### Lecture 2: Trends; Introduction to Logic Design

#### Technology Trends

We continue to learn, at a steady pace, how to fabricate smaller and smaller transistors. This allows for

• a higher level of integration (currently, millions of gates on a chip)
• faster circuits (compare the initial PC of 5 Mhz with current PCs of 200 Mhz)

The cost of a chip has remained (very roughly) constant, so price/performance has been rapidly decreasing. How should this extra circuitry and extra performance be used? We shall return to this issue after discussing processor design.

### Logic Design: Combinatorial Circuits

(Text: Appendix B.2 and B.3)

#### Combinational circuits and gates

combinational circuits: no memory -- output is only a function of current inputs

gates are basic combinational circuits: AND gate, OR gate, inverter (complement), etc.

realization of gates from switches:

• OR gate from parallel circuit
• AND gate from series circuit

#### Representation of combinational circuits

• by Boolean formulas
• by truth tables
• by logic diagrams
• translating between these representations

#### Examples of combinational circuits

• NAND and NOR gates