Hard Drive (HD)

The HDD was invented by IBM in 1956 as the RAMAC with a size of 24 inches, 50 trays and a capacity of 5 MB. Current capabilities beyond the terabyte sizes have also evolved since the PC desktop and servers use sizes of 3.5 inches (2.5 inches for Notebook and Netbook)

There are four types of interfaces currently: IDE - ATA, S-ATA, SCSI and SAS (the two latter are used exclusively in servers). Other types used in the first IBM PC XT as MFM and RLL disappeared. The SSD use the S-ATA, but the recording technology used more turntables covered with a magnetic product like memory flash (such as USB drives and memory cards used by cameras)..

Constitution and functioning.

A series of aluminum plates on a rotating axis using a motor. These trays are covered with elements electromagnetic retain data when the drive is no longer power. Each tray uses a read / write controlled a second engine. It moves all the heads (one per tray) simultaneously.

To supplement the data collected by headers are transferred to a controller that formats the data and controls the different motors. It serves as an interface with the motherboard via a cable.

Characteristics.

• External size. Desktop PCs and servers use 3.5 inches disks. Laptops use 2.5 inches disk with lower consumption.
• Access Time is average time to move the read / write on a platter. It depends mainly on the characteristics of the engine.
• Rotational speed, Expressed in RPM is related to the speed the main engine. The higher, the higher the rate is tansfert  high but is also related to the interface. Most hard disks  current run at 7200, a few models for the cheapest laptops work in 5400. Those specific servers and networks come to 10,000 even 15,000. They use connections in Ultra 320 SCSI or SAS (Serial Attached SCSI) that the only fool to allow such transfer rates.
• The number plate. In practice, the higher it is, the more the disc is  fast for the same capacity. Each magnetic plate is cut into  circular tracks. The size of these tracks depends on capacity by  plateau.

The Formatting Low (Physical) cut each track sectors 512 bytes (The standard size but can vary from one model to another). When formatting, Windows will create on each sector clusters whose size depends on the type of partition used (FAT (VFAT) - FAT32 - NTFS...) But also in different versions of FAT capacity of each tray. The sector Boot is used to allow the Windows startup and choosing the OS multi-boot.

The capacity of a hard disk can thus be deduced from the formula below:

Net Capacity = number of sectors * capacity of sectors * * number of cylinder heads.

Can I install any hard drive on your PC?

Not really. The first thing is to determine the type that your computer supports (IDE for first computers, ATA, SATA or SCSI). This is related to the type of controller installed on the motherboard, current models incorporate a SATA2 and PATA Controller. SCSI connections use most often controller implemented on a card attached.

The second limitation is related to the BIOS and operating system installed, they are limits capacity for old PC to use disc too large (eg greater than 160 GB) ..

Hard drive failure.

Various problems are associated with hard drives. We can distinguish hardware faults (Crash disc) As a head designer trays (shock), engines or controllers fail, possibly bad clusters. A BIOS Setup option (SMART) prevents forward for some of these failures. Level software, different problems can be solved by using the DOS commands or Recovery Console. Among these, we find CHKDSK to detect and mark bad sectors, but also the various NTLDR errors in NTFS partitions.

Types of hard disk connections: Raid