Educational program - Local computer networks.

 What should we build a network? 
                                
before we start talking about
local networks, you should
define the terminology.
As a rule, "computer networks"
for most people
are associated with some
abstract information
systems or in general
incomprehensible heaps
electronics mysterious
purpose.        Actually
It is generally accepted that networks are
two types: local, i.e.
connecting groups of computers
one or more
enterprises, andglobal,
connecting computers to
significant distances,
different cities or countries.  B
currently operational
many global networks,
providing communication via
telephone channels and satellite
communications.      Almost everything
global networks communicate with each other
with a friend through special
network nodes called
"gateways".   Having a modem, any
user PC can
connect to such a network.
The main difference between local networks
from global ones is that
what in the first case
special ones are laid
high-speed lines, while
time as in the second case
publicly available
low-speed communication channels,
usually rented from
relevant organizations.    
                                
 Types of local networks. 
                                
there are many types
local networks, however
greatest distribution
received three modifications:
Ethernet, Arcnet and Token-Ring.
Ethernet technology is the most
widespread due to
its reliability and high
data transfer rates.  This
technology was developed in
1975 by the company Xerox. At the beginning
80s company Digital Equipment,
Intel and Xerox unveiled
network specificationEthernet.
Ethernet based local network
operates on the principle "general
bus", which consists in
as follows: to connect to
network uses one cable, to
to which all network networks are connected
workstations.   Messages,
sent from one station to
other, accepted by everyone
other computers on the network.
When transferring data, it happens
signal filtering, in
resulting in a message
reaches the desired addressee.
If the network station needs
convey the message, she first
checks whether the line is busy or not:
transmission occurs only in
if the line is free.
Fairly high reliability
this method is due
independence of network operation from
operation of individual computers.   
   Relatively recently large
began to enjoy popularity
networks built on the basis of the method
Arcnet.   Surge of interestto
Arcnetwas caused by a sharp
reduction in prices for network
adapters of this architecture - in
as a result they became cheaper
Ethernet adapters.    Arcnet
works using topology
"Star". All network computers
connect to one common
device using separate cables.
Network reliability with such
organization is smaller than
Ethernet, because  when leaving
building a central device
all work stops
networks.   Connection is also possible
several Arcnet networks into one
large network with extensive
structure.    Data transfer
happens as follows:
one of the network workstations
generates a message
a certain type (marker),
which is transmitted from one
computer to another - and if
any computer wants
convey the message, then he just
adds it after the marker.
When the message gets through
destination station, it is deleted
from the list of transmitted
messages.ArchitectureToken-Ring,
developed by IBM,
provides interaction
network computers according to the scheme
"ring".  Messages are transmitted
from the first computer to
second, from second to third -
and further in order: if
current message is not
intended for this
computer, it is transmitted
to the next one, if the addressee
is the current computer,
the circular is removed from the list
messages.                      
                                
       Ethernet - hardware.       
                                
it is absolutely obvious that
any network inevitably includes
cable connecting workers
stations among themselves, and Ethernet
is no exception.
Ethernetcan work with three
cable types: thick
coaxial, thincoaxial and twisted pair.  B
depending on cable type
changes quite significantly
list of required hardware
provision and characteristics
networks.   Of course, for work
network, regardless of cable type
network cards required
inserted directly into
expansion slots on motherboard
computer board.    Fat
coaxial cable, or whatever
it is sometimes called "yellow"
(by shell color), is
the most expensive. "Yellow"
the cable has a diameter of 0.4 inches and
wave impedance 50  Ohm.
Connecting workstations
produced through a special
device called
transceiver.           Transceiver
connects to computer
multi-core transceiver
cable.  Transceivers between each other
connected by sections of thick
coaxial cable with
connecting connectors on
ends.   The transceiver has one
input for transceiver cable and
one output for "yellow" cable.
Unfortunately, there is
many restrictions that
necessaryadhere to
network installation. So, for example,
the length of one segment should not
exceed 500 meters.  If
the network length still exceeds
500M, then a special
repeater device,
installed on coaxial
cable using special
DIX-connectors.  Repeater functions
consist of physical
separation of network segments and
ensuring recovery
packets transmitted from one
segment to another.  Undoubtedly
repeaters are very convenient and useful,
but unfortunately they are slowing down
network operation. Repeaters can be
made as separate
structures, and in the form of boards,
inserted into expansion slots
computer.    Second option
somewhat worse, because    for
continuous network operation
must be kept constantly
one of the workers is included
station where it is located
repeater  An external repeater can
combine segments completed
on thin and thick coaxial
cables    When using
"yellow" cable quantity
segments should not exceed
five. Thus, the maximum
possible network length - 2,SKm. K
one segment can be connected
no more than 100 computers, and
if there are repeaters in the network, they
are also considered computers.
The transceiver cable cannot
be longer50M, and the distance
between network workers
stations should not be less than
2.5M.  As can be seen from the above
characteristics, networks built
on a thick coaxial cable,
mainly designed for large
institutions, for small and medium-sized
enterprises have such opportunities
networks are clearly redundant. There is
much cheaper and simpler
construction option Ethernet -
networks on thin coaxial
cable    Essentially thin
coaxial cable is different
from thick only in diameter
(thin cable diameter 0.2
inches). However, the network built
on a thin cable, has
significantly different
characteristics.              When
using a thin cable
there is no need for
using transceivers, and
therefore, transceivers
cables.   Network connection
adapters tocoaxial cable
happens with the help of this
called T-connectors.
T-the connector has the shape of a letter T,
one side of it is connected to
network adapter, and the other two
serve as entrance and exit for
coaxial cable. At the ends
segments must be
special plugs called
terminators.      One of
there must be terminators
grounded, for this purpose on it
additional
wire  It should be noted that
characteristics of the network built
on a thin coaxial cable,
somewhat worse than the networks,
built on thick.  Yes,
the length of one segment should not
exceed 185 meters.
Maximum quantity
segments are the same as those
"yellow" cable. Therefore,
the total length of the network can
reach 925 meters. On every
from segments is set to
30  stations.   Moreover, network
stations must be spaced
from each other no less than
0.5 meters.  Network based
thin coaxial cable
is an excellent option for
medium enterprises, but its
the possibilities are clearly excessive for
office applications.  Ideal
network option for small
offices can have a network on twisted
couple, or simply telephone
wire.       Judge for yourself
maximum cable length
segments can reach 100
meters, and the maximum
number of connected stations
- 8, 12 or 16, depending on
the equipment used. Yes and
transfer speed is not at all
less than networks with
coaxial cables, order
1OMb.   On a twisted pair network
a special one is used
device - "hub"to which
all stations are connected, namely
the maximum depends on "hub" and
number of computers on the network.
"Hub"scan be combined between
themselves, obtaining complex cascading
structures. Exceptbesides, usually on
"hub"ah put BNC- and DIX-
connectors, which makes it possible
connect networks together
built on the basis of coaxial
cables and twisted pair.   K
unfortunately, not on all networks
The boards provide an output for
twisted pair, so networks,
built according to the described
structure, still not often
are used.                   
                                
         Network cards.         
                                
Probably, we can say that
the network card is
the main component of any
network, because it depends on it
sending and receiving messages. How
and other internal computer
devices, network cards can
be made on the basis of different
architectures: ISA, VESA, EISA, PCI
(respectively 16-and 32-bit).
If the network is intended for
normal work, not for
one-time rewriting of files,
then the best solution would be
using 32-bit
adapters.  To speed up work
to network cards often
install buffer memory,
the usual size is 1bKb and
more.   When installing network
cards must be specified
interrupt, port base address
input/output and channel number DMA.
This is done using
special jumpers,
located on the map.
Modern network cards
allow customization of their
parameters not with jumpers, but with
software assistance,
supplied with the card.
It has almost become a tradition
what are the manufactured network adapters?
compatible with NE-2000 (NoVell
Ethernet), because  this standard
supported by all network
operating systems without
additional drivers.
Some network manufacturers
cards expanded network capabilities
when using thincoaxial cable, bringing
segment size up to 3000 meters.
However, in order not to disturb
generally accepted standards such
additional cards are placed
jumper switch 185M/
300M.                           
   What should users do?
portable personal
computers of class Notebook? For
they are specially designed
external network cards with
interface PCIMCIA. Outwardly they
look like thin (approximately
Zmm)plates, slightly larger in size
less than a pack of cigarettes, and
functionality
are in no way inferior to similar ones
external devices.    Because of
small thickness PCIMCIA-cards
outputs for connecting cables
are not installed on them.
Outputs are output to
additional adapter,
connected directly to
network card.  As is known,
first models of portable
did not have computersPCIMCIA-
connectors for theirconnections to
networks are used so-called
Pocket-adapters. Pocket-adapters
connected to parallel
port - so talk about
good speed
characteristics of the devices of this
there is no view.             
                                
Network software.
                                
there are two types of network
software: for
networks with a central
control and peer
networks.    Networks with a central
management are built according to
following principle: stands out
central computer, server,
data volume manager
networks.  They put hard ones on the server
large volume disks,
called file servers,
accessible to all other network
computers. Thread management
data is provided as
usually multitasking network
operating system. The rest
network computers are called
workstations, they have
access to allserver resources
and can exchange information
with each other only through
server.  Servers can be like
highlighted.  If users
have the opportunity to work for
server, like on a workstation,
then it is called unallocated.
As a rule, when installing a network
try to leave the server
highlighted, because this approach in
Overall increases network reliability.
There are a lot of different
operating systems,
focused on various
platforms, however most often
meet Microsoft Lan
Manager and NetWare. Peer-to-peer
networks are built a little differently
principle.  Such systems are based
server is not contained.   All
networked computers have equal
priority and have access to
each other's disks.
Peer performance
networks are slightly lower than networks
with central control,
however, this unpleasant fact with
more compensated
achievable amenities in
collaboration between users.
Most popular for
uses peer-to-peer networks
company software
Microsoft - Windows for
Workgroups, and NoVell - NoVell
NetWare. At the same time, it is important
the simplicity with which it is produced
maintenance of peer-to-peer networks.
Judge for yourself - system Windows
for Workgroupsin your own way
the interface is no different from everyone else
well-known shell Windows 3.11.
And the only thing you have to do is
do it just once
configure the system.
After which you will be taken to
familiar shell environment
Windows, with one exception -
now everyone will be available
network printers and hard drives
disks.                          
   Finally, I would like to note
what is the network installation process like?
usually quite labor-intensive - and
if you do not have the proper experience,
then it’s better not to try
perform the installation yourself
cables and software installation
provision.         Exception
perhaps they are peer-to-peer
networks consisting of only
several computers - in this
no need to be big
specialist to install
fully operationalnet. 
          Akimov Sergey         
       (based on materials VKM)      
 SYSTEM.            
                                
               There is nothing better
 what is good to know
 what are you doing.  
                   Peter Norton.
                                
modern computer
is a combination
two important components:
equipment consisting of a whole
a number of devices, and software
collateral representing
is a set of programs for
computer management and
processing of incoming
computer information.           
   Software for
the computer plays something like this
same role as engine for
car, withoutwhom he
just can't move. Between
these components exist
changing over time
cost ratio
"material" (hardware) and
"intelligent" (programs)
product, and not always in
favor of the first. As a rule, this
depends on the degree of difficulty
information processing processes
on the computer.  You can cite
even this comparison: equipment
computers are just
wrapping paper in which
the product itself is wrapped -
software
computer.                     
   Therefore, having received in my hands
computer or just access to
no, very soon, you want this
or not you will also have to
fill it with content,
"interior", which for
computers are used
for information processing
modern applied
programs: text editors,
databases, spreadsheets
etc.                          
   And, of course, no less
your skill will be valuable
take advantage of it all
"wealth".  Carrying out anotheranalogy, we can say that
having an excellent sewing machine and
wonderful material, you also need
be able to sewso that in the end
the result was good.    
   That's why we open
a new section called
"System".     Our name
categories similar to the name
section in the magazine "SPECTROFON",
I’ll say right away that our "System"is not
similar to spectrophon and
it will talk entirely about
friend, about how it works
computer and how to work with
system programs on
computer ZX-SPECTRUM.   This one
section of our magazine will be
useful read for beginners
users and get more
systematic information about
device of computers, although
other users can
find something interesting for yourself
and new.                        
   Special significance
personal computer connected
with its relatively low
cost, which allows
use it in various
large and small institutions or
individuals, as well as
significantopportunities for
processing information that
were available in the recent past
only for largecomputers. However
for personal users
computers such is their status
leads to the need at least
at a minimum level
understand on your own
basic operating principles
computer and its software
provision.   After all, by itself
personal to its name
computer is designed for
individual use.    
   Of course modern
software products created
for personal computer,
trying to provide the maximum
"friendliness"devices
computer and its software
provision, and over time
time this trend
knowledge is increasing, however
basic operating principles
computer will allow more complete
use its capabilities and
avoid many difficulties when
its operation.