Memory types

• Memory is separated by speed (fast -> small but expensive, large -> vice versa)
  • Registers
  • L1 Cache
  • L2 Cache
  • L3 Cache
  • RAM
  • SSD
  • HDD
• Cache locality
  • Temporal:
    • Recently accessed memory is likely to be reaccessed (loops & more)
  • Spatial:
    • If you access memory, you're likely to access nearby memory
• Cache lines
  • When memory is accessed, an entire line is (64 bytes on most x86)
  • Cache miss:
    • When you don't advantage temporal/spacial locality, access takes longer
    • Occurs on the first access, always (cache starts as empty)

Variable storage (Memory Alignment)

• Memory locations are based on data size (multiples of data size)
• Integers (Java -> 4 Bytes)
  • 0x1000, 0x1004, 0x1008, etc
• Longs (Java -> 8 Bytes)
  • 0x1000, 0x1008, 0x1010, etc. (Remember, addresses are hex)
• Misaligned data cause issues
  • CPUs read memory in chunks ()
  • Misaligned data can require two reads
  • Can cause craching