18. System RAM

Many users don't fully appreciate the energy savings potential that RAM can offer to a system designer. But there are good reasons why many sub-laptop builders solder some of the system RAM right onto the motherboard. This is also true in the Sony TX laptops.

The TX series laptops include 512 MB of (non-removable) RAM soldered onto the motherboard.

To keep the energy consumption of this key system building block to a minimum, Sony solders 512 MB of RAM right onto the motherboard. This lets system designers control which memory chips remain active and powered up, and also reduces the resistance that current must ordinarily overcome to flow through a socket into a discrete memory module. Though this usually only involves something in the milliohm range for memory slots and their associated modules, a hard-soldered memory connection nevertheless affords some slight energy savings in laptop design. Also, sockets for SO-DIMMs (small outline, dual in-line memory modules) exhibit higher resistance, which raises the power consumption of these memory modules further compared to hard-soldered modules. In addition, the longer leads that a SO-DIMM socket uses require more expensive, power hungry switching circuits and drive power consumption levels up still further. In total, our test laptop included 1 GB of RAM, where up to 128 MB was shared with the Intel GMA900 graphics chipset.

The DDR2 memory modules in the TX series run in the slower single channel mode, even though the chipset can handle faster dual channel mode operation.

Naturally, a question we wanted to answer was how many minutes of additional battery life we could get by doing without the additional, plug-in SO-DIMM module. You'll learn more about this topic later, when we present our battery life test results (Mobilemark 2005).