Elements of Computing Systems // 2: boolean arithmetic

Basic logic gates can be combined to create an ALU (arithmetic logic unit) which is the centerpiece of a CPU. Basic arithmetic is how low-level computing is carried out.

• All boolean arithmetic can be carried out by addition. Wha?
• Word size - number of bits a computer is using to represent a chunk of information, e.g. an integer
• Byte, short, int, long correspond to 8, 16, 32, 64 bit integers!
• Negative numbers represented by counting down from max (2 to power of n - m).This is called two’s complement or radix complement method. Has a few cool properties:
  • All negative start with 1 (In top half of range)
  • Addition of pos/neg can be done very easily with a cheap algorithm
• ALU will often only carry out a portion of arithmetic functions directly. Rest are often handled by OS