The Hard Drive

1. The Hard Drive

2. What is a Hard Drive? A hard drive is something that is used to store data longer than the next time the computer is turned off.

3. Definition of a Hard Disk A hard disk contains rigid, disk-shaped platters, usually constructed of aluminum or glass.

4. Hard Drive Advancements The maximum amount of storage has gone up. The price has drastically come down.

5. What is Areal Density? This is a term used as a technology growth rate indicator for hard drives. Areal density is a measure that states how many bits per inch are present on the disk. As time goes on, more bits per inch are becoming possible.

6. Hard Disk Drive Operation Track � One of the many concentric circles that holds data on a disk surface. Consists of a single line of magnetic flux changes and is divided into some number of 512-byte pieces (sectors) Sector � A section of one track defined with identification markings and an identification number.

7. Continued Cylinder � The set of tracks on a disk that are on each side of all the disk platters in a stack and are the same distance from the center of the disk. The total number of tracks can be read without moving the heads. Rack � The mechanism that the read/write heads are mounted on. Platters � A disk contained in a hard disk drive. Most hard drives have two or more platters, each with data recorded on both sides.

8. Random info The disc tracks are too large to make it efficient to store large files, so it is divided up into smaller sectors. The platters have a cushion of air, so they are �floating� in the hard drive.

9. Disc Formatting The two types of formatting are: �������� Physical or low-level formatting �������� Logical or high-level formatting Unlike a floppy, hard drives are not formatted both ways at the same time.

10. What are the basic components of a hard drive? �������� Disk platters �������� Read/write heads �������� Head actuator mechanisms �������� Spindle motor �������� Logic board �������� Cables and connectors �������� Configuration items (such as jumpers and switches)

11. The hard disk platters �Currently, the 3 � inch drives are the most popular for desktop and some portable systems �Max. number of platters in a 3 � inch drive is 11 �Platters traditionally made from aluminum alloy. The desire for higher density has led to the use of platters made of glass (glass-ceramic composite). Glass platters offer greater rigidity and more stable thermally

12. Ways magnetic info is stored Two most popular types of magnetic media: 1.����� Oxide media 2.����� Thin-film media

13. Oxide media Made of various compounds, oxide being the primary active ingredient. It is put on the disk like syrup, coating the entire disk. The coating is approx. 30 millionths of an inch and is made smooth. The platters appear to look brownish or amber. Very sensitive to head-crash during movement of operation. Very few drives use this technology anymore.

14. Thin-film media This is thinner, harder, and more perfectly formed than oxide media. The coating is put on the platter using a electroplating mechanism. These look like silver surfaces of mirrors. There is a great chance of survival of the thin-film media coming into contact with the heads at high speed. Virtually unscratchable!

15. Read/Write Heads There is one head for each side of every platter. They all move in unison.

16. Head Actuator Mechanisms The thing that moves the Read/Write heads around and puts them into position.

17. Air filters Nearly all hard disk drives have two air filters. One of them (recirculating filter) filters small particles scraped off the platters during takeoffs and landings. The other (breather filter) allows for pressure equalization. This is important because if the pressure is not right, the heads won�t float.

18. Drive acclimation Drives are very sensitive to temperature. If the drive has been very cold, let it acclimate before powering on. Humidity is of concern as well.

19. What is the spindle motor? The spindle motor is the motor that spins the platters. They are connected directly to the drive.

20. Logic Boards The logic boards are mounted on the hard drive. They contain the electronics that control the drive�s spindle and head actuator systems and that present data to the controller in some agreed-upon form.

21. Cables and Connectors Hard disk drives typically have several connectors for interfacing to the computer, receiving power, and sometimes grounding to the system chassis. Most drives have at least these three types of connectors: 1.����� Interface connectors 2.����� Power connectors 3.����� Optional ground connector

22. The Speed of the Drive Average Seek Time: Measured in milliseconds, is the average amount of time it takes to move the heads from one cylinder to another cylinder a random distance. A slightly different measurement = Average Access Time. This involves latency. Latency is the average time that it takes for a sector to be available after the heads have reached a track. Latency is a factor in the disk read and write performance.

23. Continued Transfer Rate: This is probably more important overall to system performance than any other statistic. It is the rate at which the drive and the controller can send data to the system. The transfer rate depends primarily on the drive�s head disk assembly and secondarily on the controller. Interleaving � The ordering of sectors so they are not sequential, enabling a slow controller to keep up without missing the next sector.