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A desk and a filing cabinet

Where Does a Computer Keep Things?

A computer has two quite different places to put things, and the difference is what happens when the power goes off.

Working memory Fast, small, emptieswhen offStorage Slower, huge, keepseverything
A desk you clear each night, and a cabinet you do not.

  1. Step 1 of 5

    Working memory is the desk.

    1 A file isopened fromstorage2 It is copiedonto the fastdesk3 Power off — thedesk is wiped

    Whatever a computer is doing right now sits in fast memory. It is small and expensive, and it forgets everything the instant the power stops — which is why unsaved work vanishes.

  2. Step 2 of 5

    Storage is the filing cabinet.

    Working memorysmall, andextremely fastStoragehundreds oftimes bigger,much slower

    Storage holds far more and keeps it without power, but reaching it is much slower. So the computer copies what it needs onto the desk, works there, and files it back.

  3. Step 3 of 5

    Everything is stored as on or off.

    A photo on screen A long row of on-or-offswitches

    Every photo, song and message is a very long row of switches, each on or off. What makes one a picture and another a song is only which program reads it and how.

  4. Step 4 of 5

    Guessing what you need next.

    Fetched from storage once Kept close byafterwards The second open is instant Old items aredropped tomake room

    Computers fetch things before you ask, keeping recent items close by. When an app opens instantly the second time, it is because it was never really put away.

  5. Step 5 of 5

    The cloud is a filing cabinet elsewhere.

    On your machine Yours, and workswithout internetIn the cloud Elsewhere, and needs aconnection

    Files in the cloud are on someone else's storage in a building somewhere, reached over the internet. The convenience is real; so is the fact that it is not your cabinet.

    This is why turning it off and on again works so often. It empties the desk completely and starts clean.

The short version

A computer works in fast memory that empties at power-off and files things in slower storage that does not.

Try it yourself

Open a big app twice in a row. The second time is much quicker — it was still on the desk.

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