Bits and bytes

What is a Bit?

A bit is the smallest unit of data in a computer and can have one of two values: 0 or 1.

Think of a bit like a light switch that can be either off (0) or on (1).

What is a byte?

A byte is a group of 8 bits. It’s the standard unit of data used to represent a single character in memory. Since each bit can be either 0 or 1, a byte can have 2^8 (256) possible values, ranging from 0 to 255

Assignment

What is the 11001010 converted to a decimals ?

• Answer
  • 2^7: 1×27=1×128=128
  • 2^6: 1×26=1×64=64
  • 2^5: 0×25=0×32=0
  • 2^4: 0×24=0×16=0
  • 2^3: 1×23=1×8=8
  • 2^2: 0×22=0×4=0
  • 2^1: 1×21=1×2=2
  • 2^0: 0×20=0×1=0 = 202

Representing bits and bytes in JS

• Bit

const x = 0;
console.log(x);

• Byte

const x = 202
console.log(x);

• Array of bytes

const bytes = [202, 244, 1, 23]
console.log(bytes);

UInt8Array

A better way to represent an array of bytes is to use a UInt8Array in JS

let bytes = new Uint8Array([0, 255, 127, 128]);
console.log(bytes)

Why use UInt8Array over native arrays ?

• They use less space. Every number takes 64 bits (8 bytes). But every value in a UInt8Array takes 1 byte.
• UInt8Array Enforces constraints - It makes sure every element doesn’t exceed 255.

Assignment -

What do you think happens to the first element here? Does it throw an error?

let uint8Arr = new Uint8Array([0, 255, 127, 128]);
uint8Arr[1] = 300;