THE MODERN DAY HARD DISK DRIVE

The HDD or hard disk drive is a hardware device used as the storage medium for the computer.  It is used to store data, information, programs, images, and various other files permanently.  This means that it stays on the disk after the computer is shut off, and can be accessed over and over, until or unless you decide to delete the files on the HDD.  The files are written and stored on individual platters that reside inside of the HDD case.  These platters are covered with a special magnetic material on both sides.  The platters of the HDD spin at very high speeds.  These speeds are measured in RPM (revolutions per minute - how many times an object spins in a complete revolution in one minute).  HDD's spin at thousands of revolutions per minute.  To store files on the HDD, the read/write heads, which are located on the actuator arm, send small magnetic charges onto the surface of the platter.  Look at the picture and diagram below from PC Guide to see a close up of the parts inside a hard drive.

CASE & MOUNTING HOLES (where the cover is attached to the case and also where the HDD is  securely attached to the HDD bay in the computer case.)

POWER CONNECTOR (where the power connector and cable attach to the power supply for powering the HDD.)

JUMPER PINS & JUMPER (for setting the MASTER, SLAVE, CABLE SELECT, SINGLE , etc. settings for the hard drive.)

INTERFACE CONNECTOR .  (where the HDD connects to the motherboard or card controller with a flat ribbon cable.) In the picture above, an SCSI connector is shown. In an IDE/EIDE HDD, there would be a connector similar, but with a different amount of connector pins and settings.

PLATTERS (both sides of each platter are used for storage of data.)

SPINDLE (located in the center of all the platters, and is used to spin the platters.)

ACTUATOR (a mechanical device for moving or controlling the actuator arm.)

ACTUATOR AXIS (sits in the center of the actuator enabling it to move smoothly.)

ACTUATOR ARM (a mechanical arm enabling the HDD read/write heads to extend over & in-between the platters for reading and writing to the HDD.)

SLIDER & HEAD (located at the end of the actuator arm and is the mechanism used to read and write to the platters. A spindle motor spins the spindle - not shown above.)

INTERNAL RIBBON CABLE (attaches heads to the logic board of the HDD.) TRACKS & SECTORS - The diagram above is basic so that you can understand the divisions easier.  Hard disk drive platters are divided up into individual areas consisting of TRACKS & SECTORS.  Look at the diagram above to understand the difference between a track and sector.  You see that a TRACK is one complete ring around the platter, and that a SECTOR is just one part of a track.  You can also see that there are many sectors inside of one track.   Each track in the diagram above has 16 sectors.  (In actuality, there are thousands of tracks on each platter, and they are nowhere near as wide as in the diagram.)  CLUSTERS - Additionally, a CLUSTER is a group of sectors.  Files are stored in clusters. This means that a single file can be stored in many sectors, because the file might be too large to fit in just one sector.  When an HDD becomes fragmented, a single file can become scattered all over the platters.  When the request for the file is sent, the HDD will start thrashing all over the platters trying to get all the parts of the file if the HDD is badly defragmented. CYLINDERS - Understanding CYLINDERS is a bit harder. Imagine that there are 6 platters just like the one above in the diagram.  Each platter is slid onto the SPINDLE so that they are all evenly stacked on top of each other with some space in-between each platter.    Now imagine that each platter is identical and has one green ring on it (a track) just like in the diagram above.  When the platters are stacked, this means that each green ring on each platter is located directly under or above each other.  Imagine drawing an imaginary line from each section, around each track (the inner and outer circle of the track) on one platter, and connecting it to the same green track on the next platter underneath it.  Then do the same to each of the other platters until all of the green tracks are connected together.   If it were possible to take a can with the lid and bottom cut off, and somehow slip it through the platters to fit only in the space where the green tracks are, you would be inside of the CYLINDER.  It is called a cylinder because of the imaginary cylindrical shape that it forms. HARD DRIVE TYPES IDE - Integrated Drive Electronics - put most of the electronics on the drive itself, therefore it controls itself. EIDE - Enhanced Integrated Drive Electronics - improved on the limitations of the IDE drive and allows up to 4 drives on one controller, including non hard disk drives such as CD-ROM drives. SCSI DRIVES - (Small Computer System Interface drives)  Also pronounced as scuzzy drives, they allow the addition of up to 7 devices, scanners or printers in one line, as long as they use the SCSI interface.  They are much faster than IDE/ATA drives, but are also more expensive.  These drives are connected in a row to each other in a daisy-chain fashion. Each SCSI device on the bus  requires a unique SCSI number  from 1-7, with the computer's SCSI number being 0.  Included in SCSI Drives are the following types (also see DATA INTERFACE CONNECTOR above for information on connector types): SCSI 1 SCSI 2 SCSI 3 EXTERNAL HARD DRIVES - External hard drives are connected to the computer outside of the case via a connector interface on the back of the computer.  An example is the QUICK DRIVE which connects to the parallel port connector, and  is a way to add extra hard drives for storage, but does not run as fast as an internal hard drive.  Other QUICK DRIVES connect via the USB or PC CARD  such as those used on laptops.  A newer type of external hard drive by Western Digital are called Fire Wire External Hard Drives .  The IEEE FIREWIRE peripheral interface (also known as 1394 and iLINK) has 30 times more bandwidth than USB, making it the perfect technology for high-speed devices like the latest hard drives, Digital Video (DV) camcorders, CD-RW drives, printers, and scanners.  MEASUREMENT OF HARD DRIVE CAPACITIES Modern Hard Drives capacities are measured in megabytes and gigabytes.  Although computer technology has climbed to capacities as large as terabytes, it is currently not available in the market for the everyday user.  One important note to keep in mind is that  most hard drive manufacturers list hard drives of gigabyte and megabyte capacities by using the 1000 multiplier rather than the true multiplier of 1024 in deciding the capacity of the HDD.  For instance, let's say you go to the store and buy a hard drive that is listed as 8 GB (gigabyte).  After you install it and access the property sheet for your computer and hard drive in Windows, you notice that you are missing some storage space on the hard drive.  Instead of it showing  the HDD as having 8 GB of space, it shows  7. something gigabytes.  In reality , you are not missing any space on the HDD, and there is nothing wrong with it.  The problem, as previously stated, is the incorrect way that manufacturers compute/list the capacity. A quick refresher on bits and bytes: 8 bits = 1 byte 1024 bytes =  1 kilobyte (KB) 1024 kilobytes  =  1 megabyte (MB) 1024 megabytes  =  1 gigabyte  (GB) 1024 gigabytes = 1 terabyte (TB) Using the chart above, change the multiplier of 1024 to 1000, and you will understand how the HDD manufacturers are incorrectly stating the size of the HDD.  Master Boot Record (MBR) When you turn on your PC, the processor has to begin processing. However, your system memory is empty, and the processor doesn't have anything to execute, or really even know where it is. To ensure that the PC can always boot regardless of which BIOS is in the machine, chip makers and BIOS manufacturers arrange so that the processor, once turned on, always starts executing at the same place, FFFF0h. This is discussed in much more detail here. In a similar manner, every hard disk must have a consistent "starting point" where key information is stored about the disk, such as how many partitions it has, what sort of partitions they are, etc. There also needs to be somewhere that the BIOS can load the initial boot program that starts the process of loading the operating system. The place where this information is stored is called the master boot record (MBR). It is also sometimes called the master boot sector or even just the boot sector.