Guide to Western Digital’s GreenPower hard drive technology

Western Digital’s release of its GreenPower hard drive technology signalled another significant move by a major manufacturer into the provision of ‘green’ or environmentally friendly hardware. The GreenPower drives were made available in desktop, enterprise, CE and external hard drive implementations in capacities from 320 GB upwards. Western Digital’s claims are impressive: the boast power savings of 4-5 watts over competitors’ drives of similar sizes without suffering any degradation in performance. This 40% power saving, WD tells us, reduces CO2 omissions by 60kg over a year which is the equivalent of taking a car off the road for a fortnight. Naturally there is an associated cost benefit to the user, looking to be around $10/computer/year. Whilst this is small change to users with one or two machines around the home, the product’s savings may turn heads in enterprise applications where many hundreds of drives will be running constantly throughout the year. A trio of technologies were claimed by Western Digital in the implementation of the GreenPower drives to achieve this power saving: IntelliPower, IntelliPark, and IntelliSeek. IntelliPower describes the balance of spin speed, transfer rate and cache size. While this isn’t a new technology in itself Western Digital claim to have ‘found’ the optimum settings for each to ensure maximum energy efficiency without sacrificing speed. Interestingly Western Digital have chosen not to disclose the spin speed, transfer rate and cache size leaving critics questioning whether the reduction in power really meant a reduction in performance. IntelliPark ‘parks’ inactive cylinder heads, and to reduce aerodynamic drag on the spinning platters. IntelliSeek calculates seek speeds to reduce power consumption, noise and...

File systems (FAT, FAT8, FAT16, FAT32 and NTFS) explained

The precise manner in which data is organised on a hard disk drive is determined by the file system used. File systems are generally operating system dependent. However, since it is the most widely used PC operating system, most other operating systems’ file systems are at least read-compatible with Microsoft Windows. The FAT file system was first introduced in the days of MS-DOS way back in 1981. The purpose of the File Allocation Table is to provide the mapping between clusters – the basic unit of logical storage on a disk at the operating system level – and the physical location of data in terms of cylinders, tracks and sectors – the form of addressing used by the drive’s hardware controller. The FAT contains an entry for every file stored on the volume that contains the address of the file’s starting cluster. Each cluster contains a pointer to the next cluster in the file, or an end-of-file indicator at (0xFFFF), which indicates that this cluster is the end of the file. The diagram shows three files: File1.txt uses three clusters, File2.txt is a fragmented file that requires three clusters and File3.txt fits in one cluster. In each case, the file allocation table entry points to the first cluster of the file. The first incarnation of FAT was known as FAT12, which supported a maximum partition size of 8MB. This was superseded in 1984 by FAT16, which increased the maximum partition size to 2GB. FAT16 has undergone a number of minor modifications over the years, for example, enabling it to handle file names longer than the original limitation of 8.3...

Hard disk (hard drive) construction

Hard disks are rigid platters, composed of a substrate and a magnetic medium. The substrate – the platter’s base material – must be non-magnetic and capable of being machined to a smooth finish. It is made either of aluminum alloy or a mixture of glass and ceramic. To allow data storage, both sides of each platter are coated with a magnetic medium – formerly magnetic oxide, but now, almost exclusively, a layer of metal called a thin-film medium. This stores data in magnetic patterns, with each platter capable of storing a billion or so bits per square inch (bpsi) of platter surface. Platters vary in size and hard disk drives come in two form factors, 5.25in or 3.5in. The trend is towards glass technology since this has the better heat resistance properties and allows platters to be made thinner than aluminium ones. The inside of a hard disk drive must be kept as dust-free as the factory where it was built. To eliminate internal contamination, air pressure is equalised via special filters and the platters are hermetically sealed in a case with the interior kept in a partial vacuum. This sealed chamber is often referred to as the head disk assembly (HDA). Geometry Typically two, three or more platters are stacked on top of each other with a common spindle that turns the whole assembly at several thousand revolutions per minute. There’s a gap between the platters, making room for magnetic read/write head, mounted on the end of an actuator arm. This is so close to the platters that it’s only the rush of air pulled round by the...

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