizontal up and down margin and the vertical left and right margins, with or without sectioned to keyboard area/s?

and/or

(2) used more than one font on the keyboard where one keycap has one font and another keycap another font depending on where the condensing is needed, with or without sectioned to keyboard area/s?

and/or

(3) used different font sizes standardized across the keyboard depending on where it is needed, with or without sectioned to keyboard area/s?

and/or

(4) used another font size on a certain keycap word/s letter/s and some other size on another letter/s on the same, with or without sectioned to keyboard area/s?

and/or

(5) used mixed fonts in an individual keycap depending on where it is needed, with or without sectioned to keyboard area/s?

or

(6) are the above views not applicable and instead the variations noticed are caused instead individually or in combination by all or part, the concave keycaps, the positioning of the keycap word on the concave, the keycap size and thus also the concave, thin or wide letters in a keycap word, plastic texture, keyboard build process, keycap ink and equipment etc?

For a while Apple used Univers italic. Now I think it's VAG Rounded.

There are other fonts suitable for keyboards. I would be interested to find out what is your favourite from the below that seem not to have wide glyphs seen in part on a font comparison internet site and another part on a different internet site thereby providing more flexibility on the keycaps:

Nimbus Sans L
Swansea
Liberation Sans
Bitstream Vera
IndUni (only english language keyboard sort font)
Actor
Cabin
Oxygen
PT Sans

Suddenly I realize what the font must be: Courier!

hhp

There is a font that resembles Leroy lettering closely: Sublime
and here's a description of the system.

And then there's Simpliciter Sans and even Squa Tront! .