Max Learning's Digital Dozen

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1. bit   2. Byte   3. Code   4. Data   5. Program   6. Chip   7. CPU   8. RAM   9. ROM   10. Computer   11. Peripheral   12. System

Wafer etched with Switches and circuitry.
Acronym: Ch = Wew-Sac (pronounced WUU-sak).

The theme is switches. And although switch technology has evolved over the decades from hand-operated toggle switches, to electromagnetic switches, to vacuum tubes, to transistors, in each case we're talking about using switches to receive and send messages.

Chips are fingernail-sized wafers of layered semiconductor materials etched with millions of microscopic switches and circuitry. They hold your data and instructions in the form of off/on patterns represented by 0s or 1s. Because a chip's surface combines, or integrates, various electronic components into one unit, chips are sometimes called integrated circuits or ICs.


Max. If a chip is only the size of my fingernail, how can it hold millions of switches?

I'm amazed myself, B.P. Here's a simplified description of how chips are made.
Making Chips

Most chips are made of silicon (SIL-ih-kawn), a natural semiconductor and one of the most abundant substances on earth. In fact, silicon is the primary component of beach sand. Trap: Avoid embarrassment, do NOT pronounce it silicone (SIL-ih-kohn), which is a totally different substance!

Semiconductors, unlike true conductors, reluctantly transmit electricity and can be switched Off and On with a remotely-sent electrical charge.

To start the chip-making process, grains of silicon are melted in high temperature furnaces and shaped into cylindrical ingots. After cooling, the ingots are sliced into thin circular wafers using a diamond-bladed saw. These wafers look metallic but are actually brittle and delicate, like glass. Once polished they shine like silvered mirrors.

The switches and circuitry for the chip start as several layers of hand- or computer-drawn lines and shapes which are optically reduced to a microscopic fraction of their original size. A "mask" is then created for each layer of circuitry.

The pure silicon wafer is coated with a silicon compound and a light-resistant material called photoresist. The first mask is attached and the assembly is exposed to ultraviolet light. Where light passes through the mask, it hardens the photoresist. The exposed wafer is then bathed in acid which eats away the nonhardened photoresist and etches the first layer of circuitry into the silicon compound.


After being recoated with more silicon compound, photoresist, and the second-layer mask, the wafer is re-exposed to ultraviolet light and another acid bath which etches the second layer of circuitry. This process is repeated perhaps dozens of times until all layers of circuitry are etched into the wafer.

A single wafer typically holds hundreds of chips which are then cut into individual pieces.

Protective Housing
Although chips appear to be metallic, they are more like glass in character, hence very brittle. For protection, each chip is mounted inside a plastic or ceramic housing. This housing looks like a square or rectangular bug with several metal legs sticking out. Tiny wires attach the chip's circuits to the metal pins. These pins then plug into the computer's circuit boards, putting the chip into contact with the rest of the computer.


The three major chip types are CPU, RAM, and ROM, and we'll cover each of these separately.


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