The Western Digital Caviar GP is available in three capacity points : 1000 GB, 750 GB and 500 GB : the model numbers are WD10EACS, WD7500AACS, WD5000AACS respectively. The top model uses up to four platters at 250 GB per platter to reach its maximum capacity ; the 500 GB model hence is based on only two platters, which should make it the most energy-efficient drive. However, since the important fact is power per gigabyte, the possible power savings by using the 500 GB model instead of the higher capacity drives with the higher platter count are only interesting for very specific applications.
Western Digital uses spindle motors that can be dynamically adjusted to a certain spindle speed. This feature is called IntelliPower, and WD specifies the rotation speed at > 5,400 RPM, but also says that it dynamically allocates parts of the 16 MB drive cache memory.
There are also other features named with the "Intelli" prefix : IntelliSeek determines the optimum seek speed to meet acceptable performance while maintaining low power consumption (more power is required if the arms have to be accelerated and slowed down fiercely). IntelliPark moves the heads away from the surface of the platters to reduce aerodynamic drag. This feature can be compared to closing your windows when driving at 45 mph : it does make a difference in your gas mileage, though the difference is certainly small.
The remaining tech data is familiar : we already mentioned the 16 MB cache memory, there is a Serial ATA/300 interface with support for Native Command Queuing (NCQ) and it’s all packed into a standard 3.5" form factor case. The only thing that differentiates this drive from other WD models is its green sticker.