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In many ways, 
our memories make us who we are,

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helping us remember our past,

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learn and retain skills,

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and plan for the future.

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And for the computers that often act
as extensions of ourselves,

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memory plays much the same role,

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whether it's a two-hour movie,

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a two-word text file,

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or the instructions for opening either,

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everything in a computer's memory
takes the form of basic units called bits,

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or binary digits.

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Each of these is stored in a memory cell

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that can switch between two states
for two possible values,

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0 and 1.

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Files and programs consist of millions
of these bits,

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all processed in 
the central processing unit,

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or CPU,

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that acts as the computer's brain.

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And as the number of bits needing
to be processed grows exponentially,

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computer designers face 
a constant struggle

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between size, cost, and speed.

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Like us, computers have short-term memory
for immediate tasks,

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and long-term memory 
for more permanent storage.

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When you run a program,

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your operating system allocates area
within the short-term memory

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for performing those instructions.

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For example, when you press a key
in a word processor,

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the CPU will access one of these locations
to retrieve bits of data.

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It could also modify them,
or create new ones.

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The time this takes is known 
as the memory's latency.

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And because program instructions must be
processed quickly and continuously,

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all locations within the short-term memory
can be accessed in any order,

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hence the name random access memory.

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The most common type of RAM 
is dynamic RAM, or DRAM.

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There, each memory cell consists
of a tiny transistor and a capacitor

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that store electrical charges,

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a 0 when there's no charge,
or a 1 when charged.

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Such memory is called dynamic

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because it only holds charges briefly
before they leak away,

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requiring periodic recharging
to retain data.

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But even its low latency 
of 100 nanoseconds

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is too long for modern CPUs,

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so there's also a small, 
high-speed internal memory cache

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made from static RAM.

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That's usually made up 
of six interlocked transistors

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which don't need refreshing.

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SRAM is the fastest memory 
in a computer system,

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but also the most expensive,

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and takes up three times 
more space than DRAM.

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But RAM and cache can only hold data
as long as they're powered.

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For data to remain
once the device is turned off,

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it must be transferred 
into a long-term storage device,

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which comes in three major types.

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In magnetic storage, 
which is the cheapest,

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data is stored as a magnetic pattern on
a spinning disc coated with magnetic film.

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But because the disc must rotate 
to where the data is located

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in order to be read,

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the latency for such drives is 100,000 
times slower than that of DRAM.

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On the other hand, optical-based storage
like DVD and Blu-ray

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also uses spinning discs,

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but with a reflective coating.

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Bits are encoded as light and dark spots
using a dye that can be read by a laser.

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While optical storage media are cheap
and removable,

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they have even slower latencies 
than magnetic storage

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and lower capacity as well.

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Finally, the newest and fastest types of
long-term storage are solid-state drives,

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like flash sticks.

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These have no moving parts,

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instead using floating gate transistors

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that store bits by trapping 
or removing electrical charges

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within their specially designed 
internal structures.

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So how reliable 
are these billions of bits?

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We tend to think of computer memory
as stable and permanent,

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but it actually degrades fairly quickly.

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The heat generated from a device
and its environment

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will eventually demagnetize hard drives,

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degrade the dye in optical media,

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and cause charge leakage 
in floating gates.

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Solid-state drives 
also have an additional weakness.

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Repeatedly writing to floating gate 
transistors corrodes them,

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eventually rendering them useless.

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With data on most current storage media

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having less than 
a ten-year life expectancy,

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scientists are working to exploit
the physical properties of materials

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down to the quantum level

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in the hopes of making 
memory devices faster,

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smaller,

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and more durable.

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For now, immortality remains out of reach,
for humans and computers alike.