Inside a Hard Drive
Intro
Break paragraph 1 into 2 parts before ... A hard disk drive provides
I hope the intro will be broken NON-VOLATILE...
up. Few students will take the
time to read that much text in an End after paragraph 2 ... reads and writes data.
intro. They’ll just start clicking if
the blocks of text are too large. Possibly replace the last 2 paragraphs with:
Discover some of the factors that impact a hard drive’s performance
The extra info can be moved to and how to keep it running at top speed.
the relevant sections.
Anatomy (open view of drive contents)
The platters, which are coated with a thin, magnetically-sensitive
Ideally, this would be great if the coating where the data is stored, sit of top of the DC spindle motor
open drive section could appear which draws power from the computer’s power supply to keep the
in 2 parts to make it more platters spinning at a precise, constant speed of thousands of
interactive. The spindle and revolutions per minute (rpm) from the moment the computer is turned
platters first, then the actuators, on until the power goes off.
arms and r/w heads.
The actuators move the arms from the center to the outer edge of each
platter at amazing speeds (as fast a 50 times a second!) allowing the
read/write heads to reach every possible bit of data. The read/write
heads don't touch the platter when it is spinning but float on a very thin
cushion of air.
(optional)
A typical hard drive has 2 or more platters. Large-capacity drives
have more platters, and record data on both the tops and bottoms of
the platters.
(closed view of hard drive)
The hard drive case should always remain sealed shut. If as much as a
speck of dust makes it way into the hard drive case, it can cause a
scratch, which will destroy data and possibly cause a hard drive
“crash” where the drive not longer functions.
Writing (binary code writing on drive)
Everything the computer stores is written in a binary code of 0’s and
1’s. (bits) The read/write heads record each bit of information with
lightning speed as the platter rotates underneath. All of the available
space on one ring around the disk is filled at a time.
(tracks and sectors)
Before any information can be recorded on the hard drive, it must be
formatted. Formatting marks the disk into tracks (rings) and sectors
(wedges) as shown. This gives the computer a system to determine the
location of each bit of data.
(optional)
Modern hard drives divide the outer tracks, where there is more room,
into a greater number of sectors than the smaller, inner tracks.
Reading 1- (initial display) When information stored on the hard drive has
been requested, the controller sends a signal to the drive. The
I’d really like it if the color of drive looks up the location of the starting track and sector,
the data chunk coming off the moves the arm to the appropriate track and waits for the sector
drive matched the color bar at to pass under the read/write head.
the bottom of the screen display 2- (after the first chunk of data has been delivered) As each block
showing its arrival. (both red) of data is located, the hard drive sends it along the bus lines to
the computer and seeks the next block of data.
3- (after the second chunk) Each block of information contains a
marking at the end to tell whether to continue on to anther
sector or it is the last piece of data in the file
4- (after the third chunk) Even after all of the data has been
delivered, the drive continues to spin, awaiting the next
request.
Fragmentation Initially, when a drive is empty, data is recorded onto it in contiguous
blocks as each new file is saved on the disk. The number of sectors
required depends on the size of the file being stored.
[Optionally: Obviously it takes more storage space to store a long
song than a short one!]
(continue until the songs have been saved - pause display here with a
continue or next button)
But, as old files are deleted, the free space becomes scattered across
the disk.
(delete one file, pause again)
As more files are deleted, and new files are written to the disk, the
pieces become more and more disjoint. The disk becomes fragmented.
Fragmentation means that pieces of each file are spread out all over
the disk.
(continue to the end where display says “eventually the disk becomes
severely fragmented)
Defrag When a drive becomes severely fragmented it slows the computer
down because it takes more time to search for and locate all of a file’s
parts.
Running a disk defragmentation program takes all of the separated
pieces and puts them back together making the computer run much
more efficiently because it increases the speed to access and retrieve
information
Rotational delay It only takes a few milliseconds from the time a computer requests a
file and the first bit of information is ready to be delivered. The correct
platter must be selected and the arm must be moved to the right track
and sector. This is called the access time.
The tiny delay experienced after the read/write head is positioned over
the correct track, while the head waits for the right sector to pass
underneath, is called rotational latency. The faster the drive spins, the
less rotational latency there is.
(under short delay)
The access time for a piece of data that is located in the next sector to
pass under the read/write head is much less than the access time for
data that is on a different track and sector.
(under long delays)
Even though these delays are measured in milliseconds, they add up
and cause a noticeable delay in the time it takes for programs to start
running or files to open.
References:
http://www4.tomshardware.com/storage/19970728/
http://www.hardwarecentral.com/hardwarecentral/tutorials/41/6/
http://www.webopedia.com
http://www.webopedia.com/Hardware/Data_Storage/Disk_Drives/Hard_Disk_Drives/
http://www.howstuffworks.com