Class 3		W   1/16	Comp 110

3 building blocks of every computer
  CPU - central processing unit
  Main memory  (= RAM)
  Disk (= hard drive) 


CPU		MM		Disk
-------------------------------------
active		passive		passive
runs programs   program & data
 		program running

		volatile	non-volatile
very fast	200x slower	1,000,000x slower than MM   
                   than CPU 
4MB cache	4GB		1000GB
memory


Even slower than disk is a local Ethernet network where your
computer is attached by a cable to the network.  Wifi is much,
much slower than Ethernet. 


clock = drum beat of the computer
    everything that happens in the computer is syncrhonized
       with the clock
    typical clock speeds 2.0 GHz (laptop),  3.0 GHz (desktop)
    speed of computation directly proportional to clock speed

core = a separate computer located on the CPU chip
    Most computers today have 2 (or more) cores
    This means the computer can be running 2 programs at the same time.
        Potentially twice as fast.

cache = a very small amount of very fast memory
    Located on the CPU chip
    Temporary storage of the program and data that the CPU is currently
        using.
    When needed, main memory is copied into cache memory.
    When no longer needed, contents of cache memory copied back to main 
        memory
    Cache solves the problem of main memory being 200x slower than CPU


When buying a computer, the key determinants of its speed are
(in order of importance):
--- number of cores
--- clock speed
--- amount of cache memory on the CPU chip


Questions you need to be able to answer:
--- What role does heat play in computing?
--- Why are laptops slower than desktops?
--- Why is main memory so much slower than the CPU?
--- Why is a disk drive so enormously slower than main memory?


Link to animation of disk drive (#1-3 are useful visualizations)
http://www.research.ibm.com/research/demos/gmr/index.html

Link to microprocessor chip photo
www.cs.unc.edu/~hedlund/Images/microprocessor4core.jpg

Link to photo of a motherboard (printed circuit board)
www.cs.unc.edu/~hedlund/Images/pcBoard.jpg