Outline

• Using Slidy
• The Memory Hierarchy
• Data Set Sizes

Using Slidy

• The slides for this class are HTML files.
• They are made to look like slides using a Javascript called Slidy.
• The following keystrokes do useful things in Slidy:
  • h - help (see all the commands)
  • f - fullscreen (gets rid of the links at the bottom of the window
  • space - advance a slide
  • left/right arrows - forward or back a slide
  • up/down arrows - scroll within a slide
  • a - show all slides at once for printing

The Memory Hierarchy: How Computer Memory Is Organized

• The fastest kind of memory could is actually below the cache in the above diagram and consists of the registers of the CPU. Usually, one has between 8 to 64 registers and these register range from 8bits to 64bits. These registers can be accessed at close to the clock speed of the CPU, so on modern machines on the order of a nanosecond (`10^{-9}S` to `10^{-10}`S) or slightly faster.

Cache

• The cache is part of the computer's microprocessor.
• It is capable of holding both data and instructions.
• The cache though only has limited memory.
• Sometimes cache changes are not immediately reflected in main memory.
• A cache might have up to four levels: an on-board L1 cache on the microprocessor, and levels L2, L3, and L4 which might be either on-board or in a different chip.
• Cache memory takes on the order of nanoseconds to tens of nanoseconds to access.
• As an example, the Intel's top-of-the-line 13th generation Core i9-13900KS Raptor Lake processor (2022) uses a 7nm process, have 8 performance cores and 16 energy efficient cores, each core has 80 KB L1 cache, the performance codes 1.25MB of L2 cache and the energy efficient ones 2MB of L2 cache, and it has a total 30MB L3 cache.
• Main memory look up is an order of magnitude slower than cache memory look up.

Main Memory

• Nowadays, new PCs have between 8GB to 128GB of main memory.
• A bit of memory can store a single binary digit. I.e., can hold either a 0 or a 1. A bit of of memory is abbreviated by a lowercase letter b.
• A byte can hold 8 bits. A byte of of memory is abbreviated by a uppercase letter B.
• For larger amounts of memory, either metric or a power of 2 notation is used.
• Metric prefixes like kilo-, mega-, giga-, etc., we write with their standard initials k, M, G, etc.
• Corresponding to each of these metrics, we have a corresponding base 2 prefix: kibi- (`2^{10}`), megi- (`2^{20}`), gigi- (`2^{30}`), etc., which we abbreviate as Ki, Mi, Gi, etc.
• Putting the above together, we can make the following memory table:

  Metric	Power 2
  1KB (or 1kB) (one kilobyte) = 1,000B	1KiB =`2^{10}`B = 1024B
  1MB = 1,000,000B	1MiB =`2^{20}`B = 1024KiB
  1GB = `10^{9}`B	1GiB =`2^{30}`B = 1024MiB
  1TB (one terabyte) = `10^{12}`B	1TiB =`2^{40}`B = 1024GiB
  1PB (one petabyte) = `10^{15}`B	1PiB =`2^{50}`B = 1024TiB
  1EB (one exabyte) = `10^{18}`B	1EiB =`2^{60}`B = 1024PiB

• Moore's law says the number of transisters in an integrated circuit that can be packed into the same size package doubles roughly every two years.
• Physics will eventually prevent this law from continuing indefinitely (we're probably close to its end), although it has held for more than 50 years.

Example Database/Data Set Sizes