IN the past, Digital Equipment has been successful in pushing its proprietary VMS operating system. Today, however, the company is shouting about its support for open systems - particularly its non-proprietary Digital OSF/1 operating system. The company is banking on this open architecture and the power of its AXP series' 64-bit platform to keep existing customers and win over other brand users. ''DEC OSF/1 supports more standards than any other operating system,'' said Mr Stephen McIntosh, corporate marketing manager for Digital OSF/1. Mr McIntosh was in Hongkong last week to address Digital's seminar, Open Systems Open House. The Asian-region seminars coincide with Digital's release of volume shipments of DEC OSF/1, which it developed in two years and was based on the Open System Foundation's OSF/1 operating system. ''We call it the unified UNIX. It removes all the confusion about what kernel or version of UNIX has been used in an operating system and therefore removes doubt for both the software developer and end user,'' he said. While promoting DigitalOSF/1 as the UNIX system of the future, and the Alpha AXP series as the 64-bit architecture of the future, Digital is also offering its proprietary Open VMS and Microsoft's Windows NT. But Mr McIntosh denied Digital was covering too many bases by supporting two other operating systems. ''Those three operating systems are what our customers are demanding,'' Mr McIntosh said. ''Open systems means being vendor-independent, being able to interface any standard operating system. All three operating systems offered by Digital support the POSIX standard interface, and so give the freedom to choose between vendors, and within networks,'' Mr McIntosh said. The three operating systems Digital promotes will all support the important TCP/IP (Transmission Control Protocol/Internet Protocol) communications protocol and Digital's Pathworks Personal Computer (PC) integration package. Support for TCPIP allows file copying and restoration and mail functions between different operating systems. Pathworks, based on Netware by Novell, goes further to enable shared resources and data between different PC operating systems in a network. Running down the list of industry standards, DEC OSF/1 also supports the Open Systems Foundations (OSF) interface ''Motif'' which is also endorsed by COSE, the Common Open Systems Environment group. It also supports Distributed Computing Environment, another OSF-selected and specified applications-building software which is based on a number of companies' technologies. ''Digital OSF/1 supports 90 per cent of everything COSE is endorsing as a future direction, except HP Vue, a user interface based on Motif. ''And both Open VMS and Digital OSF/1 operating systems have the European standards group, X/Open's XPG4 standard approval,'' Mr McIntosh said. OSF's Tokyo-based regional managing director, Mr Jim Curtin, maintains that OSF/1 will quickly become more widespread by users as it is adopted by more vendors - and Digital certainly is not the only company to have committed to the platform. ''OSF/1 is shipping by name with Digital, but other companies like IBM, HP and Hitachi are also shipping OSF/1 compliant product,'' Mr Curtin said. ''There are a number of vendors that are shipping OSF/1, but who don't call it OSF/1.'' Mr Curtin also played down the significance of COSE, and said that it was so far looking only to standardising the UNIX desktop, but in the short term was not looking to address standardising the Unix kernel. ''So, aligning on the desktop is a minor issue, but it does bring together the two major camps - that is the USL/Sun group and the IBM/HP group to present a common front in the Unix market.'' The initial release of Open VMS is 32-bit, but is Alpha-based so users should find it easy to port applications and recompile when upgrading to the 64-bit Alpha-based version of Open VMS - when it becomes available. Digital and Microsoft have collaborated for a year since jointly announcing Microsoft's support for Digital's new, 64-bit Alpha chip. Digital is offering Windows NT because it is a key environment increasingly in demand and the important new processor and important new operating system would be more powerful together than separately. Windows NT's range of PC applications is not available on Open VMS or OSF/1 and, so the full range of Microsoft applications will be ported to the Alpha chip. Digital stakes its claim of offering vendor independence, and its slogan, ''unified Unix'', on the fact that DEC OSF/1 is a blend of today's two most-used UNIX operating systems, AT & T's original UNIX version 5, and Berkely Software Distribution's version, plus the Open System Foundation's operating system, OSF/1. In its two years' development on the OSF/1 system, Digital has added real-time capability according to the POSIX standard, and features such as logical volume managers to handle large files beyond the size of the disk - which is especially demanded by big commercial users who are now downsizing. In particular, Digital expects its operating systems will win new business from Sun PC and workstation users. Among those downsizing, Digital hopes to welcome converts such as Prime mini and mainframe users, and IBM mainframe users. Digital claims the Unix user market is already growing by more than one-fifth each year. ''In fact, anyone who is downsizing is looking to Unix as the standard because both Open VMS and DEC OSF/1 give the right combination of openness and portability plus the commercial performance of mainframes,'' said Mr McIntosh. The number standards to be supported by Windows NT still remains to be seen. Users of Digital's current UNIX operating system will easily migrate to the Digital OSF/1 system which will supersede Ultrix, but the company will continue to maintain Ultrix until then. Mr McIntosh said downsizing is the main trend today in the United States and Europe, whereas for users in Asian countries such as India, for example, Digital's attraction was firstly UNIX and then the Alpha's power and the easy portability of PC applications to Windows NT for the vast number of Asian PC users. According to Digital, more than 1,000 vendors are set to port their commercial, technical and scientific applications to the Digital OSF/1 operating system. Meanwhile the system is being tested by more than 2,000 users internationally.