6. Integrated RAM Controller, But Only For DDR-RAM In Single Channel Mode

The RAM controller that's integrated into the Turion 64 supports DDR200, DDR333 or DDR400 memory modules and single channel mode. Integrating the RAM controller in the CPU die noticeably reduces memory access latency times. That is most important when numerous memory accesses jump around the address space on multiple memory modules. In that case, simple memory bandwidth is seldom a determining factor. But when data is in adjacent memory domains, then memory bandwidth matters most. Memory bandwidth is a property of RAM module speed, and lies between 1.6 GB/s (DDR200) and 3.2 GB/s (DDR 400). Because the Turion can communicate with RAM directly over a dedicated interface, and not through a front side bus and a Northbridge interface as on the Pentium M, theoretically there's always sufficient bandwidth available to keep the CPU fed with data from the RAM.

Block diagram of AMD's Turion 64-Prozessor

Above all, performance consequences arise in this architecture when a processor must interact with a chipset that manages an integrated graphics controller and works with a shared memory architecture. In this situation, graphics data must shuttle relatively independently between RAM, the integrated memory interface in the CPU, through the hyper-transport channel to the PCIe connector, and from there to the graphics processor - here, there and everywhere, in other words.

In Intel's Pentium M, the theoretical maximum memory bandwidth of its memory interfaces is almost 8.5 GB/s. But because the FSB bandwidth of the CPU only goes as high as 4.2 GB/s, the Pentium M can't earn a performance win from the high bandwidth of dual-channel DDR2 RAM. You'll find a thorough background and measurements to back this up, in our article Sonoma: The Second Generation of Intel's Centrino Mobile Technology .

The Turion 64 RAM controller supports DDR memory modules - but not DDR2. This does have consequences for its use in notebook PCs. With its 1.8V power requirements, DDR2 demands about 30% less input voltage than latest-generation DDR RAM alternatives which still demand 2.5V. Higher input voltage also means noticeably higher power consumption and also higher current draw. These are all factors that weigh against extending battery life as long as possible.