兼容分时系统（英语：Compatible Time-Sharing System，缩写为 CTSS），最早的分时操作系统，由美国麻省理工学院计算机中心设计与实作，计划领导者为费南多·柯巴托。1961年首次进行示范运作，1962年发表论文，一直运作到1963年为止。麻省理工学院的MAC计划拥有它的第二份拷贝，它只在这两个地方运作过。

在兼容分时系统的基础上，发展出接下来的Multics操作系统。

The Compatible Time-Sharing System (CTSS), was one of the first time-sharing operating systems; it was developed at MIT's Computation Center. CTSS was first demonstrated in 1961, and was operated at MIT until 1973. During part of this time, MIT's influential Project MAC also ran CTSS, but the system did not spread beyond these two sites.