GENERAL INFORMATION Invented in 1950s on mainframe computers

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: 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 - 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. * 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

IN GENERAL : • 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.

• 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, 10 000 and 15 000 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 5 V; spindle motor and actuator use 12 V 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.