Tom Kelliher, CS 240

Jan. 25, 2012




Read 2.1-2.


  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