Where are Embedded PCs Heading?

by Peter Kannegießer

What is the difference between an embedded PC and a desktop PC? Functionally speaking, there is no difference at all - a PC is a PC is a PC. However, the definition that an embedded PC is one that cannot be seen from the outside as being a PC gives a very important criterion to discern the two: Reliability. If a standard desktop PC crashes, the normal reaction is to simply accept this incident and to reset the system using control-alt-delete or, in rare cases, even cycle the power.

An embedded PC, which usually is integrated within a complex hardware installation, cannot be considered with that much tolerance. Whether it is build into an kiosk ter-minal or an airport information system, a medical device or in a traffic supervision application, it must fulfill its duty flawlessly, 24 hours a day, 7 days a week. Since the desktop PC and the embedded PC share the very same chipsets and processors, the question about how to achieve this reliability pops up very fast.

Desktop PCs are built in vast numbers for the mass market and thus their designers are focused on cost-effective consumer market components. In this business, every saved cent makes a real difference. On the other hand, a desktop PC is optimized for a rather short lifetime only. This is quite different for embedded PCs. Complex sys-tems usually mean large investments that amortize only in the range of several years. It is impossible to change the computer platform each 12 or 15 month’ in such instal-lations. Deployment time and life expectations are at least 5 years in these cases.

Another reliability criterion is the fact that embedded PCs may need to endure large temperature changes, while the office or living room PC has a stable working envi-ronment. High reliability can only be reached by selecting suitable components (ac-tives, passives, connectors, etc), a not too critical circuit dimensioning and appropri-ate production processes (burn-in, run-in). Of course, all these measures have an impact on the cost. Quality and reliability cannot be had without investment.

A further issue that can be used to differentiate between embedded PCs and desktop PCs is their size. While there is a certain trend to shrink the desktop PCs, too, the size requirements on embedded PCs can be quite extreme. This has lead to the many different small form factor standards for embedded PCs - from PCI-104 to modular forms to miniature motherboards like mini-ITX.

Just a few years ago there has been a large performance gap between embedded PC and desktop PC performance. Today, these differences are no longer that large; except that the fastest desktop PCs may use up to and even more than 100 watts of power just for CPU and memory. Such huge power dissipation figures cannot be tol-erated in the embedded market, which consequently went to power-saving notebook. Like with embedded PCs, battery life time and little heat generation are main con-cerns for those. Thus, utilization of high-performance notebook processors allows for a new class of embedded PCs, having justifiable current consumption and reason-able thermal characteristics.

One of the first offerings using these components comes from LiPPERT; the Cool RoadRunner 4 is an embedded PC based on a 2 GHz Pentium M processor mounted a PCI-104 formatted board. The Pentium M 755 processor sports a 2 MB level 2 cache; the northbridge within the 82855GME chipset has an integrated high-performance graphics controller for analog displays and LVDS based flat panels. This, together with six USB 2.0 ports and a Gigabit Ethernet adapter mounted on a board the size of a beer mat, provides enough processing power even for complex and time critical applications. Running from a single 5 volt supply, the dissipated power is only around 25 watts.

This high-end solution is built in accordance with the PCI-104 standard; this new standard was adopted by the PC/104 consortium as an addendum to the older PC/104 and PC/104-Plus definitions. Because the traditional ISA bus connector is not needed with PCI-104, the thusly gained space opens a window to future PC tech-nologies like PCIexpress. In fact, the main difference between PCI-104 and PC/104 is the abandonment of the outdated ISA bus. Critics will protest, of course, pointing out to the huge existing market for PC/104 peripherals; not without cause, to be sure. However, when looking more closely, one will find that the solution for the peripherals issue is quite simple. For one thing, the Cool RoadRunner 4 with its sophisticated design and well-selected interfaces is highly interesting for applications where the ISA bus is not needed anyway. On the other hand, traditional interfaces like serial ports are available today as chip based solutions for the USB bus. Such offerings are steadily growing in number.

The system designer is forced to ask, why one should use an outdated and slow pe-ripheral bus for new designs when there are viable alternatives available as depicted above. Over and above this there is the upcoming RoHS (Restriction of Hazardous Substances) legislation to be considered; it will force many chip suppliers to clean up their product portfolio, which means they most probably will not offer ISA based com-ponents in a lead-free version. It seems to make more sense to abandon the ISA bus altogether and instead to define a connector that offers PCIexpress signals as well as USB 2.0 ports and possibly the LPC bus.

PCI-104 allows external system extensions with PCI based boards. A maximum of four peripheral boards may be used at one time. Together with Cool RoadRunner 4’s extensive on-board periphery, there is nothing left to wish for the system designer. Special function boards, like field bus interfaces, will become available over time, giv-ing an even larger choice for selection. Furthermore, certain functions could be con-nected to the PCI bus using FPGAs. And if there is still a real need for them, even ISA based functions can be integrated using LPC-to-ISA bridges.

Several processor classes from Pentium M 733 (1,1 GHz) to Pentium M 755 (2.0 GHz) allow the adaptation to the customer’s performance and economic require-ments as well as scaling the power consumption (from 14.5 to 27.5 watts). The boards may be passively cooled using a heat spreader and/or appropriate heat sinks, even at the highest possible clock frequency of 2 GHz. All facts considered, the Cool RoadRunner 4 again is a milestone for embedded PC technology and is conse-quently a safe investment over the next years for the system designer.

(Original appeared in Extension Media's PC/104 & PC/104-Plus Embedded Resource Catalog 2005)

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