Lecture 01

History & System Overview

Before we open the hood, let's understand what the Apple II was, why it mattered, and what the major parts of the machine are. By the end of this lecture you'll be able to name every block in the system diagram and explain what it does.

1. A computer for people, not engineers

In 1976, "personal computer" meant a kit: a bag of chips, a soldering iron, and a front panel of toggle switches. Steve Wozniak's Apple I was a step up — a fully assembled board — but you still had to supply your own case, keyboard, power supply, and display.

The Apple II, introduced in April 1977 at the West Coast Computer Faire, changed the recipe. It came in a friendly plastic case with a built-in keyboard. You plugged it into a television, switched it on, and it was ready: a BASIC interpreter sat in ROM, waiting at a blinking cursor. It had color graphics and sound when its rivals (the Commodore PET and Tandy TRS-80, launched the same year — together the "1977 trinity") were monochrome and mute.

Nearly everything clever in the machine came from Wozniak's obsession with doing more with fewer chips. The floppy disk controller (1978's Disk II) used a handful of chips where rivals used dozens. The video system generated color essentially for free by exploiting quirks of the NTSC television standard. This minimalism is why the Apple II is such a good teaching machine: there is very little hardware, and every piece of it is understandable.

2. The family tree

This course targets the common core shared by all of them — what you'd find on an Apple II Plus or IIe, which is also what every emulator gives you by default.

3. What's in the box

Here is the whole machine at block level. Everything in this course lives somewhere on this diagram.

The cast of characters

• 6502 CPU — an 8-bit processor made by MOS Technology, running at about 1.023 MHz. It is the only "brain"; everything else is passive until the CPU touches it. Lecture 02 is all about it.
• RAM — from 4K to 48K on the original II. Your programs, your variables, and the screen contents all live here. The video hardware reads the same RAM the CPU writes.
• ROM — 12K of permanent memory at the top of the address space holding Applesoft BASIC and the Monitor (a tiny built-in debugger). The machine boots instantly because its "operating system" is already in ROM.
• Video generator — scans a region of RAM 60 times a second and turns it into a TV picture. Change a byte in that region and the character on screen changes on the next scan. No drawing API required.
• Built-in I/O — a keyboard, a one-bit speaker, game paddle inputs, and cassette ports, each controlled by touching special addresses (Lecture 03).
• Eight expansion slots — Woz insisted on them (Steve Jobs wanted two). They made the Apple II an open platform: disk controllers, printer cards, 80-column cards, memory cards, even CP/M co-processor cards.

4. Powering on: what actually happens

When you flip the switch on an Apple II Plus:

1. The 6502 comes out of reset and reads a reset vector — two bytes at addresses $FFFC–$FFFD, which are in ROM. They point to the Monitor's startup code.
2. The Monitor initializes the hardware, clears the screen, and (with no disk controller present) jumps into Applesoft BASIC.
3. BASIC prints its prompt, ], and blinks the cursor. Total elapsed time: well under a second.

If a Disk II controller card is in slot 6, its own small ROM takes over first and boots from the floppy — that's the famous whir-and-clatter of an Apple II starting up.

APPLE ][

]█

5. Why the Apple II still matters for learning

• The whole machine fits in your head. 64K of addresses, one CPU, ~90 instructions. You can know all of it.
• Nothing is hidden. No memory protection, no drivers, no OS. When you POKE a byte into screen memory, you are doing exactly what a game did in 1983.
• Instant feedback. Power-on to programming prompt in under a second. The distance between an idea and pixels on screen is one line of BASIC.
• The concepts transfer. Buses, address decoding, memory-mapped I/O, interrupts, stacks — every modern computer still works this way, just with more layers on top.

PRINT "HELLO FROM 1977"

Check your understanding