Hard Disk (Hard Drive) Performance – transfer rates, latency and seek times

The performance of a hard disk is very important to the overall speed of the system – a slow hard disk having the potential to hinder a fast processor like no other system component – and the effective speed of a hard disk is determined by a number of factors. Chief among them is the rotational speed of the platters. Disk RPM is a critical component of hard drive performance because it directly impacts the latency and the disk transfer rate. The faster the disk spins, the more data passes under the magnetic heads that read the data; the slower the RPM, the higher the mechanical latencies. Hard drives only spin at one constant speed, and for some time most fast EIDE hard disks span at 5,400rpm, while a fast SCSI drive was capable of 7,200rpm. In 1997 Seagate pushed spin speed to a staggering 10,033rpm with the launch of its UltraSCSI Cheetah drive and, in mid 1998, was also the first manufacturer to release an EIDE hard disk with a spin rate of 7,200rpm. In 1999 Hitachi broke the 10,000rpm barrier with the introduction of its Pegasus II SCSI drive. This spins at an amazing 12,000rpm – which translates into an average latency of 2.49ms. Hitachi has used an ingenious design to reduce the excessive heat produced by such a high spin rate. In a standard 3.5in hard disk, the physical disk platters have a 3in diameter. However, in the Pegasus II, the platter size has been reduced to 2.5in. The smaller platters cause less air friction and therefore reduce the amount of heat generated by the drive....

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