# Introduction

Tom Kelliher, CS 240

Jan. 25, 2012

### Outline

1. Syllabus.

2. Big picture: architecture of a PC.

3. Tiny picture: current, voltage, etc.

### Coming Up

Binary logic, gates, Boolean algebra.

# Big Picture

Block diagram of a PC, centered on system bus chip.

Include: keyboard, mouse, monitor, disk, CD, modem, network card, sound.

Terms (define): ISA, PCI, AGP, PCI-X, PCI Express, USB, SATA front side, etc. MHz, bandwidth, b, B, etc.

Why so many buses?

# Electrical Level Considerations

Why are computers digital?

What number system do they use?

Consider a circuit containing a power source, a resistor, and a capacitor, all in parallel.

1. Voltage.

2. Current.

3. Capacitance.

4. Resistance.

How do we represent 0 and 1? Voltage. Or current.

Logic levels for SN7400 5 V part (see class home page for data sheet):

1. VoH: 2.4 V min

2. VoL: 0.4 V max

3. ViH: 2.0 V min

4. ViL: 0.8 V max
Why the discrepancy on input/output voltages?

Example: 7400 two-input NAND gate waveform. Note voltage vs. time.

Why is digital logic binary?

Thomas P. Kelliher 2012-01-23
Tom Kelliher