[Script Info]
Title: 
[Events]
Format: Layer, Start, End, Style, Name, MarginL, MarginR, MarginV, Effect, Text
Dialogue: 0,0:00:06.88,0:00:10.03,Default,,0000,0000,0000,,In many ways, \Nour memories make us who we are,
Dialogue: 0,0:00:10.03,0:00:12.06,Default,,0000,0000,0000,,helping us remember our past,
Dialogue: 0,0:00:12.06,0:00:13.99,Default,,0000,0000,0000,,learn and retain skills,
Dialogue: 0,0:00:13.99,0:00:16.27,Default,,0000,0000,0000,,and plan for the future.
Dialogue: 0,0:00:16.27,0:00:19.92,Default,,0000,0000,0000,,And for the computers that often act\Nas extensions of ourselves,
Dialogue: 0,0:00:19.92,0:00:22.13,Default,,0000,0000,0000,,memory plays much the same role,
Dialogue: 0,0:00:22.13,0:00:23.71,Default,,0000,0000,0000,,whether it's a two-hour movie,
Dialogue: 0,0:00:23.71,0:00:25.28,Default,,0000,0000,0000,,a two-word text file,
Dialogue: 0,0:00:25.28,0:00:27.83,Default,,0000,0000,0000,,or the instructions for opening either,
Dialogue: 0,0:00:27.83,0:00:33.37,Default,,0000,0000,0000,,everything in a computer's memory\Ntakes the form of basic units called bits,
Dialogue: 0,0:00:33.37,0:00:35.85,Default,,0000,0000,0000,,or binary digits.
Dialogue: 0,0:00:35.85,0:00:38.39,Default,,0000,0000,0000,,Each of these is stored in a memory cell
Dialogue: 0,0:00:38.39,0:00:42.18,Default,,0000,0000,0000,,that can switch between two states\Nfor two possible values,
Dialogue: 0,0:00:42.18,0:00:44.06,Default,,0000,0000,0000,,0 and 1.
Dialogue: 0,0:00:44.06,0:00:47.18,Default,,0000,0000,0000,,Files and programs consist of millions\Nof these bits,
Dialogue: 0,0:00:47.18,0:00:50.43,Default,,0000,0000,0000,,all processed in \Nthe central processing unit,
Dialogue: 0,0:00:50.43,0:00:51.75,Default,,0000,0000,0000,,or CPU,
Dialogue: 0,0:00:51.75,0:00:54.10,Default,,0000,0000,0000,,that acts as the computer's brain.
Dialogue: 0,0:00:54.10,0:00:58.67,Default,,0000,0000,0000,,And as the number of bits needing\Nto be processed grows exponentially,
Dialogue: 0,0:00:58.67,0:01:01.53,Default,,0000,0000,0000,,computer designers face \Na constant struggle
Dialogue: 0,0:01:01.53,0:01:05.30,Default,,0000,0000,0000,,between size, cost, and speed.
Dialogue: 0,0:01:05.30,0:01:10.13,Default,,0000,0000,0000,,Like us, computers have short-term memory\Nfor immediate tasks,
Dialogue: 0,0:01:10.13,0:01:13.41,Default,,0000,0000,0000,,and long-term memory \Nfor more permanent storage.
Dialogue: 0,0:01:13.41,0:01:15.28,Default,,0000,0000,0000,,When you run a program,
Dialogue: 0,0:01:15.28,0:01:18.95,Default,,0000,0000,0000,,your operating system allocates area\Nwithin the short-term memory
Dialogue: 0,0:01:18.95,0:01:20.84,Default,,0000,0000,0000,,for performing those instructions.
Dialogue: 0,0:01:20.84,0:01:24.39,Default,,0000,0000,0000,,For example, when you press a key\Nin a word processor,
Dialogue: 0,0:01:24.39,0:01:29.54,Default,,0000,0000,0000,,the CPU will access one of these locations\Nto retrieve bits of data.
Dialogue: 0,0:01:29.54,0:01:33.86,Default,,0000,0000,0000,,It could also modify them,\Nor create new ones.
Dialogue: 0,0:01:33.86,0:01:38.26,Default,,0000,0000,0000,,The time this takes is known \Nas the memory's latency.
Dialogue: 0,0:01:38.26,0:01:43.80,Default,,0000,0000,0000,,And because program instructions must be\Nprocessed quickly and continuously,
Dialogue: 0,0:01:43.80,0:01:48.56,Default,,0000,0000,0000,,all locations within the short-term memory\Ncan be accessed in any order,
Dialogue: 0,0:01:48.56,0:01:51.71,Default,,0000,0000,0000,,hence the name random access memory.
Dialogue: 0,0:01:51.71,0:01:55.90,Default,,0000,0000,0000,,The most common type of RAM \Nis dynamic RAM, or DRAM.
Dialogue: 0,0:01:55.90,0:02:00.99,Default,,0000,0000,0000,,There, each memory cell consists\Nof a tiny transistor and a capacitor
Dialogue: 0,0:02:00.99,0:02:02.99,Default,,0000,0000,0000,,that store electrical charges,
Dialogue: 0,0:02:02.99,0:02:07.56,Default,,0000,0000,0000,,a 0 when there's no charge,\Nor a 1 when charged.
Dialogue: 0,0:02:07.56,0:02:09.17,Default,,0000,0000,0000,,Such memory is called dynamic
Dialogue: 0,0:02:09.17,0:02:13.38,Default,,0000,0000,0000,,because it only holds charges briefly\Nbefore they leak away,
Dialogue: 0,0:02:13.38,0:02:16.76,Default,,0000,0000,0000,,requiring periodic recharging\Nto retain data.
Dialogue: 0,0:02:16.76,0:02:20.01,Default,,0000,0000,0000,,But even its low latency \Nof 100 nanoseconds
Dialogue: 0,0:02:20.01,0:02:22.65,Default,,0000,0000,0000,,is too long for modern CPUs,
Dialogue: 0,0:02:22.65,0:02:26.56,Default,,0000,0000,0000,,so there's also a small, \Nhigh-speed internal memory cache
Dialogue: 0,0:02:26.56,0:02:28.51,Default,,0000,0000,0000,,made from static RAM.
Dialogue: 0,0:02:28.51,0:02:31.72,Default,,0000,0000,0000,,That's usually made up \Nof six interlocked transistors
Dialogue: 0,0:02:31.72,0:02:33.62,Default,,0000,0000,0000,,which don't need refreshing.
Dialogue: 0,0:02:33.62,0:02:36.78,Default,,0000,0000,0000,,SRAM is the fastest memory \Nin a computer system,
Dialogue: 0,0:02:36.78,0:02:38.68,Default,,0000,0000,0000,,but also the most expensive,
Dialogue: 0,0:02:38.68,0:02:42.41,Default,,0000,0000,0000,,and takes up three times \Nmore space than DRAM.
Dialogue: 0,0:02:42.41,0:02:46.60,Default,,0000,0000,0000,,But RAM and cache can only hold data\Nas long as they're powered.
Dialogue: 0,0:02:46.60,0:02:49.62,Default,,0000,0000,0000,,For data to remain\Nonce the device is turned off,
Dialogue: 0,0:02:49.62,0:02:53.00,Default,,0000,0000,0000,,it must be transferred \Ninto a long-term storage device,
Dialogue: 0,0:02:53.00,0:02:55.29,Default,,0000,0000,0000,,which comes in three major types.
Dialogue: 0,0:02:55.29,0:02:57.74,Default,,0000,0000,0000,,In magnetic storage, \Nwhich is the cheapest,
Dialogue: 0,0:02:57.74,0:03:03.56,Default,,0000,0000,0000,,data is stored as a magnetic pattern on\Na spinning disc coded with magnetic film.
Dialogue: 0,0:03:03.56,0:03:07.20,Default,,0000,0000,0000,,But because the disc must rotate \Nto where the data is located
Dialogue: 0,0:03:07.20,0:03:08.62,Default,,0000,0000,0000,,in order to be read,
Dialogue: 0,0:03:08.62,0:03:14.51,Default,,0000,0000,0000,,the latency for such drives is 100,000 \Ntimes slower than that of DRAM.
Dialogue: 0,0:03:14.51,0:03:18.63,Default,,0000,0000,0000,,On the other hand, optical-based storage\Nlike DVD and Blu-ray
Dialogue: 0,0:03:18.63,0:03:20.62,Default,,0000,0000,0000,,also uses spinning discs,
Dialogue: 0,0:03:20.62,0:03:22.81,Default,,0000,0000,0000,,but with a reflective coating.
Dialogue: 0,0:03:22.81,0:03:28.03,Default,,0000,0000,0000,,Bits are encoded as light and dark spots\Nusing a dye that can be read by a laser.
Dialogue: 0,0:03:28.03,0:03:31.15,Default,,0000,0000,0000,,While optical storage media are cheap\Nand removable,
Dialogue: 0,0:03:31.15,0:03:34.88,Default,,0000,0000,0000,,they have even slower latencies \Nthan magnetic storage
Dialogue: 0,0:03:34.88,0:03:37.24,Default,,0000,0000,0000,,and lower capacity as well.
Dialogue: 0,0:03:37.24,0:03:42.87,Default,,0000,0000,0000,,Finally, the newest and fastest types of\Nlong-term storage are solid-state drives,
Dialogue: 0,0:03:42.87,0:03:44.02,Default,,0000,0000,0000,,like flash sticks.
Dialogue: 0,0:03:44.02,0:03:45.96,Default,,0000,0000,0000,,These have no moving parts,
Dialogue: 0,0:03:45.96,0:03:48.63,Default,,0000,0000,0000,,instead using floating gate transistors
Dialogue: 0,0:03:48.63,0:03:53.13,Default,,0000,0000,0000,,that store bits by trapping \Nor removing electrical charges
Dialogue: 0,0:03:53.13,0:03:56.45,Default,,0000,0000,0000,,within their specially designed \Ninternal structures.
Dialogue: 0,0:03:56.45,0:03:59.74,Default,,0000,0000,0000,,So how reliable \Nare these billions of bits?
Dialogue: 0,0:03:59.74,0:04:03.46,Default,,0000,0000,0000,,We tend to think of computer memory\Nas stable and permanent,
Dialogue: 0,0:04:03.46,0:04:06.36,Default,,0000,0000,0000,,but it actually degrades fairly quickly.
Dialogue: 0,0:04:06.36,0:04:09.00,Default,,0000,0000,0000,,The heat generated from a device\Nand its environment
Dialogue: 0,0:04:09.00,0:04:11.74,Default,,0000,0000,0000,,will eventually demagnetize hard drives,
Dialogue: 0,0:04:11.74,0:04:13.99,Default,,0000,0000,0000,,degrade the dye in optical media,
Dialogue: 0,0:04:13.99,0:04:17.12,Default,,0000,0000,0000,,and cause charge leakage \Nin floating gates.
Dialogue: 0,0:04:17.12,0:04:20.08,Default,,0000,0000,0000,,Solid-state drives \Nalso have an additional weakness.
Dialogue: 0,0:04:20.08,0:04:24.10,Default,,0000,0000,0000,,Repeatedly writing to floating gate \Ntransistors corrodes them,
Dialogue: 0,0:04:24.10,0:04:26.70,Default,,0000,0000,0000,,eventually rendering them useless.
Dialogue: 0,0:04:26.70,0:04:29.22,Default,,0000,0000,0000,,With data on most current storage media
Dialogue: 0,0:04:29.22,0:04:31.96,Default,,0000,0000,0000,,having less than \Na ten-year life expectancy,
Dialogue: 0,0:04:31.96,0:04:36.33,Default,,0000,0000,0000,,scientists are working to exploit\Nthe physical properties of materials
Dialogue: 0,0:04:36.33,0:04:38.65,Default,,0000,0000,0000,,down to the quantum level
Dialogue: 0,0:04:38.65,0:04:40.100,Default,,0000,0000,0000,,in the hopes of making \Nmemory devices faster,
Dialogue: 0,0:04:40.100,0:04:42.06,Default,,0000,0000,0000,,smaller,
Dialogue: 0,0:04:42.06,0:04:43.61,Default,,0000,0000,0000,,and more durable.
Dialogue: 0,0:04:43.61,0:04:49.04,Default,,0000,0000,0000,,For now, immortality remains out of reach,\Nfor humans and computers alike.