64bit быть или не быть?

Во первых не изчезают а добавляются, а во вторых

localhost temp # cat ./test.c
#include <stdio.h>
#include <stdint.h>
int main()
{
    printf("short is: %d\n", sizeof(short));
    printf("int is: %d\n", sizeof(int));
    printf("char is: %d\n", sizeof(char));
    printf("long is: %d\n", sizeof(long));
    printf("unsigned long long is: %d\n", sizeof(long));
    printf("u_int64_t: %d\n", sizeof(long));
    printf("uint16_t is: %d\n", sizeof(uint16_t));
    printf("uint32_t is: %d\n", sizeof(uint32_t));
    printf("uint64_t is: %d\n", sizeof(uint64_t));

return 0;
}
localhost temp # ./test
short is: 2
int is: 4
char is: 1
long is: 8
unsigned long long is: 8
u_int64_t: 8
uint16_t is: 2
uint32_t is: 4
uint64_t is: 8
localhost temp # uname -a
Linux localhost 2.6.19-gentoo-r2 #1 SMP PREEMPT Thu Dec 14 19:51:13 MSK 2006 x86_64 AMD Athlon(tm) 64 Processor 3200+ AuthenticAMD GNU/Linux

По Вашему long должен быть длиной 6 байт?