4. FSB And DDR2 Faster; Dual-channel Operation As Well

Another important innovation that deserves mention is the increase in the CPU's front side bus (FSB). With new Dothan models, it's now clocked at 133 MHz, which is a 33% increase. Consequently, peak bandwidth of the CPU interface jumps by a third as well, from 3.2 GB/s to 4.2 GB/s. Of course, a higher FSB makes sense only when combined with faster main memory (RAM) that enables higher peak bandwidth. The first generation Centrino chipset, 855GME, only supported single-channel operation with DDR 333 memory and a peak bandwidth of 2.6 GB/s. For the new platform and its higher peak bandwidth, a DDR2 interface was absolutely necessary to avoid having the CPU wait on the main memory to deliver data. Intel decided to support DDR2 memory with speeds up to 533 MHz and dual-channel operation. As the following table shows, in single channel operation the DDR2 533's bandwidth would be sufficient to keep the CPU happy with enough data flow - at least when working with a dedicated graphics solution.

The situation is different when we consider an integrated graphics core. In that case, an insignificant part of the memory bandwidth is "spent" on processing screen content. The graphics core dynamically allocates, depending on the settings in the BIOS system and drivers, up to 224 MB of RAM for the processing of video data. In this case, based on calculations alone, dual-channel operation with doubled maximum bandwidth of 8.5 MB/s makes sense.

In addition to the higher bandwidths that DDR2 enables, other factors also speak in favor of using this memory technology in a notebook. DDR2's supply voltage is only 1.8 volts, around 30% lower than that of DDR. As a result, DDR2 modules use less power, conserving battery life, and do not heat up as much, which favors a more simplified thermal design. An additional advantage of DDR2 is better signal quality due to the on-die termination, and considerably better compatibility of the modules with various notebooks.

Countering these advantages is the fact that the memory controller runs two modules and is therefore more expensive due to obsolescence costs, as well as the fact that it uses more power. Users of DDR2 will also see higher costs when purchasing and upgrading because DDR2 memory modules are still more expensive than standard DDR.