Xi3 Modular Computer with Tand3m Software, starts at $949; Lenovo IdeaCentre Q180, starts at $399 [Note: Scale is approximate. Products were not actually photographed together. Image is a composite.]

It just doesn't feel right calling a PC shorter than a soda can or the size of a paperback book a "desktop." But Xi3 and Lenovo both offer highly functional and space-efficient computers that are just that. Strictly in terms of volume, the IdeaCentre Q180 takes up about 25 percent less space. But which makes a better value may not be so clear-cut.

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In the short term, one ace up Xi3's proverbial sleeve is that at CES, they unveiled their $100 Tand3m software (slated for the first half of 2012 and included in the above $949 figure), which allows two people to share all the computing functions of one little Xi3. As with any desktop, each user would need their own separate monitor, keyboard and mouse. So, other than price — $400 per person for the Q180 vs. the virtual $475 per person for the Xi3 — how do the two compare?

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The Lenovo is meant more for the traditional consumer who wants to take advantage of the small footprint to enhance the richness of their multimedia TV experience. It's got an 8-in-1 card reader, integrated 802.11n Wi-Fi, USB 2.0 and 3.0 ports, and outputs for VGA and HDMI. Audio-wise, it supports 2.1 analog, plus 5.1 and 7.1 digital surround sound. It comes with a VESA bracket for mounting the PC on the back of your TV/monitor. And its full 3D/HD graphics support comes especially in handy with the optional Blu-ray drive that matches the Q180's size and magnetically sticks to it.

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The Xi3, on the other hand, is more for corporate and commercial installations looking to go green and save money. Or for more advanced, DIY-type consumer users. Not only does it save on materials and power consumption, but it's highly modular. So today your primary I/O module might sport six USB 2.0 and two eSATA 2.5 ports, with a mic and two headphone jacks. But tomorrow (figuratively speaking) you might want USB 3.0, eSATA 3.0 and some other configuration of audio channels. In other words, the Xi3 is future proof.

In the end, both teensy-weensy PCs offer plenty of brains, braun and options. Which is right for you depends on your particular goals and how long you plan to keep them. Either way, you can bank on taking up less space and using up less energy, which is no small thing.

Credit: xi3 Corporation, Lenovo

This article is part of our ongoing coverage of this year's Consumer Electronics Show. Find more CES articles here.