1 - represents the presence of a voltage in a circuit
0 - represents the lack of a voltage in a circuit

binary - is a base-2 numeral system.

Fun Fact 01 - All odd numbers have the lowest bit set to 1

source code -> compiler -> object files -> linker -> binary

There are three types of segments - is used for initialized data.

• .text
• .bss block sorted by symbol - uninitialized data
• .data

• .text - is mapped as read-only.
• .bss and .data - are mapped as writable, reserved for global variables.
• .bss - contains uninitialized data
• .data - contains static initialized data.
• .text - holds the program instructions.

• stack - the stack is a contiguous area of physical memory for storing various parts of a binary.
  
• stack frame - a place on the stack that stores each function of a program.
• top of the stack - is lowest numerical address
• strings - variables defined with string are stored in global variables not the stack
• POP - take whatever’s on the stack and put it into a register.
• CALL - pushes the next instruction on the stack, changing the value stored in EIP
• MOV - move from register to register, and register to memory, and memory to register

• Registers

Registers - small volatile memory storage areas built into the processor.

• ESP extended stack pointer - points to the top of the stack. lowest numerical address
• FLAGS - special one bit registers.
• EAX - Stores function return values.
• EBX - base pointer to the data section.
• ECX - Counter for string and loop operations.
• EDX - I/O pointer

The 8086 was Intel’s first 16-bit CPU.

• Intel x86 CISC - Complex Instruction Set Computer
• ARM RISC - Reduced Instruction Set Computer

RISC generally has more registers

Little Endian - stores the lowest part of a number in the lowest part of the address space.

memory can only be addressed in multiples of the word size and is measured in bytes.
words - generally 4 bytes or 32 bits.
Every byte of memory in the computer has its own unique address.
code segment - an area of memory where machine instructions are stored.
ASLR - Address Space Layout Randomization

• Intel: destination <- source
• ATT: source -> destination

• movl %eax, location - moves data into a memory location
• movl location, %ebx - moves data into a register
• Placing the $ sign before a label name takes the memory address of the variable and not the value.

movl $location, %edi

• Instructions
  • NOP Null Operation - in Intel architecture is one byte long and translates to 0x90 in machine code.
  • CMP is actually a subtract SUB of two values.

😮 Only 14 assembly instructions account for 90% of code.

The one byte NOP instruction is an alias mnemonic for the XCHG EAX, EAX instruction.

protected mode OS - divides the memory in user and kernel space.

goto in C translates to JMP in assembly.

• check and see if ELF stands for executing linking file