Perhaps sensing an oncoming attack from the world's new #4 PC manufacturer, Acer, HP reached deep into its patent portfolio yesterday, uncovering five technology methods - including three acquired from Compaq - and filed a lawsuit accusing Acer of utilizing HP technologies covered by those patents without authorization. The suit seeks unspecified monetary damages, but more importantly, it requests that a judge block the sale of Acer computers utilizing those technologies, imported from Taiwan.

That could quite possibly include all of Acer's notebook line, since the technology addressed by two of the listed patents (one granted to Compaq pre-merger, one to HP post-merger) concerns processor speed reduction - the capability for a computer to instruct its processor to power down in periods of reduced stress or workload.

Processor "speed stepping," as some call it, is a fairly common feature today in portable computers. But in 2002, Compaq was granted one patent for a method in which processor speed can be stepped down, requiring some kind of a system that measures not just workload but the nature of processor activity. If a CPU appears to be doing the same thing repetitively - what's called a "tight loop" - it's probably just operating the mouse pointer and waiting for user input, a good time to power down.

Compaq's patent and the HP one that followed were careful not to refer to where this monitoring system would be located - for instance, in the BIOS or through an operating system driver. However, since neither company produces CPUs, it made sense to describe the system as independent from the CPU itself.

Clearly, however, if HP did invent this method of power consumption, it did not conceive the original method. Both Intel and AMD have adopted means for their CPUs to power themselves down in low-workload conditions. AMD incorporates such methods today under its "Cool 'n' Quiet" and "PowerNow" monikers; and Intel's SpeedStep technology - which borrows operating system drivers to manage workload - dates back to Windows 95, well before the 2002 issuance date on the Compaq patent.

But even excluding methods proffered by CPU manufacturers, Acer certainly isn't the only non-HP brand to employ power stepping. Apple has utilized it since at least the PowerMac G4 generation. And the fact that multiple methods may exist may go to the heart of whether HP was actually damaged by Acer's choice of methods. HP itself admits to having adopted AMD's Opteron power consumption methods for some servers in 2004.

So at least two of HP's five patents could face a significant challenge once its case comes to court.

While the other three patents in question may pertain to concepts that were original at the time, it may come as a surprise to more manufacturers than Acer that any sort of license from HP may be required to use them. For instance, in 2002, HP was issued a patent for the idea that, when writing data to a DVD+RW disc in multisession mode, subsequent sessions should be able to start writing at a certain fencepost bit where the previous sessions left off. This is in order to avoid frequency gaps caused by multiple sessions written by multiple devices, where a single reading device might not be able to reconcile the shift in one frequency to another in time to "see" the subsequent session.

Also under contention is a 1999 Compaq patent for the ability to segment signals traveling along a single digital bus into groups to facilitate different bus speeds; and a 1995 Compaq patent that was clearly written in the era before multicore processors were even considered. This oldest patent in the bunch is for a method for a BIOS to switch on multiple processors in sequence rather than simultaneously. At the time, the processors were assumed to be separate units; but nowadays, some of the language could very well apply to multicore CPUs, which now comprise a huge majority of sales in all markets.

That fact could play a role in Acer's defense, potentially arguing that, having inevitably foreseen the ubiquity of multicore processors, HP would have to have publicly stated its intention to defend this patent years ago in order for it to do so today. Network chip maker Qualcomm lost a similar argument against rival Broadcom just last week.

HP's suit was filed in federal court in Marshall, Texas, and seeks a jury trial. Marshall, a city of about 25,000, has become known in some quarters as the lawsuit capital of the US, reportedly handling 60% of all antitrust cases filed in the entire Eastern District.