Eight months ago Intel rocked the mobile processor world with its first dual-core CPUs, which in our tests outpaced a similarly configured laptop running on a single-core processor by 30 percent when performing two tasks simultaneously. Now comes Core Duo's successor, Core 2 Duo, with claims of even better performance plus 64-bit support. Should you be kicking yourself for jumping the gun and buying a Core Duo notebook earlier this year?

PC World tests indicate that you shouldn't sweat it too much. Whereas Core 2 Duo desktops racked up dramatically higher test scores than their Pentium D--based counterparts, notebooks got only a small performance boost from the mobile Core 2 Duo (formerly code-named Merom). Battery life for comparable products was similar.

The latest descendants of Intel's Centrino-CPU-and-wireless-chip-set combination, Core 2 chips fall into two lines: the T5000 line, which includes the 1.66-GHz T5500 and the 1.83-GHz T5600; and the T7000 line, which features 2-GHz (the T7200), 2.16-GHz (the T7400), and 2.33-GHz (the T7600) models. (Intel says that it will produce low-voltage and ultra-low-voltage Core 2 Duo CPUs for the smallest ultraportables by summer 2007 and the end of 2007, respectively.)

Core Duo vs Core 2

Like their Core Duo predecessors, Core 2 Duo processors have a 667-MHz frontside bus, a 945 chip set, and a 3945ABG wireless chip set. The two most significant improvements are the doubling of Level 2 cache to 4MB (in the T7000 line) and support for 64-bit processing. The latter brings Intel's Core 2 Duo up to par with AMD's Turion 64 X2.

We tested three Core 2 Duo--based notebooks: a US$1906 Dell XPS M1210 equipped with a 2-GHz T7200 chip; a $2164 Gateway M685-E desktop replacement with a 2.16-GHz T7400 chip, and an all-purpose $1499 HP Pavilion dv6000t with a 1.83-GHz T5600 chip. The biggest performance increase over laptops with same-speed Core Duo CPUs was 7 percent--enough to shave a few seconds off day-to-day business operations, but nothing more.

No big battery gain

In our tests, Core 2 Duo didn't affect battery life much. The Dell, carrying a 12.1-inch wide-screen LCD and a 9-cell battery, did best here, running for 4 hours, 23 minutes.

Core 2 Duo chips cost the same as Core Duos used to, so you can expect fire sales as Intel begins to discount the older Core Duo chips. In view of the modest performance gains, shoppers should think long and hard before paying a premium for a Core 2 laptop.