What is a hard disk?

Despite the fact that even at school lessons in computer science the teacher explains what a hard disk is, a similar question is frequently asked in the global web . Some listened to the explanations inattentively, others were not interested. In this article, we recall the long-forgotten - tell you what a hard drive is.

Why, in fact, the disk is called hard? This term originated at the dawn of development Computer technology, when punch cards have already given way to magnetic tapes and floppy disks, and CDs have not yet appeared. Probably, many modern computer owners do not even know what floppy disks are and how they looked. But without considering them, you can not give an answer to the question of what a hard disk is. Magnetic tapes (as in audiocassettes) as a carrier of digital data did not last long - the film's footage did not allow to quickly find the desired area. They were replaced by floppy disks. They were polymeric discs, covered with a magnetic layer on both sides. It can be assumed that the tape of the cassette was simply melted into a disc. To protect it from scratches, it was placed in a square shaped opaque plastic envelope - a floppy disk was produced. The data was read by the drive. The strength of the floppy disk was small - it could easily be bent (the form was restored) and even folded in half. Both the first and the second could not be done - this led to errors in the surface due to damage to the magnetic layer (especially when bending). What's important is that the floppies are called GMDs - flexible magnetic disks.

At the same time, special electromechanical devices, which are a metal or glass disk with magnetic deposition (chromium oxide), rotated by a motor in a casing at a constant speed, have spread. The electronic part on the loop received read / write control commands from Computer. Differences from floppy disks were the following: much larger volume, high reliability, performance, impossibility to bend, because the case, and the disc itself was metal.

What is a hard drive? This is the above device - HDD (hard disk based drive). Other names - HDD, hard drive, etc.

Modern hard disks contain several disks on a common axis, which allows to increase the total volume. Unlike cassettes, the reading head does not touch the surface during operation, but flies on the air layer (no more than 10 nm). The speed depends on the speed of rotation: the most productive server models spin disks up to 15,000 rpm, the secret standard is 7200, and the economical versions are "content with the modest" 5400. Although recently there have appeared intelligent HDDs that change the speed step by step depending on the load.

Interface of connection with the computer - IDE, SATA, USB, SAS, etc. Having mentioned USB, it is impossible not to say what an external hard disk is.

With all the advantages of hard drives, they have long been internal devices of computers, located in the system unit. Modernization of the parking zone (magnetic latch of the carriage of the heads, mechanical locking) made it possible to make a hard disk portable. This is the same hard drive, but designed for more complex operating conditions. The case does not have open electronics blocks. Connects to the computer via USB or FireWire. The speed of rotation of the spindle is usually limited to 5400 rpm (reduction of power consumption).