Intel is to update its Core Duo processor line, the chip maker has told customers, with samples of new T2400, T2500 and T2600 65nm dual-core processors shipping by early May. Some may go out the door before the end of April, we understand.

According to company documentation seen by Reg Hardware, the move will see Intel replace the three processor's C-0 core stepping with an update version dubbed D-0. The scheme will affect both boxed and tray-sold CPUs, with shipments of commercial product commencing 23 June.

At this stage, it's unclear what the core update involves beyond the broad "speed enhancements" Intel mentions in its documentation. D-0 Core Duos are backwards compatible with C-0 parts, though the new core will require a BIOS update, Intel warned.

The chip maker also said it will update Core Solo and Celeron M 400 series processors in due course - even though it has yet to ship a Celeron M 4xx CPU.

As we exclusively revealed in January, Intel is preparing three initial Celeron M 4xx parts: the 410, 420 and 420, clocked to 1.46GHz, 1.60GHz and 1.73GHz, respectively. All three are fabbed at 65nm and based on the 'Yonah' core. There's also a Low-Voltage 65nm Celeron M, the 423, in the works. It's clocked at 1.06GHz. All four chips use a 533MHz FSB. They're due to ship in the current quarter. ®