1. CPU caches
    1. Computers now have L1, L2, L3 caches. 8-core chip has L1 for each core, one L2 for each 2 cores,  and L3 cache shared by all cores.
    2. L1 (8, 16, 32, .. 128 KB) core speed – stack cache is usually in L1
    3. L2 (256,… 1024 KB) – 1/4 or 1/2 core speed, when L1 cache is full it spills to L2. L3 usually half of L2 speed, not all computer chips have L3.
    4. The way it works is: RAM caches the hard-disk, L2 caches the RAM, L1 caches L2.
  2. iPhones CPU:
    1. iPhone 3GS: 600 MHz ARM-Cortex A8 (32-bit)
    2. iPhone 4: Apple A4 processor = ARM-Cortex A8 (CPU) +  PowerVR GPU
    3. iPhone 4S: Apple A5 processor = dual-core ARM-Cortex A9 (CPU) + dual-core PowerVR GPU
    4. iPhone 5: Apple A6 processor = dual-core ARMv7 + triple-core PowerVR GPU
    5. iPhone 5S: Apple A7 processor (64-bit) = dual-core ARMv8 (CPU) + 4-core GPU,
  3. Hard-disks: Flash drive SSD vs HD:
    1. HD: actually mechanical, spinning disk.
    2. SSD (Solid State Drive): SSD has no moving mechanical part -> quicker, silent, physically durable but 10 times more expensive than HD
    3. SSD has limited write times, but with current technology even if written 3times/ day (a lot) , it can last 25 years.
  4. RAM:
    1. SDRAM: (Synchronously RAM) transfer rate = clock rate.
    2. DDRAM: (Double speed of SDRAM) transfer rate = 2 x clock rate.
    3. DDR2: double speed of DDRAM
    4. DDR3: double speed of DDR2 
  5. 32-bit system vs 64-bit system:
    1. The size of data-bus of RAM dictates if the system is 32-bit
    2. 64-bit system has:
      1. 64-bit CPU
      2. 64-bit databus
      3. 64-bit address bus