A computer system with vertically offset hard disk drives has a space in one side for containing the two vertically offset hard disk drives held by a mobile rack in a vertically offset manner. The mobile rack fixes the two hard disk drives with two vertically offset screw sets. A holding frame in the space of the computer system has two vertically offset connectors that allow the two hard disk drives to be connected at the same time when the mobile rack is completely inserted into the holding frame.