Squeezing More Life Out of Your Notebook's Battery Part II

Mobile CPUs Are Always Faster, But Not Noticeably More Energy-efficient

Although both AMD and Intel talk a good game about wanting to curb the energy appetites of their mobile processors, power consumption in processors of late has certainly not decreased. This phenomenon occurs thanks in part to Moore's Law, which leads to inexorably higher transistor counts in each new processor generation. This also occurs despite noticeably reduced processor die granularity (with 90-nm and emerging 65-nm production processes) and improved chip production techniques. The "Gigahertz races" have not yet completely run their course yet either, as the following examples should illustrate:

Intel's Pentium M processor.

A mobile Pentium III-M 1.3 GHz built in 2003 held a Thermal Design Power (TDP) rating of 22 watts. Cooling systems and batteries in notebooks with a mobile Pentium 4-M 2.66 GHz had to deal with 35 watts of heat dissipation and power consumption instead. The TDP of a first-generation 1.3 GHz Pentium (4-) M CPU with 1 MB of L2 Cache was also rated somewhere around 22 watts. But the current top-of-the-line Pentium M 780 with 2.26 GHz consumes up to 27 watts, according to the maker's data sheets. If this actually represents real maximum power consumption or not is unclear. A detailed examination of the various definitions for TDP as stated by different sources indicates that this may not be the case. Ask yourself this as well: how can the different data sheets for mobile Pentium III-M and Pentium M processors show the same values for presumably different processors, with typical generation gaps (higher device counts, bigger chips and so forth)?

AMD's Turion 64 processor.

Where power consumption for AMD's mobile CPUs is concerned, things look no better. Products of the recent past, such as the Athlon 64 2800+ suck up as many as 82 watts, while newer models such as the Mobile Athlon 64 3200+ slimmed down a bit to 62 watts. The new Turion 64 models, on the other hand, lay claim to a TDP rating in a range from 25 to 35 watts. But by comparison to the serviceable old Mobile Athlon XP-M models with a TDP of 25 watts, there really hasn't been any noticeable improvement in their mobile offerings, either.

Overview of maximum power consumption for current AMD and Intel CPUs

To prevent CPUs from sucking batteries dry on their own, both CPU vendors deliver "intelligent" energy saving mechanisms, which don't differ much from each other in terms of capabilities or functions.

Except for Intel's Celeron M, all mobile processors support energy-saving operation, which permits them to adapt their clock rate (and their power consumption) to meet current processing demands.

AMD calls this feature PowerNow, while Intel's counterpart is called SpeedStep. With both of these processes, the CPU incrementally and automatically adjusts its core speed and voltage to the performance required by the currently running applications. If more performance is needed, the clock speed and core voltage go up. If less performance is needed, then both of these variables decrease again.

Then too, Intel is the competitor whose built-in energy saving mechanisms provide most grounds for consideration. For one thing, only the part of the L2 Cache in the Pentium M processors that is in use remains active. Also, this CPU has IMVP at its disposal. This acronym stands for Intel Mobile Voltage Positioning. Hereby The input voltage to the processor's core thus fluctuates in discrete steps when the CPU-core is loaded. AMD's mobile CPUs keep the entire cache active at all times, thereby increasing overall power consumption. In addition, AMD's mobile components work at individual, discrete voltage and clock rate settings known as p-states, and maintain constant core voltages.