| MEM(4) | Device Drivers Manual (hppa) | MEM(4) | 
mem, kmem —
mem* at mainbus0
mem driver controls and restricts access to the
  systems memory by the hardware buses and the processor.
It also provides an interface to userland through the special files /dev/mem and /dev/kmem. Physical memory is accessed through /dev/mem, while kernel virtual memory is accessed through /dev/kmem. Access to kernel virtual addresses not currently mapped to memory will fail. On hppa, the physical memory range is always contiguous and starts at address 0; kernel virtual memory begins at address 0 as well.
The writeability of the /dev/mem and /dev/kmem special files are controlled by the system securelevel in addition to the filesystem permissions.
mem driver originates from
  OpenBSD. It was ported to NetBSD
  1.6 by Matthew Fredette.
mem
  or hppa/cpu(4) device
  probe.
| February 17, 2017 | NetBSD 10.0 |