Music sequencing originated in the late 80's. It began with the release of so-called music trackers, programs that allow users to arrange synthesized notes on a timeline over several monophonic channels. The first tracker to become available to the public as a commercial product, came with the release of Ultimate Soundtracker for the Amiga. Popularity of trackers in general however rose, when programmers began to release freeware clones of this program. The most infamous clone was FastTracker 2. The trackers soon featured sample playback instead of synthesized notes. The music made with synthesized audio trackers became popular due to its use in early videogames and its use in the demoscene. Synthesized tracker music became know as 'chip music'.
The earlier version of the music trackers allowed samples to be played over 4 mono channels at one time. With better hardware being developed it soon evolved into 8, 16, 32 and 64 channels of audio. Trackers have a distinctive vertical timeline on which the notes or samples are placed. Nowadays Renoise is probably the only real tracker software that is still actively supported.
So, what is music sequencing? As the name sequencer suggests, you can put sounds in order on a timeline to be played back. The old 'trackers' from the early days were all essentially music sequencers.
When MIDI became the standard to control music sequencing, the trackers evolved into digital audio workstations. Programs like Steinberg's Cubase and Propellerhead Reason became virtual home studios, which could play back samples and synthesized sounds, record, edit and play back digital audio tracks.
By using samples of live recorded instruments, the newest generation of music sequencers enable users to use a midi device (like a keyboard) to generate those recorded sounds in a very convincing way. Evenif you can't really play the guitar or play the drums, you can magically turn your keyboard into any instrument conceivable and have a blast fooling around. You might just end up making that cool song you dreamt about, because all the instruments known to man await you.
Below you can play one of my very first tracks made with music sequencing, using good old Fast Tracker 2. It's made somewhere in the late 90's. Try not to laugh :)
After listening to that track, see if technology has advanced when you compare the above song to my later ones, made with the latest technology. Just think of the possibilities if you bare in mind that all those songs were made, just using a modern music sequencer and a MIDI keyboard.