The "brains" inside the next generation of advanced digital set-top boxes will be any one of a number of small, sophisticated operating systems that fall within the burgeoning category of "embedded applications." For now, PowerTV, the operating system chosen for Time Warner's Pegasus box, and Windows CE, the OS apparently selected by Tele-Communications Inc. for its digital set-tops, have captured a large portion of set-top OS mindshare. But there are several other embedded application OSs suitable for set-tops, including Microware Systems Corp.'s OS-9, Sun Microsystems Inc.'s JavaOS for Consumers and Sony Corp.'s Aperios, which TCI in July selected as an "alternate" OS for its set-tops.

Outside of the General Instrument/Scientific-Atlanta orbit of set-top box configurations, Motorola will be using Microware's OS-9-based DAVID (Digital Audio/Video Interactive Decoder) as the OS for its Blackbird multimedia architecture, and Sunnyvale, Calif. startup TiVo's "content receiver" will run Linux, a Unix-based OS that's riding a strong wave of popularity in the networking world.

Suffice to say there are enough possible set-top box OS applications on the market to rule out a de facto monopoly by any single OS, at least in the near future. "The consumer electronics industry," says Arthur Orduna, director of marketing for Microware, "is not enabling a Microsoft-like monopoly."

More importantly, there is enough OS intelligence on the market to keep digital set-tops slim, inexpensive and agile even as (or if) cable subscribers demand more and more digital and interactive services.

The industry is a long way from picking winners and losers. As Jim Chiddix, chief technology officer for Time Warner Cable points out, "The installed base of sophisticated set-top boxes right now is zero." That will soon change.

Lean and mean set-top box OSs, while able to handle sophisticated tasks in real time, are much leaner in size than full-blown PC OSs but are tuned to respond to demanding network protocols and instructions, such as those delivered on an RF cable plant.

"The core functionality of the OS will always be small," says Gideon Yefet, manager of OS software development for PowerTV. "It will not grow up to be a PC-type OS."

Smaller does not mean unsophisticated, however. A basic feature of embedded systems OSs is that a minimal amount of user input is required to execute commands in real-time. However, as Orduna notes, "the simpler the interface, the more demanding the technology behind it."

A set-top OS is born

PowerTV, by virtue of the fact that Time Warner Cable, MediaOne, Comcast, Cox Communications, Adelphia Communications, Marcus Cable, Cogeco, Rogers Cablesystems and Videotron are already deploying set-tops with its OS, now enjoys the highest profile of any set-top box OS. PowerTV came about in 1994 when Scientific-Atlanta provided seed money for a group of engineers from Kaleida Labs to create an OS for advanced TV. The OS became PowerTV, and the company became a partially owned subsidiary of Scientific-Atlanta.

PowerTV is now at version 1.5, and according to Yefet, version 2.0 is due in January of next year. In addition to the functionalities of version 1.5, PowerTV 2.0 will include a Window Manager, which will allow multiple applications to share a screen; Session Manager Extensions, which provide support for dedicated nework resources such as video-on-demand; and a Service Application Manager, which handles applications, such as a Web browser or channel navigation application, with specific sets of data that may be associated with a channel number.

According to Yefet, FireWire (IEEE 1394) and Universal Serial Bus (USB) support in the PowerTV OS are under consideration for versions beyond 2.0.

The power of Windows

"When you choose an operating system for a set-top box," says Steve Guggenheimer, group product manager, digital television, for Microsoft Corp., "it's important to plan for the long term." Windows CE is not only a bit larger in memory than most embedded systems OSs, it also flexes the most muscle in terms of installed base of PC-based personal information devices and entertainment consoles.

The strength of Windows CE, says Guggenheimer, is the significant support the OS already enjoys with microchip and peripheral manufacturers, and software providers who are writing applications and content for Windows CE. He also cites the natural CE compatibility for Microsoft's DirectX programming interface, which supports advanced graphics, sound, video and networked games.

An example of DirectX and CE's power in the marketplace is the fact that Microsoft will provide a customized version of CE with DirectX services enhanced for console-style gaming for Sega's new video game machine, Dreamcast. CE is also the preferred OS for a number of handheld and palm-style computers. Microsoft touts the Win32 API, which CE embraces, as the "world's most widely used programming model."

"Futureware" is a term that Guggenheimer uses when describing CE, meaning that CE developers and users are "leveraging a known infrastructure." In fact, CE supports an array of functionalities, including voice and handwriting recognition, stylus/pen input, and connectivity with IR devices, Ethernet and dial-up services. "You can mix and match these functionalities" with CE, said Guggenheimer.

In addition to its anticipated roll as a set-top box OS, Windows CE will soon become the OS for the WebTV Plus Receiver.

DAVID and Goliaths

Motorola's choice of Microware's DAVID was a boost for the OS, which, according to Orduna, is in use in both telecom and HFC systems in New Orleans, Hawaii, California, New Jersey, Canada, Hong Kong, Tokyo, northern Japan, southern China and Europe.

DAVID OS architecture

OS-9 comprises the real-time OS, the kernal, of DAVID, says Orduna. The components of DAVID include an interface for advanced graphics, MPEG and Java support, plus an input control module, file system module, and an interface for network protocols, including SNMP, IP and ATM. ATSC and DVB compliance are also components of DAVID.

Orduna differentiates DAVID from the crowd by its Java support, explaining that Microware was the first embedded systems real-time OS company to license Java and include it in a deployed set-top box—NEC's set-tops used by Hong Kong Telecom IMS. "The more that Sun pushes Java," says Orduna, "the better it is for us."

The Java marketing machine is a significant counter to Microsoft's muscle, as both Java and CE are in many ways trying to offer the same thing - one OS that will run many applications.

Orduna also claims DAVID can run on any headend conditional access scheme. After Scientific-Atlanta chose to create its own OS (PowerTV), "we were forced to partner with everyone else," says Orduna.

In the wings

Sony's Aperios, according to company spokesman Mack Araki, will be incorporated into a satellite receiver for Japanese satellite broadcaster SkyPerfecTV - the only application of Aperios so far. No specific details of Aperios were made available.

When Sun Microsystems acquired Diba Inc. last year, it incorporated Diba's ChorusOS, a real-time embedded systems OS, into JavaOS for Consumers. Combined with PersonalJava, the applications environment chosen by TCI for its set-tops, Sun can offer a strong OS/application environment solution for set-top boxes.

Clearly, the battle lines and alliances in the war for the set-top box OS are continually shifting and far from settled.

Watching the battle, Chiddix, for one, seems less-than-anxious about which OS Time Warner deploys in future incarnations of its set-top boxes. "Philosophically, we like to be basically agnostic about the operating system of the set-top box," says Chiddix. More important for him are middleware applications, which can ensure that the new generation of services are interoperable.

"The point of that strategy," says Chiddix, "is to not to have to care about the operating system."


The memory footprint of the PowerTV OS version 1.5
ROM — 1.1–1.2 MB (operating system)
Flash — 128k (operating system patches: feature changes and bug fixes)
DRAM — 100k (system memory for network buffers, stacks for threads, initialized variables, etc.)
Enabling functionality
Analog broadcast (non-secure) Analog pay-per-view Digital broadcast (non-secure) Digital pay-per-view Electronic program guideAnalog broadcast (secure) Analog impulse pay-per-view Digital broadcast (secure) Digital audio broadcast Client/server interactive application download


Windows CE OS

  • Win32 API subset, file system, memory management, communications protocol, choice of development tools.
  • Processor support: x86, PPC, MIPS, ARM/Strong ARM, SHx
  • Footprint: 40KB RAM, 256KB persistent storage
General features
  • Modular operating system, where some modules are also componentizable
  • Built in support for communication, the Windows CE shell, and device drivers
  • Subset of Win32 API set and familiar development model and tools for application developers
  • Easy adaptation to many kinds of devices and memory ranges