Hard disk drive a dialectical dialogue
Hard disk contains rigid, disk shaped platters usually constructed of aluminum or glass. It’s a sealed unit that PC uses for nonvolatile data storage.Hard drive is used to store crucial programming and data, As a result when the hard disk fails, the consequences are usually very serious. The platters of hard disk are hard in texture hence the name harddisk.Moreover the platters are not removable.
3 ½”, SATA drives are most commonplace in desktop systems. The basic physical construction of a hard disk drive consists of spinning disks with heads that move over the disks and store data in tracks and sectors. The heads read and write data in concentric rings called tracks, which are divided in to segments called sectors, which typically store 512 bytes each.
Most drives have two or three platters, resulting in four or six sides, but some disks have from 1 to 12 platters and 24 sides with 24 heads to read them. The heads fitted on actuator move radially across the disk in unison. Most standard-issue drives found in PCs today spin at 7,200 rpm, with high performance models spinning at 10,000 rpm mostly being servers. High rotational speeds combined with fast head-positioning mechanism and more sectors per track are what make one hard disk faster overall than another.
The heads do rest on platters when powered off. When powered on heads move to the inner most cylinder, where they land on platter surface, slide on platter as they spin up, until a very thin cushion of air builds up between the heads and the platter surface, causing the heads to lift of and remain suspended a short distance above or below the platter. Because few companies repair the hard disk assemblies (HDAs).Repair or replacement of the parts inside a sealed HAD can be expensive. Every hard disk ever made eventually fails. The only questions are when the failure will occur and whether your data is backed up.Hard disks are one of the most fragile components of a PC.Manufacturers void guaranty if the seal is broken. Most of the modern hard disks are sold preformatted and advertise only the formatted capacity. That means each sector on disk typically occupies up to 571 bytes of the disk, of which only 512 bytes available for the storage of the user data .That is the usable space for data on each track is about 15% less than its total unformatted capacity.
Preparing a hard disk driver for data storage involves three steps namely low level formatting, which is done at factory. Disk partitioning for any multiple operating and/or file systems on each directory and finally high level formatting. All modern hard disks use zoned recording to enable the capacity of disk to 20-50% more.
Every hard disk must have at least one partition on it and can have up to four partitions. Each of which can support NTFS or different file systems. During high level format, the operating system writes the structures necessary for managing files and data on the disk. High level formatting is not really the physical formatting of the drive, but rather the creation of table of contents for the disk. In low level formatting which is the real physical formatting process, tracks and sectors are written on the disk, A FORMAT DOS command performs high level formatting on the disk.
The basic components of a typical hard disk drive are disk platters, read/write heads, head actuator mechanism, spindle motor (inside platter hub).These are situated in a sealed assembly called Hard disk assembly (HDA).Other parts are external to the drives HAD such as the logic boards, bezel, and other configuration or mounting hardware, can be disassembled form the drive.
Virtually all the modern drives use glass or glass ceramic platters instead of aluminum/magnesium alloy platters. Platters are covered with a thin layer of a magnetically retentive substance, called medium, on which magnetic information is stored. Old days since 1955 oxide media remained popular. Modern platters are sputtered with thin film medium, Anti ferromagnetic alloy coupled (AFC) media being the most recent development. All hard disk drives being manufactured today use voice coil actuators to achieve the accuracy necessary. In typical hard disk drive’s voice coil system, the electromagnetic coil is attached to end of head track and placed near a stationary magnet. No physical contact occurs between the coils and the magnet, instead the coil moves by pure magnetic force, Use a feedback signal from the drive to accurately determine the head positions and adjust them if necessary. The positioning system often called a closed loop feedback mechanism or servo controlled sytem.Virtully all voice coil sytems today have rotary actuator systems. All servo mechanism relies on special information that is written to the disk when it is manufactured. This information is usually in the form of special code called gray code, a special binary notational system.
Most drive today use an embedded servo to control the positioning system. Embedded servo design writes the servo information before the start of each sector. Hard disk assemblies are manufactured in clean room environment. The equipment for clean room environment is expensive which makes the repair/opening up of hard disk for repair companies costlier. There is no program written to perk or retract heads, as was necessary with early hard disk designs. In the event of a power outage, the heads park themselves automatically.
The HDA in hard disk drive is sealed but not air tight. The HDA is vented through a barometric or breather filter element that enables pressure equalization (breathing) between inside and outside of the drive. For this reason most hard drives are rated by the drives manufacturer to run in a specific range of altitudes, usually form 1,000 feet’s below to 10,000 feet’s above sea level.Infact some hard drives are not rated to exceed 7,000 feet while operating because the air pressure would be too low inside the drive to float the heads properly. You must place the hard disk drive that has been placed in colder than normal environment into its normal operating environment for a specified amount of time to allow it to acclimate before you power it on.
The logic boards contain the electronics that control the drives spindle and head actuator systems and present data to the controller in some agreed upon form. Many disk drive failures occur in the logic board, not in the mechanical assembly. Most of the time the boards are fairly easy to change with nothing more than a screw driver. Merely removing and reinstalling a few screws as well as unplugging and reconnecting a cable or two is all that is required to remove and replace a typical logic board.
The power is supplied by the larger 4-pin peripheral power connector found on all PC power supplies. Most hard disks have both 5 and 12 volts power. In most cases the 12 volts power run the spindle motor and head actuator, and 5volts power run the circuitary.Other than power connector hard disk contain interface connector and ground connector to the system’s chassis.
If the motherboard ROM BIOS dates before 1998 and is limited to8.4GB or dates before 2002 and is limited to 137GB, you have to install a larger drive. First contact your motherboard manufacturer to see whether an update is available. Virtually all motherboards incorporate a flash Bromwich allows easy updates via a utility program.
By comparison the interface rate merely indicates how quickly data can move between the motherboard and the buffer on the drive. The rotational speed of the drive has the biggest effect on the drives true transfer speed, be sure to check the true media transfer rates of any drive you are comparing.
Average seek time usually measured in milliseconds is the average amount of time it takes to move the heads from one cylinder to another a random distance away. Latency is the average time it takes for the sector to be available after the heads have reached a track. A measurement of drives average access time is the sum of its average seeks time plus latency.
When an application program wants to read data from a hard drive, A cash program such as SMARTDRV (DOS) and VCACHE (windows) intercepts the read request, passes the read request to the hard drive controller in the usual way, saves the data read form the disk in it’s cache memory buffer, and the passes the data back to the application program.Nowdays some 31/2” hard disk drives can have up to 16MB of cache memory built right in!
When you shop for a drive you might notice a statistics called the mean time between failures (MTBF) described in the drives specifications.MTBF figures usually range from 3, 00,000 to 10, 00,000 hours or more. Self monitoring, analysis and reporting technology (S.M.A.R.T) is an industry standard providing failure prediction for hard disk drives. When S.M.A.R.T is enabled for a given drive, the drive monitors predetermined attributes that are susceptible to or indicative of drive degradation. Based on changes in the monitored attributes, a failure prediction can be made. If a failure deemed likely to occur S.M.A.R.Tmakes a status report available so that the system BIOS or driver software can notify the user of the impending problems perhaps enabling the user to backup the data on the drive before any real problem occur. If you connect the new and existing (failing) drive to the same system. You might be able to copy the entire contents of the existing drive to new one. Saving you from having to install or reload all the applications and data from your backup. Because standard copy commands or drag-and-drop methods don’t copy system files, hidden files or the files that are open, to copy an entire drive successfully and have the destination copy remain bootable you need a special application such as Symantec Norton ghost or acronis true image
