Using rigid disks and sealing the unit allows much tighter tolerances than in a floppy disk drive. Consequently, hard disk drives can store much more data than floppy disk drives and can access and transmit it faster. In 2007, a typical “enterprise”, i.e. workstation HDD, might store between 160 GB and 1 TB of data (as of local US market by July 2007), rotate at 7,200 or 10,000 revolutions per minute (RPM) and have a media transfer rate of 1 Gbit/s or higher. [9] The fastest “enterprise” HDDs spin at 15,000 rpm, and can achieve sequential media transfer speeds above 1.6 Gbit/s.[10] Drives running at 10,000 or 15,000 rpm must use smaller platters because of air drag. Mobile, i.e., laptop HDDs, which are physically smaller than their desktop and enterprise counterparts, tend to be slower and have less capacity. In the 1990s, most spun at 4,200 rpm.[11] In 2007, a typical mobile HDD spins at 5,400 rpm, with 7,200 rpm models available for a slight price premium.
The exponential increases in disk space and data access speeds of HDDs have enabled the commercial viability of consumer products that require large storage capacities, such as digital video recorders and digital audio players.[12] In addition, the availability of vast amounts of cheap storage has made viable a variety of web-based services with extraordinary capacity requirements, such as free-of-charge web search and email (Google, Yahoo!, etc.).
The main way to decrease access time is to increase rotational speed, while the main way to increase throughput and storage capacity is to increase areal density. A vice president of Seagate Technology projects a future growth in disk density of 40% per year.[13] Access times have not kept up with throughput increases, which themselves have not kept up with growth in storage capacity.
As of 2006, some disk drives use perpendicular recording technology to increase recording density and throughput.[14]
The first 3.5" HDD marketed as able to store 1 TB was the Hitachi Deskstar 7K1000. It contains five platters at approximately 200 GB each, providing 935.5 GiB of usable space.[15] Hitachi has since been joined by Samsung (Samsung SpinPoint F1, which has 3 × 334 GB platters), Seagate and Western Digital in the 1 TB drive market.[16][17]
Form factor Width Largest capacity Platters (Max)

5.25" FH	146 mm	47 GB[18] (1998)	14
5.25" HH	146 mm	19.3 GB[19] (1998)	4[20]
3.5"	102 mm	1 TB[15] (2007)	5
2.5"	69.9 mm	500 GB[21] (2008)	3
1.8" (PCMCIA)	54 mm	160 GB[22] (2007)
1.8" (ATA-7 LIF)	53.8 mm
1.3"	36.4 mm	40 GB[23] (2008)	1

[edit] Capacity measurements

The capacity of an HDD can be calculated by multiplying the number of cylinders by the number of heads by the number of sectors by the number of bytes/sector (most commonly 512). Drives with ATA interface bigger and more than eight gigabytes behave as if they were structured into 16383 cylinders, 16 heads, and 63 sectors, for compatibility with older operating systems. Unlike in the 1980s, the cylinder, head, sector (C/H/S) counts reported to the CPU by a modern ATA drive are no longer actual physical parameters since the reported numbers are constrained by historic operating-system interfaces and with zone bit recording the actual number of sectors varies by zone. Disks with SCSI interface address each sector with a unique integer number; the operating system remains ignorant of their head or cylinder count.
The old C/H/S scheme has been replaced by logical block addressing. In some cases, to try to "force-fit" the C/H/S scheme to large-capacity drives, the number of heads was given as 64, although no drive has anywhere near 32 platters.
Hard disk drive manufacturers specify disk capacity using the SI prefixes mega-, giga- and tera-, and their abbreviations M, G and T. Byte is typically abbreviated B.
Some operating-system tools report capacity using the same abbreviations but actually use binary prefixes. For instance, the prefix mega-, which normally means 106 (1,000,000), in the context of data storage can mean 220 (1,048,576), which is nearly 5% more. Similar usage has been applied to prefixes of greater magnitude. This results in a discrepancy between the disk manufacturer's stated capacity and the apparent capacity of the drive when examined through some operating-system tools. The difference becomes even more noticeable (7%) for a gigabyte. For example, Microsoft Windows reports disk capacity both in decimal-based units to 12 or more significant digits and with binary-based units to three significant digits. Thus a disk specified by a disk manufacturer as a 30 GB disk might have its capacity reported by Windows 2000 both as "30,065,098,568 bytes" and "28.0 GB". The disk manufacturer used the SI definition of "giga", 109 to arrive at 30 GB; however, because the utilities provided by Windows define a gigabyte as 1,073,741,824 bytes (230 bytes, often referred to as a gibibyte, or GiB), the operating system reports capacity of the disk drive as (only) 28.0 GB.

Contents:

• 1 Main page of hard drive
• 2 Technology
• 3 Form factors
• 5 Access and interfaces
• 6 Integrity
• 7 Manufacturers