of GRAPE-4 is effectively 50 times faster than a Cray YMP.

At present, a 32k-particle system is about the largest system we can try for equal-mass case. Since the calculation speed of GRAPE-4 is still limited by the speed of the host computer, the actual calculation speed is roughly proportional to $N$ for $ N< 2\times
10^5$. Thus, the CPU time for globular cluster simulation on GRAPE-4 is proportional to $N^{2.3}$. A 64k-particle run would take about one year.

The above estimate is for an equal-mass isolated cluster of point-mass particles. The computational cost of more realistic calculations depends on many factors. Among them, the mass spectrum and the presence of primordial binaries are most important, and have adverse effects.

Systems with a mass spectrum evolves faster than equal-mass systems (see, $e.g.$, [@Inagaki1984], [@Murphy1988]). Therefore it is possible to handle a larger system. For example, if the evolution of the system is $p$ times faster, GRAPE-4 can handle the number of particles $\sqrt{p}$ times larger. Thus, if the collapse is 4 times faster, GRAPE-4 can finish a 32k-particle run in 3 weeks or 64k-particle run in 3 months.

The presence of the primordial binaries would increase the CPU time. At 