ISO 9001 is about quality management for businesses in general. It sets out principles for quality management. On the other hand, ISO 9126 establishes standards to determine software quality. According to the latter, software quality evaluation should ensure that a software has the following properties; functionality, reliability, usability, maintainability, efficiency and portability. You can read more about that at http://www.angelfire.com/nt2/softwarequality/ISO9126.pdf