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 platter2.Spindle and spindle motor3.Read/write

heads4.Head

actuators5.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, 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 actuator2. 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.