Few MIDI keyboards have a layout as indicated above with the full 128 keys (rem. that "0" is a number as well) but while many may be termed as full sized keyboards or having 49, 60 etc. keys,  most have "up"/"down" buttons which raise or lower the keyboard pitch by 1 or 2 octaves thereby giving access to the full 128 keys .

For MIDI convenience each key on the MIDI keyboard is allocated a number from 0 - 127 as on the top keyboard and sometimes from 1 - 128. For further identification and simplification they are also divided into octaves as above but from C1 - C12. Middle C for example is key no. 60 and also C5.The notes D and E immediately above middle C, for example, would be notes 62 and 64 (C sharp and D sharp would be 61 and 63).They could also be called D5 and E5.

                                                                                                                                                                                                        (Picture courtesy of Roland)
The PC-160 above is a "controller" keyboard. It actually controls the sounds and other parameters (volume, reverb, pan, patch change etc.) from the sound source it is using. It produces no sounds of it's own and therefore must be connected via a MIDI cable  to an external sound source such as another music keyboard, a computer sound card, an external sound module etc.