Can someone explain the xx20 series keyboard?

[Thinkpad4by3]

The T6x keyboard has a small escape and small delete, which makes the top row have 15 keys from left to right.

The xx20 is the exact same width but there are 16 keys from left to right.

What was shortened to make this fit or is this a TARDIS where it's bigger on the inside?

[TPFanatic]

The bar with the dedicated buttons Mute,Volume,Think,Power was shortened a little and moved left, they moved the Insert key left to create an 8-key cluster starting with F9, and the gaps between the Fn-key clusters were shortened too.

See these images of comparison:
T410
T61

It's a great keyboard but I prefer the T61 keyboard especially in a nice big laptop like R500 or T500.

[CASPER]

Are keyboards from series xx00 and xx20 interchangeable ?

[Thinkpad4by3]

Only the T400s. The X200 & X300 uses its own special keyboard. The T400/T500/R500/W500/W700 use the T6x keyboard.

On the contrary, all xx10 series machines use the xx20 keyboard but xx01 machines don't like X301, W701, X201.

[TonyJZX]

always use the matched or equiv. SKU to be sure

IMO the final 410/420 edition kbd is the best ever however the 400 series is also pretty darn good since it has to roots in the T61 which is going way back

the 61-400 board is over 5yrs in production/use etc.?