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Wednesday, December 7, 2011

The Woz's Early Exposure to Electronics

Here is what I was trying to --- hic-- say about Steve Wozniak --hic-- in Podcast #139:

From "Steve Jobs" by Walter Isaacson:

"One of Steve Wozniak's first memories was going to his father's workplace on a weekend and being shown electronic parts, with his dad "putting them on a table with me so that I could play with them." He watched with fascination as his father tried to get a waveform line on a video screen to stay flat so that so that he could show that one of his circuit designs was working properly. "I could see that whatever my dad was doing, it was important and good." Woz, as he was known even then, would ask about the resistors and transistors lying around the house, and his father would pull out a blackboard to explain what they did. "He would explain what a resistor was doing all the way back to atoms and electrons. He explained how resistors worked when I was in the second grade, not by equations, but by having me picture it."

This is clearly the approach to electronics that we see in the book "From Atoms to Amperes" by F.A. Wilson.

Mike, KC7IT, gave Woz a new title "the uber-knack-master of all time":

Woz is the uber-knack-master of all time, and always has been in my book. His Apple II design is a work of genius in getting ten pounds of function out of five pounds of parts.

One of many examples: Apple II was the first personal computer to use DRAM memory chips, which were brand new then and kinda scary even for us pros. DRAMs store data as charges on tiny leaky capacitors. Every 20 milliseconds or so they have to be refreshed.

Everyone else had counters and logic just for refresh. Woz arranged the Apple II's display memory, so reading out the pixels to the TV screen 60 times per second did the refresh too, at no cost in circuits or performance. The elegant design of a pure knack genius.

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1 comment:

  1. Thanks Bill! Here's another Woz wonder in the Apple II: color for nothing. Apple II's crystal is 14.318 MHz. Why this peculiar frequency? It's 4x the 3.579 MHz NTSC color subcarrier!

    In high-resolution graphics mode, Apple II shifts out pixels at this 14.318 MHz rate. Normally the display is black and white and they just look like very small pixels. To get color, Woz sends out 00110011001100... at the start of each line. Look at those bits visually, it's a 3.579 MHz waveform, the NTSC color burst!

    Now the TV sees the pixels as a color subcarrier! Remember NTSC encodes hue by phase-modulation. 0000 is black, 1111 is white, but 0011, 0110, 1100 or 1001 are different phase shifts on 3.579 MHz. Each phase shift shows up as a different color. That's how the Apple II did color for nothing.

    That's not all: sound, floppy disk, cassette and joystick interfaces all for next to nothing. It's here:

    Woz is the uber-knack-master of all time.


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