Siemens AG, which took 15 years to make up its mind to take the plunge and enter the UK computer market, is now getting serious about it, and, two years after its arrival here, has formed a separate Data Systems group to market its 7.000 series mainframes, departmental Unix computers, and, for the first time, the Fujitsu Ltd VP line of IBM-compatible scientific supercomputers, which it markets in Europe – in competition with Amdahl Corp.