Apple IIe - Manual (Page 23)

Page 23 of 74 IIe
Printed: Tuesday, March 4, 2003 10:40:15 AM
in a language similar to English. An interpreter program, also in ROM, then translates those
English-like terms into machine language a binary code of zeros and ones that is the only
language the microprocessor can really understand.
Other Languages:
There are other programming languages you can use with the Apple IIe (Logo and Pascal, for
example), but they aren't stored in ROM.
You have to load them into RAM from disks before you
can write programs (the same way you have to load application programs into RAM before you can
use them).
How It Works
Armed with this rudimentary knowledge of what RAM, ROM, and the microprocessor do, you'll be
able to understand how programs are loaded into memory from disks, and how the information you
create while using a program is saved on and retrieved from disks.
You don't need to know
everything about how the computer works to run programs successfully anymore than you need to
know how an internal combustion engine works to drive a car but you'll use your computer with
greater confidence and creativity once you have a feel for how programs and data move through
the computer system.
Starting Up
The first thing that happens when you flip the Apple IIe power switch is that a program in ROM
tells the microprocessor to check drive 1 for a disk with an operating system.
An operating
system is a set of instructions that tell the computer how to work with the information on
disks. Because the operating system controls the way information is retrieved from and stored
on disks, it is also called a disk operating system.
Once the operating system is in RAM, the operating system tells the microprocessor to load the
application program into RAM.
Once that happens, the computer takes on its personality as a
Spanish teacher, a financial planner, or an arcade game, depending on what kind of program disk
you have in drive 1.
Two-Stage Startup:
Some programs, like AppleWorks, are too big to fit on one disk, so they come on two disks. The
first disk, usually labeled the Startup or Boot disk, contains the operating system. The
second disk, usually labeled the Program disk, contains the program. Starting up a two-disk
program is called a two-stage boot or a two-stage startup. To execute a two-stage startup, all
you do is put the startup disk in drive 1 and turn on the computer. A message on the screen
will tell you to exchange the program disk for the startup disk and to press some key (usually
Return) to start using the program.
Creating Something From Scratch
At this point, you start creating your letter or your budget, and everything you type (your
data) is stored in RAM.
Saving Data
It's important for you to remember that the information stored in RAM is only stored
temporarily.
Before you turn off the computer or switch to another program, you must save your
work (data) on a disk. When you save your work on a disk, it's called a file, and you give it
a filename by which you'll be able to retrieve it later.