Rather than risk the things ending up in hostile hands, Silicon Graphics Inc, Mountain View, California has decided to buy back most of its shares held by Control Data Corp. It will buy 2.36m shares at $22.60 a share and will fund the $53.3m repurchase price with $36.3m cash and a short term note to Control Data for $17m. Aft er the buyback, Control Data will hold 702,750 Silicon Graphics shares representing just under 5% of the total outstanding, and James Ousley, president of Control Data’s Computer Products Group, will resign from its board. CDC will continue to be an important OEM customer for the comp any’s Iris 4D graphics workstations.