IBM Corp has begun the dismantling of its Desktop Software unit, and it looks as if XyQuest Inc, Billerica, Massachusetts is pretty much on its own with the Signature word processor it developed at IBM’s request. IBM assigned marketing and distribution rights to the product back to XyQuest, and IBM will simply offer it in the US on a co-operative marketing basis. Also going back where they came from are the marketing and distribution rights to the Platinum Series of accounting programs, which runs under both OS/2 and MS-DOS were developed by Advanced Business Microsystems Inc, Irvine, California. IBM dealers will market the IBM logo version until January 1992, when Advanced will start marketing the product.