BASICS OF BASICS - BIT
 KIHON NO KIHON  - ビット

Everything in the computer is built
on top of microscopic on/off
switches, they can either be ON or
OFF, 0 or 1. It has TRILOIONS of
them.

So, the minimum amount of
information you can store, 0 or 1,
we all that: a bit.

We call a group of 8 bits: a byte.
1024 bytes are a kilobyte,
1024 kilobytes are a megabyte,
1024 megabytes are a gigabyte,
1024 gigabytes are a terabyte,
1024 terabytes are a petabyte,
....


Your computer has maybe 16 gigabytes
of memory, which is 17179869184
bytes or 137438953472 bits of memory.

It might seem like a lot, but think
about a picture you take with your
phone, it is usually 4032x3020
pixels, a pixel is a dot, if you
zoom in a lot you will be able to
see all the dots. This dot can have
16 million colors, combination of
red green and blue, 1 byte for red 1
byte green 1 byte blue. So this
picture alone in its raw format can
occupy 4032*3020*3 or 36529920 bytes
or around 35 megabytes. Of course we
use different compression methods to
extract patterns of the pixels and
store them with less bytes, and with
compression those pictures are
around 3 megabytes.
            

Its kind of strange to think about
it like that, but probably the best
way to learn it is to make a
computer yourself, check out Ben
Eater's 8 bit computer on youtube.
    
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BASICS OF BASICS - MEMORY
 KIHON NO KIHON  - メモリ

Imaigne your computer's memory is
like a page with squares each square
can contain a value between 0 and
255.

  | computer memory      |
  |......................| 0  - 21
  |......................| 22 - 43
  |......................| 44 - 65
  |......................| 65 - 87
  |......................| 88 -109
  '----------------------'


You can go to each specific square
by knowing its position, starting
from top left 0, 1, 2, 3 etc

This position is called 'address'.
For example, putting 65 on address
55 would look like this:

  | computer memory      |
  |......................| 0  - 21
  |......................| 22 - 43
  |..........65..........| 44 - 65
  |......................| 65 - 87
  |......................| 88 -109
  '----------------------'

One thing to note, is that the
program itself is also in memory.


  | computer memory      |
  |......................| 0  - 21
  |......................| 22 - 43
  |..........65..........| 44 - 65
  |......................| 65 - 87
  |PPPPPPPPPPPP..........| 88 -109
  '----------------------'

There is no difference between code
and data on the modern processors.

Imagine the processor, when you
power on the computer, it will fetch
the memory at address 88 (on our toy
coputer), and start executing the
instructions, which can be things
like 'add', 'multiply', 'compare'
Each instruction has a number as the
processor only knows numbers
e.g. ADD=5, MULTIPLY=6, COMPARE=7.

This is oversimplified model of
how computers work. but it is good
enough to give you intuition,
about how functions and variables
work.

This memory is called RAM, or RANDOM
ACCESS MEMORY, which means it is
easy to go to specific address.

This memory is wiped out when your
computer is powered off. In contrast
with the persistent storage, called
Hard Disk, or just Disk, where you
can save things and find them later
after turning the computer on. The
files you store your program in, are
stored on the disk. When you start
your program, the first thing it
will happen is it will load the file
from disk to memory, and start
running the instructions from memory.

The disk is much slower than RAM,
it takes 100 nanoseconds to read
from RAM, and 150,000 nanoseconds to
read from modern hard disk.

The term disk comes from the fact
that years ago the hard disk was
actually a disk, and a sensitive
magnetic needle was moving to read
and write the data. This is no
longer the case, but the name disk
remained.

Many computer things are named after
things from the past, and make no
sense.  When you 'hangup' the phone,
it used to literally mean to put the
phone on a hook on the wall, not
pressing the hangup button, so dont
be too scared of those names, they
are just names.