Description The hard consists basically of one or more aluminum or glass disk, coated with ferromagnetic material in rapid rotation and two heads for each disk (one for side), which, during operation "fly" at a distance of a few tens of nanometers from the surface of the disk reading and writing data. The head is kept raised by 'air moved by the same rotation of the disks that can exceed 15,000 rpm, and currently the default values \u200b\u200bfor rotation are 5,400, 7,200, 10,000 and 15,000 rpm.
History
Pair of heads positioned at 'end of both arms moving reading, missing the record, are in contact with each' other. The 'hard drive was invented in 1956 by' IBM. The first prototype consisted of 50 discs with a diameter of 24 inches (60 cm) and could store about 5 megabytes of data. It was the size of a washing machine. The original name was fixed disk drive (HDD), the term hard disk drive (HDD) was born around 1970 to contrast with infants floppy disk (diskette). In 1963 IBM
always conceived the mechanism for lifting the head through the 'air. In 1973 IBM introduced the Model 3340 Winchester, named per analogia con il popolare modello di fucile ".30-30 Winchester" poiché era dotato di due dischi da 30 MB l’ uno; questo nome entrò nell’ uso comune come sinonimo di disco rigido perché questo modello fu il predecessore di tutti i dischi rigidi moderni.
Il primo modello per personal computer fu il Seagate ST-506 prodotto da Seagate Technology nel 1980, aveva una capacità di 5 MB, diametro di 5,25 pollici ed era dotato di motore passo-passo per il movimento delle testine (il controllo voice coil arriverà solo qualche anno dopo). Questo modello equipaggiava i personal computer AT&T con processore 286 prodotti negli stabilimenti Olivetti di Scarmagno, in seguito alla company's collaboration with the American multinational Ivrea. At the same time, the company OPE (Olivetti Peripheral Equipment), a subsidiary of Olivetti, provided the hard disks for computers M24, this company was historically the 'unique in Europe to engage in the design, development and production of this type of device.
Performance Characteristics
8 gigabyte hard drive disassembled into its component modern hard disks have capacities and performance vastly superior to those of the early models, but in the meantime because the speed and performance of random access memory (RAM and ROM) are significantly higher, their speed in reading and writing Data are still several orders of magnitude below the performance of RAM and solid state components that equips a computer. For this reason the hard drive is often the primary cause of slowing down a computer, especially if, due to a RAM lower than the virtual memory required by the programs running, the operating system is forced to carry a large number of swaps between the disk and main memory.
The main features of a hard drive are: the ability
access time
transfer rate
The capacity is usually expressed in gigabytes (GB). The manufacturers use decimal gigabytes, invece delle approssimazioni per potenze di due usate per la memoria. Questo significa che la capacità di un disco rigido è in realtà un poco più piccola di quella di un modulo di memoria con la stessa capacità, e lo scarto aumenta all’ aumentare delle dimensioni. Quando la capacità è espressa in GB, il fattore di correzione è di (1000/1024)3, pari a circa 0,93, per cui un disco rigido da 320 GB ha una capacità effettiva di circa 298 GiB. Attualmente (luglio 2009) i dischi rigidi si trovano in vendita con capacità fino a 1.5 TB. Alcune aziende accoppiano più dischi in un unico box per arrivare a capacità di 7,5 TB ma si tratta di un espediente, ad es: Lacie Big Disk, Maxtor Shared Storage, etc. The capacity can be increased by increasing the density with which information is stored on the plates that make up the 'drive, or using a higher number. The race to drive ever more capacious never stops, is currently the 'bigger is the Seagate drives, "7200.12", 1.5 TB. In parallel down the cost per GB, the price of this unit is less than € 150.00.
The access time is the most important variable in determining the performance of a hard drive, knowing the model can easily be traced to the technical data of 'units, including the access time, unfortunately many computer manufacturers do not mention this figure, and sometimes even the make or model. This is the average time required for a given, a resident of a random point on the disc, can be found. This time depends on the speed of head move on the track where the data resides and the speed of rotation of the disk, the faster and shorter the time it takes to wipe data under the head if this had not arrived in time on the data during the previous rotation (rotational latency). The producers therefore seek to achieve more and more read heads (which can move more quickly because they have less inertia) and disks that spin faster. The typical access time for a 7200 rpm hard drive is about 9 milliseconds. For a 15,000-rpm is less than 4 ms.
The transfer rate is the amount of data supplied by ' hard disk at a given time (usually takes 1 second as a reference). Use discs that rotate faster or increase the storage density leads to a direct improvement of the transfer rate. It should be noted that the transfer rate decreases in proportion to the number of discontinuities in the areas that make up the file search (see fragmentation).
addition to the three views above, to a lesser extent other characteristics affect the performance a hard disk. These include:
the memory buffer
the speed of 'interface
The buffer cache is a small (typically a few megabytes) on-board hard disk, which is responsible for storing the last data read or written by disc. In the case where a program repeatedly read the same information, they can be found in the buffer rather than disk. Since the buffer is a non-mechanical and electronic component, the transfer rate is much higher, over time, the capacity of this memory has been gaining increasing, now 32 MB in size are not unusual.
L 'link interface between the hard disk and motherboard (or, more specifically, the controller) can affect performance because it specifies the maximum speed at which information can be transferred to or from the disk. The modern interfaces such as ATA133, Serial ATA or SCSI can transfer hundreds of megabytes per second, far more than any single hard drive can do, and then the 'interface is not usually a limiting factor. The speech may change in the 'use of multiple disks in RAID configuration, in which case it is important to use' interface as fast as possible, such as the Fibre Channel 2 Gb / s.
