Control Data Corp is finally severing all connections with its Comm-ercial Credit financial services unit, 20 years after it acquired the company. It floated Commercial Credit off late last year, and now plans to sell back to Commercial Credit the 18.3% minority it ret-ained, at $33 a share, which will bring CDC a total of $313.5m, on which it will have to pay capital gains tax because the shares are on its books at $18.50. The staged sale between now and the end of the year will lead to extraordinary gains for CDC’s third and fourth quarters, and CDC is considering using most of the cash to redeem its $227.3m issue of 12.75% senior notes offered last year with a mat-urity date of 1991. The $100 face amount stock is trading at $103.5.