The mem character special device file provides access to physical main memory.
Byte addresses in mem are equivalent to physical memory in RAM. References to I/O space addresses or to nonexistent RAM will return errors. Write accesses to console or PAL memory will also return errors.
Because memory is read and written in aligned quadwords (eight contiguous bytes), writing fewer than all the bytes in an aligned quadword is a read-modify-write operation that is not protected against concurrent writes to the same quadword.
kmem(7) delim off