administrivia using slides from here on out posted in advance as pdf on website exam back overall happy with results with some exceptions

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1 administrivia using slides from here on out posted in advance as pdf on website exam back overall happy with results with some exceptions short slides today gets to a good overview point probably a short class 1

2 course overview first part of course : second part of course : third part of course : 2

3 course overview first part of course : how computers interpret memory second part of course : third part of course : 2

4 course overview first part of course : how computers interpret memory second part of course : how computers remember third part of course : 2

5 course overview first part of course : how computers interpret memory second part of course : how computers remember third part of course : how computers compute 2

6 memory a computer remembers using memory but there are lots of kinds of memory each kind has different characteristics including speed, reliability, cost, power needs programs view the kinds differently and talk to them differently different kinds are arranged specifically to maximize usefulness 3

7 memory units usually measured in bytes (or multiples) usually abbreviated with capital B sometimes measured in bits (or multiples) abbreviated with lower case b kilobyte (KB) thousand (=1,024) bytes megabyte (MB) million (=1,048,576) bytes gigabyte (GB) billion (=1,073,741,824) bytes terabyte (TB) trillion (=1,099,511,627,776) petabyte (PB) quadrillion (=1.126x10 15 ) exabyte (XB) quintillion (=1.153x10 18 ) 4

8 timing units timing measured in seconds (s) or fractions of seconds millisecond (ms) thousandth (.001) second microsecond (µs) millionth ( ) second nanosecond (ns) billionth ( ) second picosecond (ps) trillionth (1x10-12 ) femtosecond (fs) quadrillionth (1x10-15 ) fast is relative to CPU can do adds every nanosecond 5

9 kinds of memory register scratch memory for computing part of cpu tens to hundreds of bytes very fast (< 300 ps to read or write) referenced by name can be accessed 1 to 64 bits at a time forgets as soon as power goes off very expensive per byte 6

10 kinds of memory RAM random access memory main memory in your computer now typically measured in GB also called DRAM D for dynamic (or dumb) moderate speed (70 ns to read) referenced by byte address typically 16 or more bytes at a time forgets soon after power goes off cheap per byte 7

11 kinds of memory cache memory extra memory to speed up your computer now typically measured in KB or MB also called SRAM S for static (or smart) reasonably fast (2-20 ns to read) referenced by byte address typically 16 or more bytes at a time may retain memory for several minutes w/o power moderately priced per byte 8

12 kinds of memory disk memory long term storage memory for your computer now typically measured in GB or TB slow (~10 ms to read or write) referenced by block address typically bytes (1 block) at a time retains data indefinitely 9

13 kinds of memory flash memory long term storage memory for your computer now typically measured in GB relatively slow to read (~2-5 ms) slower to write (~50 ms) referenced by block address typically bytes (1 block) at a time retains data for long time limited number of writes 10

14 memory hierarchy kinds of memory arranged specially from smallest at top (with cpu) fastest at top most accesses go to fastest memory fewer as farther away from cpu 11

15 memory hierarchy typical arrangement 48 bytes regs 12

16 memory hierarchy typical arrangement 48 bytes 64 KB regs L1 cache 12

17 memory hierarchy typical arrangement 48 bytes 64 KB 512 KB regs L1 cache L2 cache 12

18 memory hierarchy typical arrangement 48 bytes 64 KB 512 KB 2 MB regs L1 cache L2 cache L3 cache 12

19 memory hierarchy typical arrangement 48 bytes 64 KB 512 KB 2 MB 2 GB regs L1 cache L2 cache L3 cache DRAM 12

20 memory hierarchy typical arrangement 48 bytes 64 KB 512 KB 2 MB 2 GB 500 GB regs L1 cache L2 cache L3 cache DRAM Disk 12

21 caching memory only fast if cached some machines can only read from cache lots of different ways of finding things in cache of deciding what is in cache of updating cache caching behavior is very important usually more important than clock speed 13

22 virtual memory normal program sees little of this sees registers sees big array of bytes for memory sees disk (but only for files) this big array is actually virtual memory each program sees own 4GB of virtual memory 14

23 paging most of program memory on disk not enough RAM for everyone must be in RAM to be accessed moving from disk to RAM called paging bad paging can destroy computer performance we ll look at code that does that 15

24 disk arrangement multiple disks can be arranged specially to get better performance to get better reliability to get both called RAID striping mirroring full RAID 16

25 busses busses communicate between layers carry data also between computer and devices lots of busses in use as many as 10 busses on a typical computer all different flavors/sizes/capacities/uses 17