![]() ![]() These days, capacity is measured in gigabytes or terabytes. The capacity of a hard drive refers to the amount of data it can hold. At the moment these drives are very expensive per gigabyte. A new class of 2.5-inch high-speed drives has emerged that can be used in enterprise and server environments. Recent developments in 2.5-inch drives are changing how the small drives are used. This means they are better able to survive being shipped around or used in a moving environment. They need less power to spin so they can generally be bus-powered, meaning they can draw power from a laptop without the use of an external power supply.Īnd since they are designed to be portable, most of them do a better job of “parking the heads” than full-size drives do. They may have better “seek” times, since the read head has less distance to travel than with a larger diameter drive. They are physically smaller so they can fit in laptops and small portable enclosures.The smaller drives do have several advantages depending on the use. They also have a smaller data capacity and are more expensive per gigabyte. Newer 2.5 inch drives are also being used in high-performance storage devices.Ģ.5-inch drives generally spin slower which means that they have slower data throughput. 2.5 inch drives are used in laptops and portable storage devices. ![]() ![]() 3.5 inch drives, on the right, are used in desktop computers and in freestanding storage devices. Some compact desktops also use the smaller drives to enable a smaller form factor for the computer.įIGURE 2 shows the two sizes of drives generally in use. Traditionally, 2.5-inch drives are used for laptops while 3.5-inch drives are used for desktop computers. These sizes refer to the size of the data platters, not the size of the hard drive mechanism. Hard drives come in two basic physical sizes: 2.5-inch and 3.5-inch. Each drive also has a data interface: IDE/ATA or SATA for desktop drives, and Serial Attached SCSI (SAS) or Fibre Channel for enterprise drives. Hard drives have a power connector that provides juice for the motor that spins the drive and for the controller circuitry. It’s amazing that this is even possible, and even more amazing that it’s affordable.Ī hard disk drive also has electronics to control the mechanism, to translate the data to a format that can be written to the disk and to do error correction and analysis. The head skims back and forth at up to 10 meters/second and must stop on a line 1/10 the width of a human hair, and then correctly read the polarity of each bit. The magnets in a hard disk are organized in concentric circles - as many as 250,000 rings on a 3.5-inch platter. The read/write head moves like a record tone arm, and can flip the polarity of the magnet when it’s writing data, or read the polarity when it’s reading data. The polarity of each magnet can be “up” or “down,” which indicates whether the bit is a 1 or a 0. While the disk platter looks like a mirror, it’s actually composed of up to trillions of tiny magnets standing on end, arrayed in concentric circles. Figure 1 The inside of a hard disc drive, showing the disk platter and the read/write head. ![]()
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