The ornamental design for a computermainframe, as shown and described.
The file of this patent contains at least one drawing/photograph executed in color. Copies of this patent with color drawing(s)/photograph(s) will be provided by the Office upon request and payment of the necessary fee.
1.1 is a front view of a computer mainframe showing the new design;
1.2 is a back view thereof;
1.3 is a left view thereof;
1.4 is a right view thereof;
1.5 is a top view thereof;
1.6 is a bottom view thereof; and
1.7 is a perspective view thereof.
The portions of the computer mainframe shaded red and surrounded by broken lines form no part of the claimed design.