unsigned int 和unsigned char的区别是什么呢？

void Delay(unsigned int xms)      //unsigned int  和unsigned char 相比为什么int时间就变慢了？
{
    unsigned char i, j;
    while(xms--)
    {
        i = 2;
        j = 239;
        do
        {
            while (--j);
        } while (--i);
        
    }
}

}

unsigned char 0..255
unsigned int 0..4294967295
unsigned short int 0..65535