Download But How Do It Know? - The Basic Principles of Computers for Everyone PDF

TitleBut How Do It Know? - The Basic Principles of Computers for Everyone
Tags Basics Of Computer Basic Computer
File Size4.4 MB
Total Pages205
Table of Contents
                            Front Cover
Just the Facts Ma'am
Just a Little Bit
What the...?
Simple Variations
Remember When
What Can We Do With A Bit?
A Rose by Any Other Name
Eight Is Enough
Back to the Byte
The Magic Bus
More Gate Combinations
First Half of the Computer
The Other Half of the Computer
More Gates
Messing with Bytes
The Left and Right Shifters
The NOTter
The ANDer
The ORer
The Exclusive ORer
The Adder
The Comparator and Zero
The Arithmetic and Logic Unit
More of the Processor
The Clock
Doing Something Useful
Step by Step
Everything's Under Control
Doing Something Useful, Revisited
What's Next?
The First Great Invention
The Arithmetic or Logic Instruction
The Load and Store Instructions
The Data Instruction
The Second Great Invention
Another Way to Jump
The Third Great Invention
The Clear Flags Instruction
Ta Daa!
A Few More Words on Arithmetic
The Outside World
The Keyboard
The Display Screen
Another Code
The Final Word on Codes
The Disk
Excuse Me Ma'am
That's All Folks
Hardware and Software
The Operating System
The File System
Computer Diseases?
Digital vs. Analog
I Lied - Sort of
Full Disclosure
Document Text Contents
Page 2


The Basic Principles of Computers For Everyone


J. Clark Scott

Page 102

The wiring for this operation is simpler than the other one, just two enables and
two sets.

There are many combinations of things that we can do with the RAM, the six
registers and the ALU. We could get a byte from RAM and move it to any of the
four registers, we could move any one or two of the registers through the ALU
and ADD them, AND them, OR them, XOR them, etc.

We need a way for our CPU to do one thing one time, and a different thing the
next time. The control section needs something to tell it what to do in each

Page 103


Now here's a scary idea. Imagine that the job that an employee does at a fast
food restaurant gets broken down into its individual elements. Walk to the
counter, say "May I take your order?" listen to the answer, press the
"cheeseburger" button on the cash register, Now lets say that there are 256 or
less individual actions involved in the job of working at such an establishment.
You could then invent a code that would associate one of the states of a byte with
each of the individual activities of an employee. Then you could express the
sequence of an employee's actions as a sequence of bytes.

First we make up a code table. We write some codes down the left side of the
page. Then we decide what we want those codes to mean, and write those
meanings next to the codes. Now we have a list of all of the possible actions that
an employee might take, and a code that represents each one of them:

0000 0000 = Walk to the counter

0000 0001 = Say "May I take your order?"

0000 0010 = Listen to the answer

0000 0011 = Press the cheeseburger button

0000 0100 = Press the fries button.

0000 0101 = Press the milk button

0000 0110 = Press the total button

0000 0111= Collect the money

0000 1000 = Give the customer the change

0000 1001 = Open an empty bag

0000 1010 = Place a cheeseburger in the bag

0000 1011= Place fries in the bag

0000 1100 = Place a milk container in the bag

0000 1101= Hand the bag to the customer

1000 0000 = Go to the step number in the right 6 bits.

0100 0000 = If "yes," go to the step number in the right 6 bits.

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