The IBM System 305, the world's first computer with a hard drive, debuted in 1956 and relied on the random access method of accounting and control (RAMAC) to store data.
In 1971, IBM started shipping disks with a technology nicknamed Merlin that let the drive head track the platter much better. Prerecorded servo bursts help sync up the head and platters.
The Thin Film head debuted in 1979. Years later, the Giant Magneto Resistive head, invented by IBM, allowed for greater accuracy in positioning of data, which lead directly to improvements in areal density. You could stack up 250,000 of these heads and it would be less than an inch high.
The Hitachi Microdrives, with 1-inch diameter platters, were invented in 1999 by IBM, but didn't find a mass market until the arrival of iPod Minis. The microdrives from Hitachi contain platters that measure 1-inch across, while Toshiba has shrunk this to 0.85 inches.
In 1973, IBM introduced the 3340 "Winchester" disk system, the first to use a sealed head/disk assembly (HDA). Almost all modern disk drives now use this technology, and the term "Winchester" became a common description for all hard disks, though generally falling out of use during the 1990s. It was named after the Winchester 30-30 rifle after the developers called it the "30-30" because of its two 30 MB spindles.
Today, hard drives are found in excess of 400 Gb apiece. Most now use a new technology quickly catching on called SATA (Serial ATA), which can hit data transfer speeds of 150 mb/sec compared to ATA at 133 mb/sec. These hard drives use a technology to make multiple drives work in harmony with each other called RAID (Redundant Array of Independent (or Inexpensive) Disks), which simply means the drives work together instead of independent acting as one but still being separate. The two most common types are RAID 0 and RAID 1. RAID 0 stands for data striping, which allow them to have maximum performance by spreading out the blocks of a file across both drives, eliminating data redundancy, but at the cost of having slight instability where when one drive crashes, all the data is lost on both drives. RAID 1 stands for data mirroring, which means when one hard drive is written to, the other hard drive makes an exact duplicate, mirroring the other one so the two hard drives are identical, allowing for maximum security in case one crashes, allowing one to have a duplicate of the data reducing the chance of losing the data altogether, but the downside is the loss of an entire hard drive's worth of extra space for other information. Combined hard drives allow for storage up to 1 terabyte (1000 gigabytes). Normal drive speeds hover around 7,200 RPMs. Newer hard drives allow for speeds of 10,000 RPMs and 15,000 RPMs.
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