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Toshiba’s crafty entering into the thin-and-light laptop computer world is timed for Windows 7, but if you are going to acquire one, make certain it is the dual-core T135-S1310, and not its single-core cousin.

How much of a difference does a single-core against dual-core ultralow-voltage C.P.U. make on a thin-and-light these days? You might not be paying attention under the hood–and that’s not your fault, since it is hard to discover the differences based on CPU name and Intel sticker-logos–but you should know that it makes quite a big difference indeed. Case in point: Toshiba’s new T135 thin-and-light, which we reviewed last week in its single-core configuration, the T135-S1300. For $599, we found it underpowered compared with its competitions, despite having very effective battery life.

Nevertheless, for only $100 more, the T135-S1310, which has a dual-core SU4100 processor, outperforms nearly every thin-and-light we have seen lately. For that $100 extra (plus $10 for a red or white Fusion Finish–which is what the company calls the high-gloss coating–instead of black), you not only get an Intel CULV that handles multitasking far better, but you also get an extra gig of RAM (and at a faster speed, too) and a 320GB hard drive instead of a 250. Simply put, the $699 Toshiba T135-S1310 is a no-brainer compared with its very similarly named cousin.

Although we still have issues with some of the design of the T135, and found the speakers to be very powerless, the T135-S1310 presents an first-class value point over the T135-S1300, and should be considered by anyone in the Windows 7 thin-and-light market. Just be sure you like the look and feel first.

From a occasional overview, the T135 series shares a number of design similarities to the rest of the Toshiba Satellite lineup that received an upgrade earlier this year. Covered inside and out in a glossy checkerboard Fusion Finish in either black, red, or white–ours was red, which, along with white, costs an extra $10–the T135 is accented with slick chrome highlights along the edge of the palm rest and on the touch-pad buttons. In fact, we liked the T135 better in red than we did in black. However, that slickness continues virtually to the keyboard, which is finished in the same glossy coating we’ve been less than enthusiastic about in other Satellites. While the T135 is thinner than Toshiba’s thick midrange Satellites such as the U505-S2940, it’s still a semi-chunky 1.4 inches thick.

The flat keyboard performs better than we recalled on larger Core 2 Duo models, but it still feels a little too greasy. The touch pad is a matte rectangle inset along the glossy palm rest, and feels decent but not spectacular. The silver button-bar beneath is one continuous piece of plastic that toggles on either side for left or right clicks, but we always choose distinct buttons instead. Other than the power button, there are no other buttons besides the standard keyboard, so control panel adjustments such as screen brightness are all handled with function-key combinations. Volume control is funnily relegated to a function combination with the 3 and 4 number keys, which took us forever to locate.

The 13.3-inch glossy LED-backlit screen on the Satellite T135-S1310 has a native resolution of 1,366×768 pixels, sharp colors, and good brightness, and it looked perfectly crisp in our use. Above the screen is a Webcam that took fair video, but grainy and low-resolution snapshots. More dissatisfactory were the Satellite T135-S1310′s speakers, which are stereo and planted on the base below the keyboard, but still sounded like they were emanating from the middle of a pillow-lined box: the volume at maximum was so soft and tinny, they were practically useless. We also had issues with Toshiba’s Netbook speakers, but other Toshiba speakers were generally exceptional. This was a big disappointment.