Hard Disk Drives

Hard Disk:
A Hard disk is a secondary and permanent data storage device that is placed in the system. Now a days 2TB (2000GB) Hard disk also avalable.
A Hard disk consists of several circular platters. Each platter has read/write heads on both the sides. The platters are divided into concentric circles called as tracks, and each track is divided into smaller units called sectors. The read/write head examines and records data in these sectors. the identically aligend tracks on each side of every platter together make up cylinder.

TYPES OF HARD DISKS:
1. Standard Drives ( IDE/PATA )
2. Serial ATA ( SATA )
3. SCSI Hard Disk Drive
4. External Hard Disk Drives ( USB 2.0/Firewire )
5. Wireless Hard Disk Dirves

IDE ( Integrated Drive Electronics ):
The ATA transfers data between the hard disk and system using 16 bits with speeds of up to 100MB/133MB per second. you can connect two Hard Disks to a single controller on the system. You must set the Hard Disk to master or slave using the jumpers on the hard dis, so that the system can identify the required hard disk. This hard disk uses a 40-pin connector to connect to the system.
Also know as IDE,EIDE,PATA. ATA interface that transferred data at speeds 25MB per sec used programmed input output (PIO) technology to transfer data. ATA interfaces transferred data at 25MB per sec or higher used the ultra Direct Memory Acces (UDMA) method to transfer data. In the PIO method, the CPU controls the transfer of data from the hard disk whereas the chipset controls the transfer of data in the UDMA method

SATA ( Serial AT Attachment ):
Serial ATA transfers data using 1 bit with the speed of upto 600MB per sec but External SATA is capable of 1.5 Gbps. SATA hard disk uses a smaller 7-wire cable to connect to the system. this cable can have a maximum length of 1 meter. The power cable of a SATA hard disk is smaller tham the MOLEX connector used in ATA hard disks.
You can connect only one Serial ATA hard disk as a master or slave. You can connect more than one hard disk by connecting them to different SATA controllers on the motherboard using separate cables.

SCSI ( Small Computer Systems Interface ):
SCSI HDD is typically used in network server which includes lot of processing. SCSI is a high speed interface that enables you to connect up to 15 devices on a single port. SCSI is used with RAID (Redundant Array of Inexpensive Disk), whare two or more disks are combined together to form a single hard disk. RAID allows to access data quickly and prevents loss of data in case of a hard disk crash.

External Hard Disk Drives ( USB, Firewire )
External HDD can be connected using USB2 and Firewire interfaces. External HDD also supports high-speed data transfer. External Hard disks that uses interfaces consumes the required power from the port through which they are connected like USB or Firewire.

Wireless HDD:
Wireless Hard Disk Drives are small and light in Weight. They use 802.11g standard for communication. WL HDD requires external power supply.It is a Wi-Fi hard disk. Data transfer rate is 54 mbps.