Jim recently moderated a seminar series on the topic of network and application optimization that was produced by Network World. This is the second of three newsletters that will discuss some of the questions that the audience had for the vendors that presented that the seminars.

Jim was surprised that one of the issues raised by the audience in each city was the return to the mainframe. For example, one attendee asked, “Isn’t the long term direction to move back to mainframe computing thereby eliminating WAN issues and most of us?” Another asked, “Would you say that with the implementation of VMware and virtualized data centers that we are going back to the days when we had only a mainframe?”

These questions seem to imply that we somehow have stopped using mainframes. The reality is that while mainframes are not as prevalent as they once were, we never stopped using mainframes. Many industries such as banking rely heavily today on mainframe computers.

That being said, there are indeed strong parallels between the IBM mainframes of the 1970s and 1980s and today’s virtualized data centers. In particular, the IBM mainframes of 20 years ago had powerful operating systems that supported virtualized processing and virtualized storage over the computer’s backplane. Given that architecture, it is reasonable to compare an IBM mainframe of that period with a contemporary data center that supports virtualized storage and processing over high-speed LANs and storage-area networks.

However, the phrase mainframe computing implies more than just the existence of a mainframe. That phrase also implies the type of desktop device and the types of applications that are run and the WAN connectivity. In the 1970s mainframe computing model the desktop device was a relatively dumb 3270 terminal. These terminals processed a standard set of applications that required virtually no bandwidth. In particular, the typical WAN of that timeframe was a 9600 baud, multi-point private line. Put another way, nobody ever sent a 10MB PowerPoint presentation over one of these networks.

In the current era of mainframe (or virtualized data center) computing, the desktop device can be a desktop computer, a laptop, or a wide range of PDAs or smart phones. These devices process a huge range of applications, some of which are provided by the company, and some of which are not. The WAN throughput requirements of these applications range from miniscule to monumental. The WAN itself is a combination of wired and wireless connectivity at speeds that typically range from sub-T-1 to OC-12. The movement to a service-oriented architecture with Web services drives one more distinction between 1970s mainframe computing and today’s mainframe computing. In the 1970s version of mainframe computing, the entire application resided on a single mainframe. In an SOA model, the application is comprised of multiple Web services that typically reside in different data centers.

Steve Taylor is president of Distributed Networking Associates and publisher/editor-in-chief of Webtorials. Jim Metzler is vice president of Ashton, Metzler & Associates.