Info-Grade

 
#define N 100 /* number of slots in the buffer */
typedef int semaphore; /* semaphores are a special kind of int */
semaphore mutex = 1; /* controls access to critical region */
semaphore empty = N; /* counts empty buffer slots */
semaphore null = 0; /* counts full buffer slots */
void producer(void){
    int item; 
    message m;      // message buffer. 
    while(TRUE){
        item = produce_item(); // generate something to put in buffer 
        receive(consumer, &m); // Receive an empty message, if any 
        build_message(&m, item); // construct a message to send 
        send(consumer, &m);  // send item to consumer 
    }
} 
void consumer(void){
    int item, i; 
    message m; 
    for(i=0; i<N; i++)
        send(producer, &m);  // send N empty messages 
    while(TRUE){
        receive(produce, &m);  // get message containing item   
        item = extract_item(&m); // extract item from message
        send(producer, &m); //send back empty replay 
        consumer_item(term); //do something with the item
    }
}

• Vacuum Tubes provide very unreliable and a programmer, wishing to run his program, could quite easily spend all his/her time searching for an replacing tubes that had blown. 
• Development of Transistor : Now, instead of programmers booking time on the machine, the computers were under submitted on punched cards that were placed onto a magnetic tape. This tape was given to the operators who ran the job through the computer and delivered the output to the expectant programmer. 
• Concept of batch-processing (jobs): Instead of submitting one job at a time, many jobs were placed onto a single tape and these were processed one after another by the computer. The ability to do this can be seen as the first real operating system. 

• IC (Integrated circuit) as a replacement for transistors : The third generation saw the start of multi programming. This is the computer could give the illusion of running more than one task at a time. 
• When one job had to wait for I/O request, another program could use the CPU. The concept of multi-programming led to a need for a more complex operating system. 
• Another feature of third generation machine was that they implemented spooling. This allowed reading of punch cards onto disc as soon as they were brought into the computer room. This eliminated the need to store the jobs stored to disc, thus allowing programs that produced output to tun at the speed of the disc, and not the printer. 
• Up until these point programmers were used to giving their job to an operator and watching it run. 
• This concept led to the concept of time sharing. This allowed programmers to access the computer from a terminal and work in an interactive manner. 
• Obviously, with the advent of multi programming, spooling and time sharing, operating system had to become a lot more complex in order to deal with all these issues.