HardDisk

INTRODUCTION:-

The hard disk drive or hard drive is the main location where all data is stored. Most hard disk drives consist of spinning platters of aluminum, glass or ceramic that are coated with a magnetic media.

A single hard disk usually consists of several platters. Each platter requires two read/write heads, one for each side. All the read/write heads are attached to a single access arm so that they cannot move independently. Each platter has the same number of tracks, and a track location that cuts across all platters is called a cylinder. For example, a typical 84mb hard disk for a PC might have two platters       (four sides) and 1,053 cylinders.

COMPONENTS OF HARD DISK DRIVE:

Ø Platters

Ø Recording Media

Ø Read / Write Head

Ø Head Actuator Mechanism

Ø Air Filters

Ø Spindle Motor

Ø Logic Board

COMPONENTS OF HARD DISK

Platters: –

Round disks that are made up of metal or glass. Glass platters are preferred as shape of glass does not change when hard disk heats up

Recording Media:–

Made up of a magnetic material such as iron oxide and data is stored in this layer.

Read / Write Head: –

 Used to read and write the data on the hard disk. While the disk is reading or writing data to the disk the head does not touch the disk

Head Actuator Mechanism: –

Moves the read/write head from center of the platter to the edge of the platter

Air Filters: –

Cleans the air circulating in the hard disk

Hard Disk Temperature Acclimation:–

 Time that hard disk must not be used after it is transported from a place having cold climate to a place having warm climate. Air vents in hard disk that are used for equalizing pressure in hard disk

Spindle Motor: –

Spins the hard disk platters. They have to spin for many continuous hours without causing a lot of vibrations

Logic Board: –          

Controls the hard disk and stores data on hard disk platters

Cables and Connectors:–

Attached to the back of the hard disk

Configuration Items: –

Sets the hard disk using jumpers

Faceplate: –

 Front plastic covering of the hard disk. Latest hard disks do not have a bezel

WORKING OF HARD DISK:-

The Hard disk drive has four main components. The head actuator controls the head arm, which reads the information off of the disk platter. The chassis encases and holds all the hard disk drive components.

 Working of Hard Disk

Platter - The actual fixed disk within the hard disk drive. There can be several platters within the hard drive

Heads - Each side of a platter

Tracks - Large sections that completely circle the platter

Sector - Section on the track

Cluster - Smallest unit of measurement that a hard drive will read

Cylinder - Tracks of the same diameter on each platter

Performance ofa Hard Disk

Ø Capacity

Ø RPM 

Ø Data rate

Ø Seek time

Ø Buffer 

Ø Transfer Speed

Capacity:-

typical hard drives are about 100GB they can go up to 1 TB the more information such as pictures, files, music and videos your going to store the more space your going to need.

RPM:-

        Rotation per minute The best is 15,000 rpm however you should consider buying a hard drive with a fast rotational speed of 7,200 revolutions per minute (rpm) or higher. You should expect to spend less for a slower 5,400-rpm hard drive.

Data rate:-

The data rate is the number of bytes per second that the drive can deliver to the CPU. Rates between 5 and 40 megabytes per second are common.

Seek time:-

The seek time is the amount of time between when the CPU requests a file and when the first byte of the file is sent to the CPU. Times between 10 and 20 milliseconds are common.

Buffer:-

        When a system requests data, a hard drive will not only fetch what is requested, but it will also load its buffer memory with extra information that the processor is likely to ask for next. While a 2MB buffer is good, that's plenty of room to keep the data flowing, I found that drives with 8MB performed is best! for disk-intensive tasks

Transfer Speed:-

I.             Internal Hard Drives

Parallel ATA 33, 66, 100, 133MB/s
Serial ATA 150-300MB/s 
SCSI 33-640MB/s

II.           External Hard Drives

Serial ATA 150-300MB/s
USB 12Mbps up to 480Mbps
Firewire 400Mbps up to 800Mbps
SCSI 33-640MB/s

Type OfHard Disk:-

·        Standard Devices

·        Serial ATA

·        SCSI

·        External

·        Wireless Hard Disk Drive

Standard Drives (IDE/PATA/EIDE) –

ATA transfers data between the hard disk and system using 16 bits with speeds of up to 100 MB/133MB per second. Uses Programmed Input Output (PIO) or Ultra direct Memory Access (UDMA) technology to transfer data. Maximum 4 HDDs can be connected.

IDE/PATA/EIDE CONNECTOR

We can connect up to hard disk through this cable using jumper settings.

IDE:  usually contains one controller and 40 pins where you can install up to only 2 devices a typical speed of an IDE drives is about 3/MBs.

EIDE:  supports data rates of between 4 and 16.6 MBps, about three to four times faster than the old IDE standard. In addition, it can support mass storage devices of up to 8.4 gigabytes.

PATA: Known also as IDE, supports one or two hard drives, a 16-bit interface and PIO modes 0, 1 and 2.

Serial Attachment (SATA) –

Transfers data using 1 bit with the speed of 600MB per second.Uses a smaller 7 wire cable to connect to the system. You can connect one SATA drive to a SATA controller on motherboard and there is no master/slave concept.

 Serial ATA connector

Small Computer Systems Interface (SCSI) Hard Disk Drives –

High-speed interface that enables you to connect up to 15 devices on a single port, it is used in server computers to connect more no of devices.

External Hard Disk Drives –

External hard disk are Connected using USB2 and Firewire Interfaces.

 External Hard Disk Connectors

Wireless Hard Disk: –

Requires external power supply DTR is 54 Mbps, supports wireless 802.g standard and provides interface RJ45 and USB 1.1

Hard drive maintenance:

DEFRAG A DOS and Windows utility that defragments your hard disk. In Windows 95, you run Defrag by selecting Start->Programs->Accessories->System Tools->Disk Defragmenter.

SCANDISK A DOS and Windows utility that finds different types of errors on hard disks and is able to correct some of them. In DOS, you run Scandisk by entering scandisk at the prompt and pressing the Enter key. In Windows 95, you can run Scandisk by selecting Start->Programs->Accessories->System Tools->Scandisk. 

Among other things, Scandisk checks the disk platters for defects and also looks for lost clusters that are sometimes created when a program aborts.

In Windows 2K/XP go to start>run>cmd and type CHKDSK from the command prompt

FILE SYSTEMS:-

·        FAT (File Allocation Table)

·        NTFS (New technology file system)

FAT (File Allocation Table):-

 A table that the operating system uses to locate files on a disk. Due to fragmentation, a file may be divided into many sections that are scattered around the disk. In DOS systems, FATs are stored in hidden files, called FAT files . 
The FAT system for older versions of Windows 95 is called VFAT, and the one for new versions of Windows 95 and Windows 98 is called FAT32. A new version of the file allocation table (FAT) available in Windows 95 OSR 2 and Windows 98. FAT32 increases the number of bits used to address clusters and also reduces the size of each cluster. The result is that it can support larger disks (up to 2 terabytes) and better storage efficiency (less slack space).

NTFS:-

New technology file system (NTFS)  use in Windows 2K/XP/NT environment for security support.

Formatting the Hard Disk:

Ø Erases all the contents of the drive 

Ø Creates the sectors, tracks and places the file system on the hard disk

Ø Format a hard disk after you install a new hard disk on the system or to erase all the contents on the disk

Two types:

•         Low Level Formatting

•         High Level Formatting

Low Level Formatting:

                    Low-level formatting is the process of outlining the positions of the tracks and sectors on the hard disk, and writing the control structures that define where the tracks and sectors.  the first time that a low-level format  (LLF)  is performed on a hard disk, the disk’s platter start out empty. If an LLF’s done on a disk with data on it already, the data is permanently erased.

High Level Formatting:

                        After low-level formatting is complete, we have a disk with tracks and sectors–but nothing written on them. High-level formatting is the process of writing the file system structures on the disk that let the disk be used for storing programs and data. If you are using DOS, for example, the DOS FORMAT command performs this work, writing such structures as the master boot record and file allocation tables to the disk. High-level formatting is done after the hard disk has been partitioned, even if only one partition is to be used.

   

Troubleshooting:

Problems that can occur are:

•         System does not Start

•         Hard Disk Drive contains bad sectors

•         Hard Disk Drive crashes

•         Hard Disk does not display the correct formatted size