If you can manage it, one of the best tricks to pull at a major exhibition is to announce a major new product halfway through the show so that it doesn't get lost in the flood of first day announcements and gives the attendant scribes something big to write about during the later days - and DEC pulled the trick superbly at UniForum in San Francisco. On Wednesday night, London time, the company pulled the wraps off a multi-user version of its MIPS Computer Systems Inc RISC-based Ultrix line, in the process reviving the hallowed DECsystem name, dubbing the box the DECsystem-3100. Based on the 16.7MHz R2000 version of the MIPS RISC with R2010 maths co-processor, the machine comes with Ultrix licence, X Window, DECwindows, TCP/IP commu nications and optimising C compil er, and is rated by DEC at 14 MIPS, 3.7 MFLOPS on the single precision Linpak benchmark. DEC is pitching the machine at the commercial mult i-user, laboratory data reduction, and engineering simulation and ana lysis markets, and is touting the launch as a price breakthrough in multi-user Unix machines. It costs $20,400 with 8Mb, three 332Mb disks and support for four users, $22,004 with 8Mb, one 332Mb disk and supp ort for eight users, and $55,604 for a 32-user system with 24Mb and three 332Mb disk drives. It is ta king orders now for ships in June.