The time evolution of models for an isolated disk of highly flattened galaxies of stars is investigated by direct integration of the Newtonian equations of motion of N = 30, 000 identical stars over a time span of many galactic rotations. Certain astronomical implications of the simulations to actual disk-shaped (i.e. rapidly rotating) galaxies are explored as well.KEY WORDS Galaxies kinematics and dynamics galaxies structure-instabilities One can learn much about the properties of stellar systems of disk galaxies experimentally by computer simulation of many-body systems. We analyze the evolution and stability of structures in N -body models of isolated, rapidly and nonuniformly rotating, and spatially inhomogeneous stellar disks of galaxies by direct integration over a time span of Newtonian equations of motion of identical particles. Use of concurrent computers has enabled us to make long simulation runs using a sufficiently large number of particles. The essential difference between the present and previous simulations is the comparison between the results of N -body experiments and the stability theory as developed by Griv and Peter (1996), Griv et al. (1997Griv et al. ( , 1999aGriv et al. ( , 1999bGriv et al. ( , 2000 and Griv (1998).At the start of the N -body integration, our similation initilizes the particles on a set of concentric circular rings with a circular velocity V of galactic rotation in the equatorial plane; the system is isolated in vacuum. Then the position of each particle was slightly perturbed by applying a pseudorandom number generator. The Maxwellian-distributed random velocities v were added to the initial circular velocities V, and |v| |V|. Finally, slight corrections have been applied to the resultant velocities and coordinates of the model stars so as to ensure the equilibrium between the centrifugal and gravitational forces and to preserve the position of the disk center of gravity at the origin.In Figure 1 we show a series of face-on view snapshots from a three-dimensional simulation run of the so-called cold disk, in which the initial dispersion of random velocities of stars was chosen to be less than the critical Toomre's (1964) dispersion.