Abstract: A computer mainframe includes an open-topped case and a top cover provided with a handle to be easily pivotally lifted from an open top of the case. The top cover being pivotally turned to the lifted position enables convenient installation and replacement of peripherals, such as the hard disk, the CD-ROM, the interface card and the like, that are to be mounted in the case. A displaying screen may be mounted to an inner side of the top cover to enable easy movement of the whole computer mainframe to any place for use.