What is a head ?

[James S. <jsi...@ac...>]

Hi everyone!!!

   Okay I was hoping for more response or ideas. Their seems to be much
confusion on what a head is and how to handle it properly in Linux. The
confusion comes out of not knowing what we really need done and what
things like a head are. It's hard to think of it off the top of your head.  
I have thought about it and realized the wway to look at it is from a
historical view point.

  Before the day of the PCs the computer industry was dominiated by
mainframes. They where huge massive machines that filled up a room.
Most often people didn't actually work in these rooms but in
seperate locations. People needed a way to access them. So something
called a tty was developed. A device that had a keybaord and a text
display built together. Many of devices where attached to the mainframes.
This allowed many employees to work at the same time on these mainframes.
So in essence we had the first multiheaded systems. Each tty became know
as a terminal. 
  Then the PC entered the market and as you know ended up pushing the
mainframes into a smaller market. The PC had a different design goal. It 
was a machine designed to be used by a single person. No one else could
attach themselves to you machine. Then companies needed these PC to talk
to each other but yet retain the local machine idea. A attempt to retain 
the old mainframe way of doing things. So you seen local networkes emerge
in offices. As time went on PCs now have shifted the design goal. They
now are becoming more multimedia oriented. So now you seen the developement 
of things like joysticks and soundcards etc. 
  Now in recent times technology has emerged that allows more than one of
the same type of device be attached to a PC. You could have a PS/2 mouse
and a serial mosue attached at the same time. The trend amplified even
more. Now with PCI bus you can have multiple video cards running in the
same PC. So now you can have the PC itself behave just like the old
mainframes used to. Today the term is called multihead. It's still the
same thing with the old mainframes. You can have mor ethan one person now
working on the same machine directly. The difference being the PC is much
smaller and cheaper then the old mainframes used to be. The other
difference is the PC has much greater variety of types of hardware you can
attached. The old mainframes just had the ttys. 
  So you can see that in the days of mainframes multihead was done with
ttys and their didn't exist the extra devices like their is today. So now
we have migrated from a terminal to a head. What is the difference? Well a
head can be though of as a extenstion of a terminal or better yet a
terminal is a subset of a head. So a head is a place where a person can
sit down and interface with a machine. The person experiences the
virtual computer. The computer seems to belong to just him or her. You
have a bunch of input devices that can manipulated by a single user and
have a effect on what he/she experiences (usually a video screen). A
terminal can now be one of these devices alongside other devices such as
joysticks. Now that we know what a head is the next question is what makes
a device belong to a head? A device belonging to a head means that data
goes from the devices attached to that head to be displayed on a device
attached to that head. In plain english what you do doesn't end up on
someone elses head. You don't move someone else cursor or display your
text on their screen. Now we have different types of devices that can be
attached to a head. A input device or a output device or a device that
does both. A input device would be a mouse. A output device would be a
video card or a sound card. A device that does both would be a serial or
video terminal. Also a device can behave as different types of devices. A
sound card for example. You might want to have different sound card belong
to different heads or you might have one sound card and have that piped
into the entire office. So these are things to think about when it comes
to the design of this new system.  

"Look it's a text editor, no it's a OS, no it's Emacs"
James Simmons                                           ____/| 
fbdev/gfx developer                                     \ o.O| 
http://www.linux-fbdev.org                               =(_)= 
http://linuxgfx.sourceforge.net                            U