October 2001
Computing for the Bewildered. By Bill Hayles
Hello again.
Do you remember that in August I was asked
"What is Windows?"
I decided to answer the question in two sections. This month, we'll
look at how Windows (or any operating system) controls your computer
hardware. Some of what we explore is true for any operating system, but
much is specific to Windows 95, 98 or ME, as I know they're by far the
most commonly used versions at present.
Why do we need an operating system at all? It's because the computer's
CPU is essentially dumb. It knows how to do things, but not when to do
them or co-ordinate them. When you boot (start up) your computer, the
first thing it does is to check it's in working order. Some details of
your system are stored in a chip called the BIOS. The CPU checks that
the devices it can communicate with are the same as those stored in the
BIOS (this is called the POST - Power On Self Test). The BIOS then
tells the CPU to look in a certain place, usually the beginning of the
first hard disk, to find out what to do next. This is where the
operating system takes over.
If there were no operating systems, every piece of software would have
to access the CPU directly, and, what is more, you could only have one
such application per disk. Indeed, in the very early days of the PC
(I'm talking about 1983 to 1985), there were applications that included
their own operating system, and operated in isolation from everything
else, needing a reboot both to load and unload. But those days are
long gone. An operating system has an API, an Application Programming
Interface. Those who are writing software don't reinvent the wheel,
they make use of the Windows API and write their program to interface
with Windows, leaving it to access the hardware on the program's behalf.
So, what happens when the CPU reads the "boot sector" on the disk? Windows
starts to load program code from hard disk to memory. Firstly, it loads
a copy of DOS. DOS was the original Microsoft operating system for the
PC, and is still the basis of Windows (but not the new Windows XP).
Next, it loads drivers (small pieces of code that remain in memory all
the time the system is running) that enable it to interface with the
specific hardware of your system (your video and sound systems, for
example). Incidentally, before doing so, it runs a check that the
hardware it encounters has not changed. If it finds a new item of
hardware, it stops, announces the fact, and invites the user to install
the necessary drivers to use the hardware.
Having done that, it starts to load all the pieces of code necessary to
enable other software (programs) to access the hardware, including the
registry which is where individual programs often store configuration
details. Finally, what is correctly called the shell is loaded. This
is the interface of Windows to the outside world, (i.e. you, the
operator), and is more usually called the desktop. Finally, any
programs that you have instructed Windows to start at boot time (by
having short cuts to them in the startup folder) will be started. Once
these are loaded, the computer is ready for work.
Now you can dial-up and collect your e-mail using Becky, browse the web
using Opera, write a novel with Star Office or even play Transport
Tycoon. The uses to which computers can be put are as diverse as those
who operate them. But they will have one thing in common. They will
use the operating system as a "translator" between themselves and the
hardware.
It is important to distinguish between Windows, the operating system,
and applications, or programs that run under it. These applications
may well be from Microsoft, and may also have come packaged with
Windows and be on the installation disk, but they are not necessary for
the operation of Windows, the operating system. They range from small
frivolities like Freecell to major applications such as Internet
Explorer and Outlook Express. The reason I emphasise this is that when
you have a problem, and you ask for help, whoever is helping you needs
to pinpoint the source of the problem. When they ask "what application
does it occur in?", the answer is NOT "Windows"! "Microsoft Outlook
Express version 5 under Windows 98 Second Edition" may be the counsel
of perfection, but the more detail the better. Help your helper to help
you.
That's all for this month. My Saturday morning classes are every
fortnight at 1030 at The Oasis Centre. Dates in October are the 13th
and 27th. All are welcome. Details will be on the Internet at
http://www.billnot.com, but seeing as how you probably don't know how
to get on line some notes etc are available at the CopiShop (depending
on how many we have left over.
I don't yet know what I'll be discussing next month, so If you have a
question you'd like me to answer in the column, please e-mail it to
questions@billnot.com, If you don't have e-mail, you can
always leave your question at the CopiShop. However, I can't guarantee
to answer questions personally.
If you have been, thanks for reading this.