GENERAL INFORMATION Invented in 1950's on mainframe computers with 20 inches diameter with only few megabytes of data. Originally called 'Fixed Disc' or 'Winchester Drive‘ (code name for IBM product). Named as hard drive to differentiate it from floppy disc. Current hard drive = changes in size and capacity, but basic technology is still the same.

2 ways to measure the performance of a hard disk: 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. 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. * The other important parameter is the capacity of the drive, which is the number of bytes it can hold.

Hard Disc is the most popular storage device used to store data in most computers. Hard Disc Drive (HDD) is the mechanism that controls positioning, reading and writing data of hard disc, which provide the largest amount of data storage for PC. Capacity is usually quoted in gigabytes.

COMPONENTS : 1.Disc platter 2.Spindle and spindle motor 3.Read/write heads 4.Head actuators 5.Connectors and jumpers

Basically, HD consists of flat disc called platter, coated on both sides with a special magnetic media material designed to store data. Platters are mounted by cutting a hole in the center and stacking them onto a spindle. The platters rotate at high speed, driven by a special spindle motor connected to the spindle. IN GENERAL :

R/W heads are mounted onto sliders and used to record data onto disc or read data from it. Sliders are mounted onto arms, all of which are mechanically connected into a single assembly and positioned over the surface of the disc by a device called an actuator.

Platter Platter size is the form factor. Disc sometimes referred to by a size spec. e.g. 3.5 inch hard disc First PC used hard disc with size of 5.25 inch. Common size for hard disc platter is 3.5 inch. Laptop drives are usually smaller, 2.5 in diameter or less (1.8 inch and even 1.0 inch platter are becoming more common) and PC are 3.5 inch.

PC usually have 1 to 5 platters. Can also be called as 'disc', or more commonly called as 'Primary Unit'. Is the storage media for the disc drive. Primarily made from aluminium alloys and glass. Most of top manufacturers use glass composite materials (e.g. Seagate, Toshiba and Maxtor).

Spindle and Spindle Motor Disc platter are mounted to a spindle separated by disc spacer that keeps the platters evenly spaced. The space is also used by the R/W heads to access the top of disc and bottom of the before disc. It rotates in the speeds of : 3600 rmp, 4800, 5400, 7200, and rmp.

Motor that rotates the spindle and disc mounted on it is called the spindle motor (spindle shaft). Many drive failures are actually failures with the spindle motor. All HD spindle motors are configured for direct connection; no belts or gears that are used to connect them to the HD platter spindle.

Head Each side of the platter allows to store data. * If there are 2 platters, then there will be 4 read/write head (1 to read and write data to the top side, another 1 for the bottom side). These heads are connected to the same actuator mechanism, moves the heads in unison in and out, from the spindle, to the edge of the platter. Heads do not make contact with the media (or disc), but float over the surface of the disc, not touching the platter.

Each platter has 2 heads mounted onto sliders and used to record information onto disc or read information from it. Head crash = heads contact the surface of the disc while it is at operational speed, causing loss of data, damage to the heads, damage to the surface of the disc.

Head Arms Sliders are mounted onto arms which are thin pieces of metal, usually in triangular shape. Arms are controlled using actuator, that positions the arms to the appropriated track on the disc.

Head Actuator R/W heads are moved into position by the head actuator. This mechanism is used to extend and retract the heads so that data can be read from or written to the disc platter. Categorized into 2 : 1. stepper motor actuator 2. voice coil actuator

Connectors and Jumpers In general, there are 3 types of connectors (data and power are common and the optional connector is not shown in most disc drives). Data connector (interface connector) carries both data and commanded signal from controller and CPU to and from the disc drive. Power connector is the standard power connector available from the PC's power supply.

Logic & other circuitry uses 5V; spindle motor and actuator use 12V power. Jumper: used to configure the drives as a master or slaves on a shared interface, as well as other configuration settings.

Tracks and Sectors Each platter has its information recorded in concentric circles called tracks. Each track broken down into smaller pieces called sectors (each holds 256 or 512 bytes of information). Larger outer tracks hold more sectors than the smaller inner ones. All information stored on a hard disc is recorded in tracks.

Tracks are numbered from zero, starting at the outside of the platter. Sectors are not read individually on most PCs, but grouped together into continuous chunks called clusters. Since there are corresponding tracks on the top and bottom of each disc in the stack, the HDD controller organizes them into cylinders.

HARD DRIVE FORMATTING Formatting a disk for use by an operating system and its applications typically involves three different processes.