Prior to computer memory-based samplers, musicians used tape replay keyboards, which store recordings on analog tape. When a key is pressed the tape head contacts the tape and plays a sound. The Mellotron was the most notable model, used by a number of groups in the late 1960s and the 1970s, but such systems were expensive and heavy due to the multiple tape mechanisms involved, and the range of the instrument was limited to three octaves at the most. To change sounds a new set of tapes had to be installed in the instrument. The emergence of the digital sampler made sampling far more practical.
The first digital sampler was the EMS Musys system, developed by Peter Grogono (software), David Cockerell (hardware and interfacing) and Peter Zinovieff (system design and operation) at their London (Putney) Studio c. 1969. The system ran on two mini-computers, Digital Equipment’s PDP-8s. These had 12,000 (12k) bytes of read-only memory, backed up by a hard drive of 32k and by tape storage (DecTape). EMS equipment was used to control the world’s first digital studio.
When you assign samples to a keyboard they can be played like a piano. You can record the MIDI data from your keyboard or controller and trigger these samples on playback. The all important feature is that you can assign a sound to any key(s) at any pitch you want. A decent soft sampler lets you layer sounds, stacked on top of each other like a layer cake. You can map the keyboard to emulate traditional instruments, drum kits, or you can place a whole bunch of loops and beats on the keys. I often build new keymaps for each song and build a completely fresh sound out of all the samples I have that fits the song rather than hunt for a preset that will work.