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Hard Disk Fundamentals

Hard Disk Fundamentals
By: Muthu Senthil Kumar (mskumar@tataelxsi.co.in / mskumar86@myway.com)

From hard drive:

HDD, the magnetic device is used to store electronic copies of data in the form of 0 and 1. specific drivers are used to retrieve the data back in a specified format. Magnetic hard disks are used from 1956. That day, the size of hard drives is very huge for a small amount of storage and it also takes more time to store and retrieve. But today, we use very compact, high capacity hard drives in high latency for our systems.

physical representation of hard disk:

User data / information are stored on media surface of a disc. The support is a specially coated surface. Each surface Support is divided into tracks and sectors. These areas are often called "blocks." The tracks are often referred to as the cylinders. The trail separations sector of the disk drive are displayed below. The Cylinder, Head, Sector (CHS) provides a physical location.

Logical representation of HDD:

The hard drive using circular platters to store data. Each platter has two surfaces. Both sides of the bracket are used to store information. If each surface has 4 tracks and 4 sectors means that there would be 32 sectors or blocks. Each surface requires a "head" to read / write information. The surfaces are often referred to as the "head". A cylinder head is the area that can read or write without being positioned on another track.

Take a hard disk has two surfaces and head, four sectors / blocks, then the logical representation of this record will be like that in Figure 3. In this figure, the two leaders on this disc represented as 0 and 1. The four-cylinder / tracks and sectors are represented by 0-3. So for each surface has 16 logical sectors / blocks is appointed as a logical block addressing (LBA).

The host and the file system using the LBA only for the functioning of the disc hard as reading, writing data, research and search etc., but for the leaders and the media channels hard disk driver to convert the LBA the CHS (Cylinder, Head, Sector).

Reading and writing to disk:

Hard Disk Drive is a device for storing digital data that reads and writes data via changes in magnetization of a magnetic storage disk. This includes one or more storage media accessible to chance rotary or disks. In a magnetic disk drive, data is encoded as bits of information using magnetic field reversals grouped securities of the surface magnetic hard disks rotating. It also includes a sensor supported by a hydrodynamic bearing which flies above each magnetic disc. The sensor head supported by a control arm is used to read data from or write data on discs. Hard drives are an essential in most modern computing and data handling systems.

Hard drives are commonly used to store relatively large quantities data into the computer systems of today as the desktop. If the disk capacity is more, the computer can store and access more data. In a computer, a floppy disk drive is connected to the central processing unit (CPU) by means of the bus system. architectures have a computer motherboard that includes a CPU and the bus system to which various peripheral devices including a floppy disk drive, are connected.

In a hard disk, data signals are read and written from a rotating disk by a head, which is moved substantially relative to the disk. The head assembly facilitates the reading and writing information on a surface of a rotating magnetic disk. All interconnection includes a plurality of transmission, such as son or traces, transmission of data to and from the whole head. The mounting positions of the suspension head assembly at a substantially constant distance from the surface displacement of the rotating disc. When power Power is cut at the end of the use of a computer, a control voltage of a spindle motor also stops for the speed hard disk rotated by the spindle motor is gradually reduced. At this point, the magnetic head in the state to fly above the disk by the air flow down on the surface of the disk.

The servo system generally performs two distinct functions:
• seek to control
• Next Track

The search function command comprises a controlled manner to move the control arm so that the head the sensor is moved from an initial position to a position leading to the target. The read / write is usually a part of or attached to a larger body that flies over the disk and is generally regarded as a cursor. The cursor has a lower surface called air cushion surface. The surface air cushion generally includes one or more rails which are typically generate a positive air pressure

The host sends the READ command on the hard disk, it is transferred to logic physical hard disk and then send the data block specified read. At the time of writing in the memory, the host sends the WRITE command to the hard drive. After receiving the acknowledgment, data is sent via bus to write to the specified block.

HDD Interface:

A common border between two or more functional units, defined by specific attributes, such as functional characteristics (phases, states, protocol), characteristics common physical interconnection (cable, plugs), and the signal characteristics (polarity, voltage range, timing). This is what called the interface. There are two main ways of hard disk interface with the host. They are

ATA (Advanced Technology Attachment)

PATA (Parallel Advanced Technology Attachment)

SATA (Serial Advanced Technology Attachment)
SCSI (Small Computer System Interface)

ATA (PATA):
ATA is a common interface used in many personal computers before the emergence of SATA (Serial Advanced Technology Attachment). Version original ATA is a parallel. Then after the lifting of SATA, it is usually called PATA (Parallel Advanced Technology Attachment). It is the least expensive interfaces used in the system in the old days. PATA can support data transfer up to 133 Mb / s. Today SATA replaces this PATA in all areas. But UDMA133 recent version is used in certain sub-systems depends on the customer requirement.

SATA:
Serial Advanced Technology Attachment is commonly called SATA. It is the hard disk interface very common in all home systems. SATA Port allows device to connect to it. The main disadvantage of this is, it does not support older systems, without the use of additional components

SCSI:
It is abbreviated as Small Computer System Interface. SCSI is widely used in servers, and more in industrial applications that uses at home. It is the storage component famous under-utilized in all computer interfaces for small and medium level. A mechanism called "Cable sharing" used here. It can support data transfer rates up to 320 Mb / s.

HDD - Enterprise Information:

In the enterprise level, companies differentiate themselves by using their hard drives spindle revolution per minute (RPM) as the 4,200 RPM drives hard drives 5400 rpm, 7200 rpm hard drives, hard drives 10000 rpm, 15,000 RPM hard drives. These are all major manufacturers and businesses to work with hard disks and marketing.

Audavi, Dane-Elec Memory, Dataslide, DTS, Dynamic Network Factory, EDGE technology Excelstor Tech,, EZQuest Fantom Drives, Training Freecom Technologies, Fujitsu, Hitachi, Imation, I / Omagic, Iomega, LaCie, Maxell, Miltope, NEC Technologies Olix,, PNY Technologies, ProStor Systems, Quantum, Samsung Electronics, SDK, Seagate, Shining Technology, Sony, Soyo, Toshiba, Verbatim, Western Digital

Hard drive failures:

drive failure drive is one of the most frustrating experiences with computers. The inability to read data from the hard drive can make a computer unusable. Even if the OS can work, the data may be inaccessible or damaged. The only way to recover from such an omission is generally restore data from a backup on a new disk with all software installed from scratch. If no backup is available, data is lost or will cost a lot for collection services to recover.
disk failures common

The most common failure for a hard drive is called a head crash. A head crash is a case where the drive head manages to touch a plateau. When this occurs, the magnetic media will be burned off the shelf by the head and make the data and the head drive unusable. There own no recovery of such failure.

Another common failure is of imperfections on the magnetic medium. Any time a sector on the disk fails to keep proper alignment will cause magnetic data inaccessible.

Mobile systems tend to be subject to serving dishes that burst. This was due to the fact that the hard disk platters are more glass and was sensitive to shocks.

MTBF:

For consumers to have a good idea of the life of a hard disk, a disk was measured by MTBF. This term is Mean Time Between Failure and is used to represent the length of time that 50 percent of readers who fail before and 50 percent would fail after. It is used to give an idea to a buyer on the average amount of time the system must work for. The "Mean Time Between Failures (MTBF) for hard drives were mounted fairly steadily from about 200,000 hours in 1990 to nearly 1.2 million hours today.

Recovery software:

At the time of hard disk failure, the user wants to retrieve all data from that hard drive failure. More companies offer the software disk recovery disk data recovery. Some of them would be free too.

About the Author

Muthu Senthil Kumar - Patent Engineer, Zoho Corporation, Vijaya Nagar, Velachery, Chennai - 600042, Tamil Nadu, India - Mail: muthusenthilkumar.m@zohocorp.com / mskumar86@myway.com - Ph: +91 9003242037

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