A bit of background information:

The Casio sk-5 sampling keyboard was the successor to the earlier sk-1. I'm not entirely sure precisely which year they were introduced, sometime around 1986-88 seems probable. The sk-5 has the following features:

A 32-note minisize keyboard

Eight preset tones ten preset rhythms with variable tempo

Four preset percussion samples triggered by rubber pads

The ability to capture and store up to four samples and replay them using a further four rubber pads or the keys.

Samples can also be tuned and manipulated using six preset envelopes and reverse and loop functions

A three-part onboard sequencer with variable tempo

The ability to store sample and sequence data if 5xAA batteries are used

A built-in condenser microphone for sampling

Mic and line level inputs for sampling

A headphone / line output

Other SK-series keyboards included:

The SK-1
(more basic, fewer samples but included a slightly-programable synthesiser)

The SK-2
(very basic, almost no features)

The SK-8
(read song data from ROM cartridges)

The SK-8a
(as SK-8 but with the option of using Arabic scales)

The SK-10
(similar to SK-1 but more basic)

The SK-100
(larger keyboard, stores four samples but lacks the trigger-pads of the SK-5, preset sounds are very bland and cheap-sounding)

The SK-200
(as SK-100 but with stereo speakers / outputs)

The SK-2100
(as SK-200 but with full-size keys)

None of the above are as good as the SK-5