Computers from scratch

~2 mins read

From scratch

numbers

writing

electricity

electron movement = current

the cause of electron movement can be magnetism + moving parts or chemical

no current/current

open/close

0/1

base 2

boolean logic, AND OR NOT IF

mechanical switch

vacuum tube

transistor npn pnp

logic gates

memory cells

bit

byte

Data types

Everything is bytes in memory. We define how should the computer interpret bytes. For example, take the byte 0101001. If looked as text, it’s the letter ‘A’. The computer could interpret it as a color pixel if the same byte were in a movie file, or as part of a song.

int

unsigned int

long

short

double

float

decimal

bool

char

string

unicode

utf8

Computer organization

fetch-decode-execute

CPU = ALU + control unit + memory unit

memory

disk

Instructions

opcode operand

LOAD 0010

ADD 0001 0100

PUSH

POP

JUMP

conditionals -> jump & jump if not true

variables -> binding, SET&GET, symbol table in VM

loops -> if & jump

expressions

Program

a set of instructions

code

data

Process

the OS abstraction for a running program, PID

thread is a process with a shared address space

stack pointer SP

instruction pointer(program counter) PC or IP

address space

stack

heap

code

data

stack

return address

params

open files

local variables

heap

new()

malloc()

interpreter

tokenize

parse tokens to nodes

create AST, a tree of nodes

take a walk and eval

compiler

tokenize

parse tokens to nodes

create AST or another IR

emit bytecodes

VM

execute bytecodes

can be a stack or register machine

examples

java compiler vs jvm

c# compiler vs CLR

PVM

OS

bios

bootloader

kernel

user space

Kernel

virtual memory

file system

virtual cpu

Concurrency control

mutex

semaphore

Policies

Scheduling

Mechanisms

Process api

fork, exec, wait

signals

C

include

struct

typedef

union

enum

pointer

*p &p

atomic

volatile

const

static