The Sony VAIO Tap 21 (SVT21217CXB) is a large-screen portable all-in-one desktop PC, running Windows 8 multimedia benchmarks just as well as a high-end ultrabook. Its three-hour battery life is an improvement over the first generation of portable all-in-one desktops. The category is still evolving, but if you've figured out that you need a big honking screen that can be easily carried from room to room in your house, the VAIO Tap 21 is a decent choice.

Design and Features
The VAIO Tap 21 follows form and looks like a large slate tablet. It's built into and around its 21.5-inch screen, with an aluminum back and all-glass front. The system has a spring-loaded arm coming out of the back, which helps the system tilt from 15 degrees off vertical down to 90 degrees (flat). The arm doesn't have a latch to keep it closed, but the system's weight (8.43 pounds) will keep it closed when lying flat. This could be a problem if you rest the system on your lap, but on most tables and surfaces, the system will hold any angle you place the system in. The system is 1.4 inches thick, with 20.62 and 6.86 inches as its other dimensions. It's thicker and heavier than the thin Dell XPS 18, but is lighter than the HP Rove 20-K014us. All three all-in-one portable desktops are smaller and lighter than the pioneering Lenovo IdeaCentre Horizon, which is a 27-inch behemoth.

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The VAIO Tap 21 has a 21.5-inch, 1,920-by-1,080 resolution, 10-point touch screen. This feature and its pricing makes it an interesting alternative to a mid-size all-in-one desktop like the Editors' Choice Dell Inspiron 23 (2350) . The Dell Inspiron 23 has a larger screen and a bit more power and features, but the VAIO Tap 21's portability allows its users to just pick up the system and bring it to another room. This way, you can continue a presentation rehearsal in the conference room, or continue watching the movie you're watching in the kitchen. Another system that has this flexibility is the Asus Transformer AIO P1801, which uses an Android tablet as a remote display for the all-in-one desktop.

The VAIO Tap 21 has the benefit of bringing the PC hardware with you, so you don't have to trek back to the base station if you have a system crash or other problem. Plus, with the Asus Transformer, you'll have to manage and troubleshoot both an Android tablet and a Windows system if anything ever goes wrong. The screen is bright and clear, and 1080p online videos look great on the VAIO Tap 21's screen. About the only drawback to having such a large expanse of screen is that the glass is quite reflective.

The VAIO Tap 21 is easy to use as a humungous tablet, and it works very well with its included wireless keyboard and mouse. Tapping elements on the screen were responsive, so using Windows 8 and its evolving UI is easy. The system has a few UI ports for expansion, including a SD/MemoryStick card slot, HDMI out, two USB 3.0 ports, a headset jack, and Ethernet, all on the left side of the system. The system has a physical Windows button on the front, plus a NFC reader for use with NFC apps and peripherals. The bottom has a pair of plastic rockers, which help the system tilt smoothly, and prevents the bottom edge from digging into wood surfaces.

The system comes with quite a few pre-loaded apps, which include Intel AppUp, Finger Tapps Organizer, Puzzle Touch, Social Life, iheartradio, Crackle, My Daily Clip, Evernote Touch, Music Maker Jam, Pac Man Championship, Microsoft Office Trial, Family Paint, and Remote keyboard (for Sony products). The system also has a bunch of VAIO branded apps and utilities as well, notably VAIO Movie Creator and VAIO Tabletop. On the whole, most of these apps can be useful, but they do clutter up the Start Screen if you don't use them. The VAIO Tap 21 comes with a standard one-year warranty.

Performance
The VAIO Tap 21 has an Intel Core i7-4500U processor with Intel HD Graphics 4400, 8GB of memory, and a 1TB 5,400rpm SATA drive with 8GB Flash Cache. The flash cache and Core i7 processor means that the system is quick at coming back from sleep mode and at our benchmark tests. The system completes the Handbrake test in 1:14 and the Photoshop CS6 test in 5:03. This is slower than full-on desktops like the Dell Inspiron 23 (2350) and Asus Transformer, but is faster than other portable all-in-one desktops like the Dell XPS 18, HP Envy Rove 20-K014us, and even our aging slate tablets EC, the Microsoft Surface Windows 8 Pro ($999). The Dell XPS 18 has a larger cache drive, but a smaller hard drive, but the sum result is that the Dell is ever so slightly faster on the day-to-day PCMark 7 test. That said, you probably won't notice a difference when placed side-by-side. Since it has newer built-in graphics, the VAIO Tap 21 has better 3DMark numbers than the competition.