Ask 20 people what a pervasive IT architecture is and you'll get 20 answers. Some will mention the rapid spread of always-on wireless and mobile devices. Others will focus on the coming proliferation of billions of tiny, IP-connected sensors, RFID tags, and monitoring devices. And some will think in terms of time rather than space, equating the concept of pervasive with around-the-clock operation.

But however you slice it, recent technology advances are pushing businesses into a world where anytime, anywhere access to people, applications, and data is becoming crucial to success - and it's clear that IT must design systems from the ground up with these requirements in mind.

"I have 2 million square feet of wireless coverage," says Dr John Halamka, CIO of both CareGroup Health System and Harvard Medical School. "I went for 100 percent coverage throughout the hospital so that I could enable workflow - anytime, anywhere access to data for clinicians who are truly mobile knowledge workers."

"It's all about getting information to the point of business when you need it," agrees Danny Shader, CEO of mobile software maker Good Technology. "Everyone's building networks on the assumption that it'll be IP everywhere," he says, noting that technologies such as WiFi, WiMax, 3G, and 2.5G virtually guarantee an always-connected business world. "It's not yet reliable, cheap, secure, or free, but its everywhere - people have spent billions on this," Shader adds.

"It's the death of the business day," says Jeff Schulman, VP of architecture at Gartner. "The old model was shutdown and batch catch-up; now it's seven by 24. There's a dynamism here that really pushes on our architectures. In real-time mode, there are responsiveness issues and issues around capacity."

Schulman also claims that in this pervasive future, everything will be addressable and the state of everything will be fully known. "If there is this level of profound connectivity, from an architectural standpoint, there's a very different level of managing resources, of understanding state, of process optimisation, and even of governance," he says. "And there's lots of privacy and security issues to be wrestled with."

How should enterprise architects prepare for this coming pervasive future? "Pervasive is a side effect of doing everything Web-exposed and middleware-driven," CareGroup's Halamka says. "My programmers these days are experts in the glue, which is what allows us to create what feels like an integrated product even though the parts may be very different."

In other words, leverage a unified back end to serve multiple channels, devices, and formats. "Most CIOs would like to have a pervasive presence for their customers that's consistent from an internal operations point of view, says Mike McCue, CEO of Tellme Networks, a provider of VoiceXML and VoIP-based outsourced services. McCue claims that, with 4 billion users world-wide, the phone is still the most pervasive device in existence and should be served not from proprietary voice systems but from the same IP-based Web infrastructure that can support tracking, personalization, and other rich functionality.

"The mobile device is the tail and not the dog," agrees Good Technology's Shader. "People don't want to deploy something custom, they just want to get a better R on the I they've already made - and the tools for doing that are standard operating systems, Web services, and composite applications."

Willy Chiu, vice president of high-performance on-demand solutions at IBM, adds that transformation technologies such as XML content style sheets should be built into architectures in anticipation of global deployments requiring different languages and domain-specific content. "Whether it's for an insurance broker doing claims adjustment, a broker trading on the stock market floor, or a real estate agent, pervasive systems can customise to those devices based on an underlying middleware layer, and transforming and assembling fairly open piece parts," Chiu says.