They are made up of data. Occasionally, they would strive to purchase skins - human, demons, animals, plants, etc. - to make themselves presentable or just due to mere curiosity.
Although they have extremely slow emotional development, it still exists. In long torrents of time, many of them have fallen in love with their tasker, made friends or family with the tasker, or want to stay with some other system. A great example is the main system itself. Wearing a western elf skin and accompanying system 001, who likes wearing eastern fantasy skins, all the time.
Some systems were turned from taskers after they died during tasks and agreed to become systems. The taskers were supposed to complete their tasks without dying, before the tasks are completed, with the prize being the points and their second chance at life. If they die, for the third chance of living along with their own memories and not being reincarnated as a new person, there's obviously much more to pay.
A system however can't go for tasks by itself and needs a tasker. So, many of them go regularly to all kinds of worlds to find a tasker for themselves. When they register a tasker, they get back soul power bonuses too.
All systems got a personal inventory that can be used any time without spending points by the tasker, but the upgrade needs lots of soul power.