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PC's are so powerful today that just one PC can often support
several persons using it at once, especially if they are doing
low-load tasks such as text editing, data entry, etc. One way to do
this is to connect a number of terminals to a single PC (or other host
computer) by modems or direct cable connection. To do this, it's
usually best to have a multi-user operating system such as Linux so
that each user at a terminal can use the computer independently. This
has been called "time sharing" but it's not good terminology today
since "distributed" computing over a network is also a type of time
sharing. It might be better described as "centralized" computing.
But the central computer may be connected to the rest of the world via
a network so that terminal users may send email, browse the Internet
with the lynx browser, etc. So it's not exactly "centralized"
either.
Terminals have seldom been used with PC's because the popular
operating systems used for them (Windows, DOS, and Mac) were not
multiuser until 1998 (available for MS Windows NT) and previously
could not support terminals very well. Now that Linux, a multiuser
operating system, is freely available for PC's, the use of terminals
with PC's becomes more feasible. The drawback is that text terminals
are not smart enough to support the type of graphical user interface
(GUI) that many computer users today normally expect.
When Computers (including PCs) were quite expensive, lower hardware
costs was a significant advantage of using terminals. Today with
cheap PCs, the cost savings is problematical. Here's what I wrote
years ago when PCs were more expensive. It's still true today but of
less significance.
If several people use the same computer as the same time, there is a
reduction in the amount of hardware needed for the same level of
service. One type of savings is due to code sharing. The application
files on hard disks are shared as well as shared libraries in memory
(even when people are running different programs provided they use
some of the same functions in their code). Another type of savings is
due to reduction of peak load. The hardware of a single PC may be
idle most of the time as people slowly type in information, think,
talk, or are away from their desks. Having several people on the same
computer at once makes good use of much of this idle time which would
otherwise be wasted.
These savings are substantial. One may roughly estimate (using
statistical theory) that for 9 persons (8 terminals & 1 console) the
shared PC only needs only about 3 times as much capacity (in memory,
disk storage, CPU power, etc.) as a single PC in order to provide the
same level of service per person. Thus the computational hardware for
such a shared system should only cost about 1/3 as much per user.
However, the cost of the display hardware (CRT's, keyboards, video
electronics, etc.) is about the same for both cases. The terminals
have the added cost of requiring additional serial ports at the host
computer.
For a fair comparison with PC's, the terminals should have the same
capabilities as the PC monitors. Unfortunately, color graphic
terminals for Linux (X Window) with high speed communication cost
about as much as a PC so in this case there not much (if any)
savings in hardware costs. But for text terminals there will be some
savings, especially if the terminals are obtained used at low cost.
For centralized computing, software (and the updates to software)
only need be installed and configured on one host computer instead of
several. The person in charge of this computer may control and
configure the software which is installed on it. This is advantageous
if the person controlling the host computer does an excellent job and
knows about the needs and preferences of the other users. Users can
be restricted in playing games or surfing the Internet by not
installing the software (or by otherwise restricting access to it).
Whether or not centralized control is desirable depends on the
situation.
With terminals, the computer hardware upgrades take place on only
one computer instead of many. This saves installation labor effort.
While the cost of the hardware for the host computer upgrade will be
more than that for a single PC (since the host needs more computing
power than a PC), the cost will be significantly less than upgrading
the hardware of a number of PC's being used instead of terminals.
- The elimination of noise from fans and disk drives (unless
you're using a PC to emulate a terminal).
- The users of the terminals can share data and files
and send e-mail to each other. It's similar to a local network.
- Text terminals have no high-speed graphic display (or high
resolution graphics) although they can often use graphic character
sets to draw boxes, etc. This lack limits the software that may be
used on it.
- If the host computer goes down, then no one can use the
terminals either (unless there is a "standby" host computer to connect to).
Text terminals are technologically obsolete because for a slightly
higher cost of hardware, one could build a smarter terminal (with the
same quality of display). This wasn't always the case since around
1980 memory cost thousands of dollars per megabyte. Today with low
costs for memory and processors, one could turn a text terminal into a
GUI graphic terminal for only about a 10% or 20% increase in hardware
cost. Since a PC can emulate a terminal, almost everyone using
computers has a terminal emulator available.
The reasons that text terminals are not fully obsolete are:
- The resolution of characters on the screen is better on
monochrome terminals than for monitors in text mode.
- Many people don't need full screen graphics.
- Since running a text-terminal (in contrast to a GUI-graphics
terminal) doesn't consume much of a modern PC's resources, a large
number of terminals may be efficiently run from one PC.
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