Same specs as previous system, 8 hours to find all primes to ULONG_MAX.

#include <stdio.h>
#include <malloc.h>
#include <limits.h>
#include <math.h>

struct linked_list
{
    unsigned long number;
    struct linked_list *next;
};

int main(int argc, char **argv)
{
    unsigned long divisor, max_divisor, prime_test;
    unsigned long max_prime_to_store;
    struct linked_list *first=NULL, *current=NULL, *last=NULL;

    first=(struct linked_list *)malloc(sizeof(struct linked_list));
    first->number = 2L;
    first->next = NULL;
    last = first;
    printf("%lun", 2L);

    max_prime_to_store = 1L + sqrt(ULONG_MAX);

    for(prime_test = 3L; prime_test < ULONG_MAX; prime_test+=2L)
    {
        max_divisor=1L+sqrt(prime_test);
        for(current = first; current && current->number <= max_divisor; current = current->next)
        {
            if(prime_test % current->number == 0)
            {
                break;
            }
        }
        if(!current || current->number > max_divisor)
        {
            if(prime_test <= max_prime_to_store)
            {
                last->next = (struct linked_list *)malloc(sizeof(struct linked_list));
                last = last->next;
                last->next = NULL;
                last->number = prime_test;
            }
            printf("%lun", prime_test);
        }
    }
    return 0;
}