0:00:07.248,0:00:10.821 Imagine an airplane flying[br]one millimeter above the ground 0:00:10.821,0:00:14.029 and circling the Earth[br]once every 25 seconds 0:00:14.029,0:00:17.335 while counting every blade of grass. 0:00:17.335,0:00:20.551 Shrink all that down so that it fits[br]in the palm of your hand, 0:00:20.551,0:00:24.305 and you'd have something equivalent[br]to a modern hard drive, 0:00:24.305,0:00:28.455 an object that can likely hold[br]more information than your local library. 0:00:28.455,0:00:32.906 So how does it store so much information[br]in such a small space? 0:00:32.906,0:00:37.122 At the heart of every hard drive[br]is a stack of high-speed spinning discs 0:00:37.122,0:00:40.525 with a recording head [br]flying over each surface. 0:00:40.525,0:00:46.278 Each disc is coated with a film[br]of microscopic magnetised metal grains, 0:00:46.278,0:00:49.591 and your data doesn't live there[br]in a form you can recognize. 0:00:49.591,0:00:52.768 Instead, it is recorded [br]as a magnetic pattern 0:00:52.768,0:00:55.819 formed by groups of those tiny grains. 0:00:55.819,0:00:58.169 In each group, also known as a bit, 0:00:58.169,0:01:01.121 all of the grains have [br]their magnetization's aligned 0:01:01.121,0:01:03.596 in one of two possible states, 0:01:03.596,0:01:06.805 which correspond to zeroes and ones. 0:01:06.805,0:01:08.668 Data is written onto the disc 0:01:08.668,0:01:12.577 by converting strings of bits [br]into electrical current 0:01:12.577,0:01:14.994 fed through an electromagnet. 0:01:14.994,0:01:18.613 This magnet generates a field[br]strong enough to change the direction 0:01:18.613,0:01:21.145 of the metal grain's magnetization. 0:01:21.145,0:01:24.102 Once this information is written [br]onto the disc, 0:01:24.102,0:01:28.843 the drive uses a magnetic reader[br]to turn it back into a useful form, 0:01:28.843,0:01:33.468 much like a phonograph needle[br]translates a record's grooves into music. 0:01:33.468,0:01:37.634 But how can you get so much information[br]out of just zeroes and ones? 0:01:37.634,0:01:40.300 Well, by putting lots of them together. 0:01:40.300,0:01:45.246 For example, a letter is represented[br]in one byte, or eight bits, 0:01:45.246,0:01:47.879 and your average photo [br]takes up several megabytes, 0:01:47.879,0:01:50.865 each of which is 8 million bits. 0:01:50.865,0:01:54.779 Because each bit must be written onto[br]a physical area of the disc, 0:01:54.779,0:01:58.833 we're always seeking to increase[br]the disc's areal density, 0:01:58.833,0:02:03.572 or how many bits can be squeezed[br]into one square inch. 0:02:03.572,0:02:08.907 The areal density of a modern hard drive[br]is about 600 gigabits per square inch, 0:02:08.907,0:02:15.524 300 million times greater than that[br]of IBM's first hard drive from 1957. 0:02:15.524,0:02:17.929 This amazing advance in storage capacity 0:02:17.929,0:02:20.732 wasn't just a matter [br]of making everything smaller, 0:02:20.732,0:02:22.914 but involved multiple innovations. 0:02:22.914,0:02:26.153 A technique called the thin film[br]lithography process 0:02:26.153,0:02:29.847 allowed engineers [br]to shrink the reader and writer. 0:02:29.847,0:02:32.767 And despite its size, [br]the reader became more sensitive 0:02:32.767,0:02:39.090 by taking advantage of new discoveries in[br]magnetic and quantum properties of matter. 0:02:39.090,0:02:43.384 Bits could also be packed closer together[br]thanks to mathematical algorithms 0:02:43.384,0:02:46.600 that filter out noise[br]from magnetic interference, 0:02:46.600,0:02:51.474 and find the most likely bit sequences[br]from each chunk of read-back signal. 0:02:51.474,0:02:54.465 And thermal expansion control of the head, 0:02:54.465,0:02:57.548 enabled by placing a heater [br]under the magnetic writer, 0:02:57.548,0:03:02.675 allowed it to fly less than[br]five nanometers above the disc's surface, 0:03:02.675,0:03:06.661 about the width of two strands of DNA. 0:03:06.661,0:03:08.417 For the past several decades, 0:03:08.417,0:03:12.564 the exponential growth in computer[br]storage capacity and processing power 0:03:12.564,0:03:15.816 has followed a pattern [br]known as Moore's Law, 0:03:15.816,0:03:23.099 which, in 1975, predicted that information[br]density would double every two years. 0:03:23.099,0:03:25.993 But at around 100 gigabits [br]per square inch, 0:03:25.993,0:03:30.185 shrinking the magnetic grains further[br]or cramming them closer together 0:03:30.185,0:03:34.361 posed a new risk[br]called the superparamagnetic effect. 0:03:34.361,0:03:37.545 When a magnetic grain volume is too small, 0:03:37.545,0:03:41.476 its magnetization is easily disturbed[br]by heat energy 0:03:41.476,0:03:44.429 and can cause bits [br]to switch unintentionally, 0:03:44.429,0:03:46.714 leading to data loss. 0:03:46.714,0:03:50.819 Scientists resolved this limitation[br]in a remarkably simple way: 0:03:50.819,0:03:55.899 by changing the direction of recording[br]from longitudinal to perpendicular, 0:03:55.899,0:04:01.225 allowing areal density to approach[br]one terabit per square inch. 0:04:01.225,0:04:04.858 Recently, the potential limit has been[br]increased yet again 0:04:04.858,0:04:07.682 through heat assisted magnetic recording. 0:04:07.682,0:04:11.451 This uses an even more thermally[br]stable recording medium, 0:04:11.451,0:04:14.889 whose magnetic resistance [br]is momentarily reduced 0:04:14.889,0:04:18.517 by heating up a particular spot [br]with a laser 0:04:18.517,0:04:20.535 and allowing data to be written. 0:04:20.535,0:04:23.557 And while those drives are currently[br]in the prototype stage, 0:04:23.557,0:04:28.295 scientists already have the next potential[br]trick up their sleeves: 0:04:28.295,0:04:30.291 bit-patterned media, 0:04:30.291,0:04:35.267 where bit locations are arranged [br]in separate, nano-sized structures, 0:04:35.267,0:04:40.303 potentially allowing for areal densities[br]of twenty terabits per square inch 0:04:40.303,0:04:41.780 or more. 0:04:41.780,0:04:46.247 So it's thanks to the combined efforts[br]of generations of engineers, 0:04:46.247,0:04:48.014 material scientists, 0:04:48.014,0:04:49.976 and quantum physicists 0:04:49.976,0:04:53.019 that this tool of incredible power[br]and precision 0:04:53.019,0:04:55.814 can spin in the palm of your hand.