Semaphores r software, blocking, OS assistance solution to 
the mutual exclusion problem .It is
basically a non-negative integer variable that saves the 
number of wakeup signals sent so they are not lost if the 
process is not sleeping 

another interpretation is that the semaphore value 
represents the number of resources available 

Semaphore is a machanism to resolve resources conflicts by
tallying resource seekers what is the state of sought
resources, achieving a mutual exclusive access to resources.
Often semaphore operates as a type of mutual exclusive
counters (such as mutexes) where it holds a number of access
keys to the resources. Process that seeks the resources must
obtain one of those access keys, one of semaphores, before
it proceeds further to utilize the resource. If there is no
more such a key available to the process, it has to wait for
the current resource user to release the key.

A semaphore, a new variable type.
A semaphore could have the value 0,indicating that no 
wakeups were saved, or some positive values if one or more 
wakeups were pending.
a semaphore s is an integer variable that apart from 
initialization, is accesssed only through two standard 
atomic operations, wait and signal. these operations were 
orignially termed p(for wait to test) and v(for signal to 
increment).
The classical defination of wait in psedocode is
wait(s)
{
while(s<=0)
;// no-op
s--;
}
The classical defination of signal in psedocode is
signal(s)
{
s++;
}
Modification to the integer value of smaphore in wait and 
signal operations must be executed individually.
that is, when one process modifies the semaphore value no 
other process can simultaneously modifiy that same 
semaphore value.

semopore is s\w