These hard drives are not meant to break new records in performance, but they might be able to break records when it comes to storage capacity per watt of power used. Both Hitachi Global Storage Technologies (HGST) and Western Digital have now released disk drives that cater to the power-conscious audience. The Hitachi Deskstar P7K500 and the WD GreenPower series reduce power consumption by up to 40% compared to conventional hard drives. We wanted to know what the impact on performance was of these design changes, which must not be significant for these products to be accepted in the market.
Looking at power requirements of 50 to 120 W for TFT displays, 20 to 120 W for processors, 25 to 200 W for discrete graphics solutions, up to 50 W for high-end motherboards and another 10 to 20% of the component power requirements due to losses in the power supply, a discussion of hard drive power requirements might seems of little interest. After all, the typical power consumption of a desktop hard drive lies anywhere between 5 and 15 W, depending on the model, spindle speed and platter count. In fact, choosing one drive or another does seem to have little impact on the power consumption of a desktop PC.
Yet the hard drive does have a measurable impact on power requirement in applications outside of a typical desktop PC environment: think of data centers, where thousands of hard drives are required to satisfy enormous storage requirements. And while any device not only consumes a certain amount of power when it operates, it is also produces heat that must be removed via air conditioning solutions. As a matter of fact, the effort and cost of deploying large-scale, fail-safe air conditioning solutions may be more significant than the direct cost and impact of device power consumption.
Other applications for low-power hard drives are consumer electronics devices such as personal video recorders (PVRs), set-top boxes with integrated storage, and all sorts of backup devices such as external hard drives and RAID-based solutions for near-line storage. These need to be as cool, quiet and as easy to maintain as possible, and they don’t even require great performance. Most of the hard drives that are integrated into consumer electronics products are actually still based on UltraATA interfaces rather than on Serial ATA.
Hitachi and Western Digital both have products to cater to these markets: the Hitachi Deskstar P7K500, where the P stands for “power”, and the Western Digital GreenPower series, which includes a number of power optimizations that can be found across various WD product lines.
There are two major items for consideration when you think of the power consumption of conventional hard drives. The first item is the power requirement of the mechanical parts: this includes the spindle motor, which is used to drive the physical platters, but also the actuator, which positions the read/write heads. More power is required to reach faster spindle speeds, and power requirements also depend on the diameter of the platters, the number of platters, and on the bearings used.
More power is also required to reach short access times, because the actuator may need to accelerate and decelerate quickly in order to move the heads from one surface location to the next. Again, the number of platters has an influence on actuator power requirements, as one actuator arm is needed to position every two heads (one on each side of each platter).
Performance features such as Native Command Queuing (NCQ) may contribute to saving power under load. NCQ lines up all incoming commands, analyzes them, and reorders them for execution in a way that minimizes head movement. However, NCQ is only really interesting in server-type environments.
The second major area of power consumption in a hard drive is the circuit board, which carries the controller, cache memory and interface logic. Increasing levels of integration have contributed to making the hard drive core logic more and more efficient. However, it still cannot be left out of the power equation.
Obviously, power savings can be achieved on the physical level, by reducing the spindle speed or by slowing down acceleration and break performance for the actuator. Optimizing the bearings is difficult, as most hard drives are already based on so-called fluid dynamic bearings (FDB). Deploying new, lighter materials can also help to reduce power consumption. However, robustness and reliability is an issue that must not be underestimated, and it’s hard to reduce parameters such as the thickness of a platter, due to the impact on other areas, such as ensuring smooth rotation. On the PCB side, it’s certainly possible to deploy power-saving mechanisms just like on other silicon components. Logic that isn’t being used, such as the cache memory, could be temporarily disabled.
Hitachi is close to releasing its next generation desktop hard drive, which is expected to replace the five-platter Deskstar 7K1000 with units using fewer moving parts. This could also bring an opportunity to update the energy-efficient product lineup, which, at this point, includes only capacities of up to 500 GB. Considering that efficiency is often measured by storage capacity per watt, this doesn’t put WD in front.
A hard drive that requires little power when it’s idle but doesn’t perform well might require more total power to complete a particular task than another product. Hence performance is also still important, because a particularly slow hard drive will counter its efficiency benefits through longer processing times at higher power consumption states.
There are four capacity points available: 500, 400, 320 and 250 GB. The latter are mainly interesting for PVRs and similar consumer electronics devices, as most of the hard drives in the PC desktop mainstream should provide at least 500 GB of capacity. Smaller capacities won’t provide much cost savings on a new PC, but will certainly result in insufficient storage capacity for the predictable future. However, Hitachi clearly targets the consumer market, as the Deskstar P7K500 is available with SATA or UltraATA interfaces, the latter of which still dominates the consumer storage market and the low end.
The P7K500 drives all rotate at the standard spindle speed of 7,200 RPM, while Western Digital decided to reduce speed in order to reduce power requirements. All UltraATA versions have 8 MB of cache memory, while the SATA versions (with the exception of the 250 GB entry-level drive) are equipped with 16 MB cache. The drives are based on a 250 GB per platter storage density, which means that the 250 GB model runs on a single platter, while all other capacities utilize two platters.
The Deskstar P7K500 is indeed much more efficient than other 3.5” hard drives running at 7,200 RPM: it consumed 4.7W of idle power, which is slightly more than the statement we found in Hitachi’s datasheet (4.5 W). While this power requirement is clearly higher than the results we measured for the Western Digital GreenPower drives, we found that the maximum power requirement is actually amazingly low at only 6.6 W—other 7,200 RPM drives easily require between 9 and 11 W when a lot of head movement is involved. This is also consistent with the “up to 40% operational power savings” stated by Hitachi. Note that the UltraATA hard drives are generally more efficient, as the parallel interface requires approximately 250 mW less power than Serial ATA connections.
Hitachi says that it used power saving technologies that were introduced on Travelstar notebook hard drives. This could be the reason for the long average access time of 18.7 ms, which is as much time as a 2.5” hard drive would take. However, it provides a good explanation as to why Hitachi maintains such low maximum power consumption.
Western Digital released so-called GreenPower hard drives for three different market segments, to address enterprise applications, desktop users and consumer electronics. The drives are available at 500, 750 and 1000 GB capacity points, and they carry the common product names such as Caviar, RE2 (RAID Edition 2) or AV (Audio/Video), but with the GP suffix. We took a look at two of the Caviar GP drives, which are designed for regular PC use.
We don’t really appreciate the obvious lack of information on the product page for GreenPower. WD talks a lot about environmental issues, but it failed to provide information on spindle speed even in the data sheet. Yes, there is 16 MB of cache memory and a 300 MB/s SATA interface, but the mandatory technical specs are missing.
Let’s look at the two drives we received.
WD5000AACS aka Caviar GP Green Power
Test Setup
| Processor(s) | 2x Intel Xeon Processor (Nocona core) |
| 3.6 GHz, FSB800, 1 MB L2 Cache | |
| Platform | Asus NCL-DS (Socket 604) |
| Intel E7520 Chipset, BIOS 1005 | |
| RAM | Corsair CM72DD512AR-400 (DDR2-400 ECC, reg.) |
| 2x 512 MB, CL3-3-3-10 Timings | |
| System Hard Drive | Western Digital Caviar WD1200JB |
| 120 GB, 7,200 RPM, 8 MB Cache, UltraATA/100 | |
| Mass Storage Controller(s) | Intel 82801EB UltraATA/100 Controller (ICH5) |
| Promise SATA 300TX4 | |
| Promise FastTrak TX4310 | |
| Driver 2.06.1.310 | |
| Networking | Broadcom BCM5721 On-Board Gigabit Ethernet NICv |
| Graphics Subsystem | On-Board Graphics |
| ATI RageXL, 8 MB | |
| Benchmarks | |
| Performance Measurements | c’t h2benchw 3.6 |
| PCMark05 V1.01 | |
| I/O Performance | IOMeter 2003.05.10 |
| Fileserver-Benchmark | |
| Webserver-Benchmark | |
| Database-Benchmark | |
| Workstation-Benchmark | |
| System Software & Drivers | |
| OS | Microsoft Windows Server 2003 Enterprise Edition, |
| Service Pack 1 | |
| Platform Driver | Intel Chipset Installation Utility 7.0.0.1025 |
| Graphics Driver | Default Windows Graphics Driver |
Data Transfer Diagrams



The Hitachi P7K500 and the WD7500AACS by Western Digital provide the highest minimum transfer rates at almost 50 MB/s. The WD5000AACS does well, but it drops to as low as 40 MB/s on the inner sectors of the platters.
Access Time

Clearly, Hitachi limits seek performance in an effort to keep maximum power consumption low. An 18.7 ms average access time is even slow for 2.5” hard drives. That’s not an issue for storage servers or consumer applications, but for desktop use, the WD drives provide clearly better access performance.
Interface Performance

The interface throughput is a mandatory test to verify the technical specifications, but it has little relevance to real-life performance. Interface performance is only interesting when the drive can read or write from or into the local cache memory.
Read/Write Throughput


Hitachi’s Deskstar P7K500 provides the best sequential throughput, as it runs at 7,200 RPM as opposed to 5,400+ RPM with Western Digital (the firm doesn’t provide detailed information). However, other 7,200 RPM drives such as the Seagate Barracuda 7200.11 or the Samsung Spinpoint F1 reach at least 100 MB/s, while Hitachi maxes out at 87 MB/s and WD is limited to 84 MB/s.




The energy-efficient drives clearly aren’t designed for I/O intensive workloads.


The WD GreenPower drives provide only 80% of the application performance other 7,200 RPM desktop drives show; the reduced spindle speed is obviously a disadvantage here. However, the P7K500 cannot deliver better file writing performance in PCMark05’s HDD benchmark.

A minimum idle power consumption of 3.1 W is a new record. WD’s WD5000AACS Caviar GP (500 GB) is the most energy-efficient drive, although it provided the lowest performance in this roundup. Hitachi’s 7,200 RPM spindle speed is a disadvantage, as the idle power is almost 50% higher! However, the Hitachi drive still is much more efficient than other 7,200 RPM drives, which consume 6+ W in idle.
Looking at maximum power consumption, Hitachi is even lower than the WD drives despite the higher spindle speed. If you remember the slow access times then you already know how this was achieved. If you want an efficient desktop drive, Hitachi offers the better performance per watt ratio, as the performance is clearly higher at similar power consumption results.
Surface Temperature

The drives do well when it comes to surface temperature. As expected, the WD drives, at less than 7,200 RPM, stay cooler than the 7,200 RPM Hitachi. Note that the WD VelociRaptor, which is on top at only 38°C surface temperature, is a 2.5” 10,000 RPM drive.
The Hitachi Deskstar P7K500 and the Western Digital Caviar GP both live up to expectations, as they both reduce average idle power consumption by up to 50% and maximum power requirements by 20% to 30%. This difference isn’t really important for home users, as the power savings of 3-5 W compared to regular 3.5” hard drives are negligible. However, consumer electronics devices, which you want to be quiet and cool, clearly benefit from such a drive. Large server deployments with hundreds or even thousands of hard drives will also show a noticeable impact due to reduced power requirements both for running the devices and cooling solutions. Also, users looking for a reasonable upgrade may consider such a drive as long as there is no price difference compared to other models. Hitachi also offers an upgrade option with the P7K500, as it is also available with the UltraATA interface.
Thanks to having kept the 7,200 RPM spindle speed, Hitachi offers superior transfer rates across all benchmarks, and overall decent desktop performance. However, access times and I/O performance cannot compete with other 7,200 RPM drives, as Hitachi slowed down actuator movements in order to save energy. This is why the P7K500 requires even less maximum power than the 750 GB and 1000 GB WD Caviar GP drives.
WD reduced the spindle speed from 7,200 RPM to somewhere in between this speed and 5,400 RPM, which results in a new record in power consumption: 3.1 W idle power for the 500 GB model and 3.6 W for the 750 GB Caviar GP are excellent results. Should you be looking for one or even several efficient storage hard drives, the Caviar GPs will be the best choice. Hitachi, however, is the better choice if you also want to use the energy-efficient hard drive to hold your operating system.
Comparison Table
| Manufacturer | Hitachi | Western Digital | Western Digital | Western Digital |
|---|---|---|---|---|
| Model | Deskstar P7K500 | Caviar GP | Caviar GP | Caviar GP |
| Model Number | HDP725050GLA380 | WD5000AACS | WD7500AACS | WD10EACS |
| Form Factor | 3.5" | 3.5" | 3.5" | 3.5" |
| Capacity | 500 GB | 500 GB | 750 GB | 1000 GB |
| Spindle Speed | 7200 RPM | > 5400 RPM | > 5400 RPM | > 5400 RPM |
| Other Capacities | 250, 320, 400 GB | 750, 1000 GB | 500, 1000 GB | 500, 750 GB |
| Platters | 2 | 2 | 3 | 4 |
| Cache | 8 MB | 16 MB | 16 MB | 16 MB |
| NCQ | yes | yes | yes | yes |
| Interface | SATA/300 | SATA/300 | SATA/300 | SATA/300 |
| Warranty | 3 years | 3 years | 3 years | 3 years |









