TedTest

From the Ted Talk by Kanawat Senanan: How do hard drives work?

Unscramble the Blue Letters

Imagine an airplane flying one millimeter above the ground and circling the Earth once every 25 seconds while counting every badle of grass. Shrink all that down so that it fits in the palm of your hand, and you'd have something equivalent to a modern hard drive, an object that can likely hold more information than your local library. So how does it store so much information in such a slaml space? At the heart of every hard drive is a stack of high-speed spinning discs with a recording head flniyg over each saucfre. Each disc is coated with a film of microscopic magnetised metal grains, and your data doesn't live there in a form you can recognize. Instead, it is recorded as a magnetic pattern formed by groups of those tiny grains. In each gurop, also known as a bit, all of the grains have their magnetization's aligned in one of two possible seatts, which crsoponred to zeroes and ones. Data is written onto the disc by converting srgtins of bits into ecailetcrl current fed through an electromagnet. This magnet generates a field strong enough to change the direction of the metal grain's magnetization. Once this information is wrtiten onto the disc, the drive uses a magnetic reader to turn it back into a useful form, much like a phonograph needle translates a record's grooves into music. But how can you get so much information out of just zeroes and ones? Well, by putting lots of them together. For example, a letter is represented in one byte, or eight bits, and your average photo tkaes up several megabytes, each of which is 8 million bits. Because each bit must be written onto a physical area of the disc, we're always seeking to increase the disc's areal density, or how many bits can be squeezed into one square inch. The areal density of a mdoern hard drive is about 600 gigabits per square inch, 300 million tmeis greater than that of IBM's first hard dirve from 1957. This amazing advance in storage capacity wasn't just a mttear of making everything smaller, but involved multiple innovations. A technique called the thin film lithography posercs alwoled engineers to shrink the rdeaer and writer. And despite its size, the reader became more sensitive by taking advantage of new discoveries in magnetic and quantum properties of matter. Bits could also be packed closer together thanks to mathematical algorithms that fliter out noise from magnetic interference, and find the most likely bit seeuenqcs from each chunk of read-back signal. And thermal expansion control of the head, enabled by placing a heater under the magnetic writer, allowed it to fly less than five nanometers above the disc's surface, about the width of two strands of DNA. For the past several deadecs, the exponential growth in computer storage capacity and processing power has followed a pattern known as Moore's Law, which, in 1975, predicted that information density would double every two years. But at around 100 gigabits per square inch, shrinking the magnetic grains further or cramming them closer together peosd a new risk called the superparamagnetic effect. When a maentgic grain volume is too small, its matzgoiaenitn is easliy disturbed by heat energy and can cause bits to sitwch unintentionally, leading to data loss. sietctsins resolved this limitation in a remarkably simple way: by changing the direction of rdrceoing from longitudinal to perpendicular, allowing areal density to acpoprah one teirabt per square inch. Recently, the potential limit has been iescearnd yet again through heat assisted magnetic recording. This uses an even more tlhearlmy stlabe recording meidum, whose magnetic resistance is momentarily reduced by htaieng up a particular spot with a laser and allowing data to be written. And while those drives are currently in the prototype sagte, scientists already have the next potential trick up their sleeves: bit-patterned media, where bit locations are arranged in separate, nano-sized structures, potentially allowing for aaerl densities of tenwty terabits per square inch or more. So it's thanks to the combined ertffos of generations of engineers, mteiaral scientists, and quantum pissihycts that this tool of ilrincdebe power and precision can spin in the palm of your hand.

Open Cloze

Imagine an airplane flying one millimeter above the ground and circling the Earth once every 25 seconds while counting every _____ of grass. Shrink all that down so that it fits in the palm of your hand, and you'd have something equivalent to a modern hard drive, an object that can likely hold more information than your local library. So how does it store so much information in such a _____ space? At the heart of every hard drive is a stack of high-speed spinning discs with a recording head ______ over each _______. Each disc is coated with a film of microscopic magnetised metal grains, and your data doesn't live there in a form you can recognize. Instead, it is recorded as a magnetic pattern formed by groups of those tiny grains. In each _____, also known as a bit, all of the grains have their magnetization's aligned in one of two possible ______, which __________ to zeroes and ones. Data is written onto the disc by converting _______ of bits into __________ current fed through an electromagnet. This magnet generates a field strong enough to change the direction of the metal grain's magnetization. Once this information is _______ onto the disc, the drive uses a magnetic reader to turn it back into a useful form, much like a phonograph needle translates a record's grooves into music. But how can you get so much information out of just zeroes and ones? Well, by putting lots of them together. For example, a letter is represented in one byte, or eight bits, and your average photo _____ up several megabytes, each of which is 8 million bits. Because each bit must be written onto a physical area of the disc, we're always seeking to increase the disc's areal density, or how many bits can be squeezed into one square inch. The areal density of a ______ hard drive is about 600 gigabits per square inch, 300 million _____ greater than that of IBM's first hard _____ from 1957. This amazing advance in storage capacity wasn't just a ______ of making everything smaller, but involved multiple innovations. A technique called the thin film lithography _______ _______ engineers to shrink the ______ and writer. And despite its size, the reader became more sensitive by taking advantage of new discoveries in magnetic and quantum properties of matter. Bits could also be packed closer together thanks to mathematical algorithms that ______ out noise from magnetic interference, and find the most likely bit _________ from each chunk of read-back signal. And thermal expansion control of the head, enabled by placing a heater under the magnetic writer, allowed it to fly less than five nanometers above the disc's surface, about the width of two strands of DNA. For the past several _______, the exponential growth in computer storage capacity and processing power has followed a pattern known as Moore's Law, which, in 1975, predicted that information density would double every two years. But at around 100 gigabits per square inch, shrinking the magnetic grains further or cramming them closer together _____ a new risk called the superparamagnetic effect. When a ________ grain volume is too small, its _____________ is ______ disturbed by heat energy and can cause bits to ______ unintentionally, leading to data loss. __________ resolved this limitation in a remarkably simple way: by changing the direction of _________ from longitudinal to perpendicular, allowing areal density to ________ one _______ per square inch. Recently, the potential limit has been _________ yet again through heat assisted magnetic recording. This uses an even more _________ ______ recording ______, whose magnetic resistance is momentarily reduced by _______ up a particular spot with a laser and allowing data to be written. And while those drives are currently in the prototype _____, scientists already have the next potential trick up their sleeves: bit-patterned media, where bit locations are arranged in separate, nano-sized structures, potentially allowing for _____ densities of ______ terabits per square inch or more. So it's thanks to the combined _______ of generations of engineers, ________ scientists, and quantum __________ that this tool of __________ power and precision can spin in the palm of your hand.

Solution

modern
efforts
incredible
stage
flying
decades
physicists
takes
small
group
filter
states
areal
surface
material
scientists
medium
recording
blade
terabit
reader
drive
strings
sequences
correspond
twenty
times
posed
easily
magnetization
written
magnetic
thermally
approach
switch
process
increased
matter
allowed
heating
electrical
stable

Original Text

Imagine an airplane flying one millimeter above the ground and circling the Earth once every 25 seconds while counting every blade of grass. Shrink all that down so that it fits in the palm of your hand, and you'd have something equivalent to a modern hard drive, an object that can likely hold more information than your local library. So how does it store so much information in such a small space? At the heart of every hard drive is a stack of high-speed spinning discs with a recording head flying over each surface. Each disc is coated with a film of microscopic magnetised metal grains, and your data doesn't live there in a form you can recognize. Instead, it is recorded as a magnetic pattern formed by groups of those tiny grains. In each group, also known as a bit, all of the grains have their magnetization's aligned in one of two possible states, which correspond to zeroes and ones. Data is written onto the disc by converting strings of bits into electrical current fed through an electromagnet. This magnet generates a field strong enough to change the direction of the metal grain's magnetization. Once this information is written onto the disc, the drive uses a magnetic reader to turn it back into a useful form, much like a phonograph needle translates a record's grooves into music. But how can you get so much information out of just zeroes and ones? Well, by putting lots of them together. For example, a letter is represented in one byte, or eight bits, and your average photo takes up several megabytes, each of which is 8 million bits. Because each bit must be written onto a physical area of the disc, we're always seeking to increase the disc's areal density, or how many bits can be squeezed into one square inch. The areal density of a modern hard drive is about 600 gigabits per square inch, 300 million times greater than that of IBM's first hard drive from 1957. This amazing advance in storage capacity wasn't just a matter of making everything smaller, but involved multiple innovations. A technique called the thin film lithography process allowed engineers to shrink the reader and writer. And despite its size, the reader became more sensitive by taking advantage of new discoveries in magnetic and quantum properties of matter. Bits could also be packed closer together thanks to mathematical algorithms that filter out noise from magnetic interference, and find the most likely bit sequences from each chunk of read-back signal. And thermal expansion control of the head, enabled by placing a heater under the magnetic writer, allowed it to fly less than five nanometers above the disc's surface, about the width of two strands of DNA. For the past several decades, the exponential growth in computer storage capacity and processing power has followed a pattern known as Moore's Law, which, in 1975, predicted that information density would double every two years. But at around 100 gigabits per square inch, shrinking the magnetic grains further or cramming them closer together posed a new risk called the superparamagnetic effect. When a magnetic grain volume is too small, its magnetization is easily disturbed by heat energy and can cause bits to switch unintentionally, leading to data loss. Scientists resolved this limitation in a remarkably simple way: by changing the direction of recording from longitudinal to perpendicular, allowing areal density to approach one terabit per square inch. Recently, the potential limit has been increased yet again through heat assisted magnetic recording. This uses an even more thermally stable recording medium, whose magnetic resistance is momentarily reduced by heating up a particular spot with a laser and allowing data to be written. And while those drives are currently in the prototype stage, scientists already have the next potential trick up their sleeves: bit-patterned media, where bit locations are arranged in separate, nano-sized structures, potentially allowing for areal densities of twenty terabits per square inch or more. So it's thanks to the combined efforts of generations of engineers, material scientists, and quantum physicists that this tool of incredible power and precision can spin in the palm of your hand.

Frequently Occurring Word Combinations

ngrams of length 2

collocation	frequency
hard drive	3
square inch	3
modern hard	2
areal density	2
storage capacity	2

Important Words

advance
advantage
airplane
algorithms
aligned
allowed
allowing
amazing
approach
area
areal
arranged
assisted
average
bit
bits
blade
byte
called
capacity
change
changing
chunk
circling
closer
coated
combined
computer
control
converting
correspond
counting
cramming
current
data
decades
densities
density
direction
disc
discoveries
discs
disturbed
dna
double
drive
drives
earth
easily
effect
efforts
electrical
electromagnet
enabled
energy
engineers
equivalent
expansion
exponential
fed
field
film
filter
find
fits
fly
flying
form
formed
generates
generations
gigabits
grain
grains
grass
greater
grooves
ground
group
groups
growth
hand
hard
head
heart
heat
heater
heating
hold
imagine
inch
increase
increased
incredible
information
innovations
interference
involved
laser
law
leading
letter
library
limit
limitation
lithography
live
local
locations
longitudinal
loss
lots
magnet
magnetic
magnetised
magnetization
making
material
mathematical
matter
media
medium
megabytes
metal
microscopic
millimeter
million
modern
momentarily
multiple
music
nanometers
needle
noise
object
packed
palm
pattern
perpendicular
phonograph
photo
physical
physicists
placing
posed
potential
potentially
power
precision
predicted
process
processing
properties
prototype
putting
quantum
reader
recognize
recorded
recording
reduced
remarkably
represented
resistance
resolved
risk
scientists
seconds
seeking
sensitive
separate
sequences
shrink
shrinking
signal
simple
size
small
smaller
space
spin
spinning
spot
square
squeezed
stable
stack
stage
states
storage
store
strands
strings
strong
structures
superparamagnetic
surface
switch
takes
technique
terabit
terabits
thermal
thermally
thin
times
tiny
tool
translates
trick
turn
twenty
unintentionally
volume
width
writer
written
years
zeroes