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Status: Tags: Links: Nand2Tetris Unit 3

Data Memory

Part of the HACK Computer

Principles

Worth vs value of a bit ?

• Worth is the potential, what it represents, while value is the current value in relation to worth

Memory models (addressable) ?

• Word (only start of each register)
  • Texas instruments
• Memory size (can access any byte)
  • AMD chips

Types

• Main memory RAM

• Secondary memory (disks)

• Volatile (RAM) / Non-Volatile (Disks)

• Why only 0 and 1 in memory cell?

  • Voltage levels transmitted on noisy wires determine what number based on range
    • ex) 0.0 → 0.2v = 0, 0.9 → 1.1v = 1

• The width is the amount of data in a single register, and the adress is the location of a register within a larger chip

Ordering

• Most significant byte is left hand side as it dictates larger digit

• Least significant byte is right hand side as it represents smaller number

• Little endian

  • start at higher address and work down
  • Little end as it finishes reading at the lower address

• Big endian

  • Start at lower address and work up

• Left shift

  • x « y
  • Shift bit vector x left y position
  • Fill right with 0

• Right shift

  • x » y
  • Shift bit x right y positions
    • Logical shift, fill left with 0
    • Arithmetic shift, move lsb to msb

Tiers

References: