  Exa-scale simulations are on the horizon but almost no new design for the
output has been proposed in recent years. In simulations using individual time
steps, the traditional snapshots are over resolving particles/cells with large
time steps and are under resolving the particles/cells with short time steps.
Therefore, they are unable to follow fast events and use efficiently the
storage space. The Continuous Simulation Data Stream (CSDS) is designed to
decrease this space while providing an accurate state of the simulation at any
time. It takes advantage of the individual time step to ensure the same
relative accuracy for all the particles. The outputs consist of a single file
representing the full evolution of the simulation. Within this file, the
particles are written independently and at their own frequency. Through the
interpolation of the records, the state of the simulation can be recovered at
any point in time. In this paper, we show that the CSDS can reduce the storage
space by 2.76x for the same accuracy than snapshots or increase the accuracy by
67.8x for the same storage space whilst retaining an acceptable reading speed
for analysis. By using interpolation between records, the CSDS provides the
state of the simulation, with a high accuracy, at any time. This should largely
improve the analysis of fast events such as supernovae and simplify the
construction of light-cone outputs.
