As I recall it was discovery in the Comes case vs MS that proved it. They'd had meetings to brainstorm ways to make competing software have continuous 'difficulties'. Through the 80s MS hadn't updated their operating system. Dos 3.3 needed all sort of helper software to be able to function with a network, mouse or any other driver. You'd use up the 640k of low memory and your application or game couldn't run. You needed a memory manager at least to be able to use the 640k-1024k area for the device drivers and to provide a memory interface to higher memory addresses. MS Dos 4 failed completely (early Vista?).
Digital equipment stepped in and made an advanced Dos that MS never reached feature parity with even with MS Dos 6 ( Dr. Dos ). Demand for storage had skyrocketed but hard drive pricing was stagnant. Processors had improved, so Stack made an innovative transparent hard drive compression system that loaded like a SCSI drive. Awesome stuff. So, MS created software that reported fake error messages if you used Dr. Dos and release MS Dos 6 with drive compression allegedly stolen from Stack. MS stalled the lawsuit from Stack until they ran out of money and folded. They tried that with Dr. Dos, but a lawfirm deep pockets managed to buy Dr. Dos and pursue the case. MS had been putting information about anti-competitive unlawful behavior in writing, which came out in that case. MS was behaving that way. It looks like MS sought single product profitable companies without a big cash reserve that couldn't complete a lawsuit if MS cut off their sales. Then take the product in some way, alter the OS to keep crashing with the victim product and use leverage with the sales channels to cut off opportunities to make sales. (later example - MS threatens to withhold Windows licenses from Compaq during Christmas if Compaq doesn't remove Quicken and replace it with MS Money on all PCs)