HI All, I started to understand output of /proc/oiports and /proc/iomem. I confused to relate these two's output. Below is the kernel source for Mapping of io-port to io-mem. Could anyone please explain below code. /* We encode the physical PIO addresses (0-0xffff) into the (0- * pointer by offsetting them with a constant (0x10000) and * assuming that all the low addresses are always PIO. That means means * we can do some sanity checks on the low bits, and don't * need to just take things for granted. */ #define PIO_OFFSET 0x10000UL #define PIO_MASK 0x0ffffUL #define PIO_RESERVED 0x40000UL void __iomem *ioport_map(unsigned long port, unsigned int nr) { __iomem if (port > PIO_MASK) return NULL; return (void __iomem *) (unsigned long) (port + PIO_OFFSET); __iomem } Thanks, Prabhu