power supply

The power supply unit of system mostly found in the top corner of the system case accepts the AC ( Alternating current ) from the power socket in the wall. It then converts the AC to DC ( Direct current ) for the system. Now a days power supplies are available in the range of 250W to 400W.

Types of power supply:
A power supply is a system which provides power to the circuit or the devices connected to it. Power supply converts the AC to DC voltage. Maney units of the computerrequir DC power. The two types of power supplies are Linear power supply and switch mode power supply.

Linear Power Supply-
Transforms incoming voltage to a lower voltage using transformers. A diode circuit is used to rectify the AC voltage to pulsating DC. the
capacitor filter is then used to provide DC voltage with low ripples. Finally,linear regulator is used to reduce the voltage to a desired level. Linear power supply is bulky but has very low noise.
Switch Mode Power Supply -
Uses high switching frequency. It is compact and can deliver very high power. It is used as DC to DC converter in which power switches, power connectors and power supply fan.

Power Connectors:
The power supply unit provides current to the motherboard, hard disk drive, floppy disk drive and various other components of a system using the power connectors carrying small amount of power are called signal connectors. There are 5 types of connectors.

1. AT power connectors
2. ATX power connectors
3. Standard peripheral power connectors ( Molex )
4. Floppy Drive power connectors ( Mini/Berg )
5. 2/3 Pin Mini plug type connectors

AT Power connectors -

There are two 6 wire connectors named P8 and P9 which are to be connected to the motherboard with black wires inside. The PC/XT, AT, Baby AT and LPX form factors of the power supply use a pair of 6 wire connectors, called as AT style connectors to connect the power supply to the motherboard.

ATX Power Connector -

This is a 20 pin connector with 6 types of voltage coming out of it. The ATX Style power connectors for the ATX/NLX from factors use the ATX Style power connectors. This style has a single 20-pin connector.

Standard peripheral power connectors ( Molex ) -

The disk drive power connectors use 4 wire connectors. The 4 wire connectors are available in large and small size connectors. The hard disk drive, CD/DVD drives use larger size connectors, commonly called as Molex.

Floppy Drive Power Connectors ( Mini/Berg ) -
The 3.5-inch floppy disk drive use smaller size connectors, called as mini-plug.

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.