Hard Disk Drive Trends

The most amazing thing about hard disks is that they both change and don't change more than most other components. In terms of their basic design, today's hard disks aren't a lot different than the 10 MB clunkers installed in the first IBM PC/XTs in the early 1980s. However, in terms of their capacity, storage, reliability and other characteristics, hard drives have probably improved more than any other PC component. Let's take a look at some of the trends in various important hard disk characteristics:

• Areal Density: The areal density of hard disk platters continues to increase at an amazing rate even exceeding some of the optimistic predictions of a few years ago. Densities in the lab are now exceeding 550 Gbits/in², and modern disks are now packing as much as 375 GB of data onto a single 2.5" platter!

• Capacity: Hard disk capacity continues to not only increase, but increase at an accelerating rate. From 10 MB in 1981, we are now at 2TB in 2010 and will probably hit 3TB within a year for consumer drives.
• Spindle Speed: The move to faster and faster spindle speeds is likely to slow down now with the introduction of Solid State Disks (please see our guide here). Spindle speeds are important for both random-access and sequential performance. 7,200RPM spindle speeds are now the mainstream standard for 3.5" SATA II desktop drives; there are even 10,000RPM desktop drives available in the form of the Western Digital VelociRaptor. In the notebook 2.5" drive market, 4,200RPM drives have been phased out and replaced with the 5,400RPM, the most common speed; there are also numerous 7,200RPM notebook drives available. Server SAS server drives are now available up to 15,000 RPM.
  
• Performance: Both positioning and transfer performance factors are improving. The speed with which data can be pulled from the disk is increasing more rapidly than positioning performance is improving, suggesting that over the next few years addressing seek time and latency will be the areas of greatest value to hard disk engineers.
• Reliability: The reliability of hard disks is improving slowly as manufacturers refine their processes and add new reliability-enhancing features, but this characteristic is not changing nearly as rapidly as the others above. One reason is that the technology is constantly changing, and the performance envelope constantly being pushed; it's much harder to improve the reliability of a product when it is changing rapidly. The 4k sector is a great example of continuously improving hard disk reliability.
• RAID: Once the province of only high-end servers, the use of multiple disk arrays to improve performance and reliability is becoming increasingly common. Many mid-range and enthusiast PCs now ship with RAID available.
• Interfaces: From the IDE/ATA and SCSI interfaces of the 1990s and early 2000s, we have moved to simpler, faster, and more efficient SATA II and SAS interfaces. 

Next: Construction and Operation of the Hard Disk Drive