usr/share/man/cat4/tahoe/mem.0

MEM(4)           BSD Programmer's Manual (Tahoe Architecture)           MEM(4)

N\bNA\bAM\bME\bE
     m\bme\bem\bm, k\bkm\bme\bem\bm, v\bvm\bme\bem\bm - main memory

D\bDE\bES\bSC\bCR\bRI\bIP\bPT\bTI\bIO\bON\bN
     The special file /\b/d\bde\bev\bv/\b/m\bme\bem\bm is an interface to the physical memory of the
     computer.  Byte offsets in this file are interpreted as physical memory
     addresses.  Reading and writing this file is equivalent to reading and
     writing memory itself.  Only offsets within the bounds of /\b/d\bde\bev\bv/\b/m\bme\bem\bm are
     allowed.

     Kernel virtual memory is accessed through the interface /\b/d\bde\bev\bv/\b/k\bkm\bme\bem\bm in the
     same manner as /\b/d\bde\bev\bv/\b/m\bme\bem\bm. Only kernel virtual addresses that are currently
     mapped to memory are allowed.

     The file /\b/d\bde\bev\bv/\b/v\bvm\bme\bem\bm allows access to the mapped portion of the VERSAbus
     I/O space.  On the Tahoe the upper megabyte of the physical address space
     is accessible through this file (0xfff00000 through 0xffffffff).  Access-
     es to the upper 64 kilobytes of the I/O space result in VERSAbus trans-
     fers with a 16-bit address (the offset in this region) and a ``non-
     privileged short I/O'' VERSAbus address modifier.  Accesses to the re-
     mainder of the mapped region, result in VERSAbus transfers with a 24-bit
     address and a ``non-privileged standard'' VERSAbus address modifier.
     This region is actually part of the region between 0xfeff0000 and
     0xffff0000 which generates VERSAbus transfers with a 24-bit address.  Ac-
     cesses to the remainder of the one gigabyte I/O space generate transfers
     that utilize a 32-bit address with a ``non-privileged extended'' address
     modifier.  Any 32-bit address generated by a cpu access to this part of
     the I/O space have the upper two bits zero; thus, for example, an access
     to physical address 0xfe000000 causes the address 0x3e000000 to be sup-
     plied in the resultant VERSAbus read/write cycle.

     On the Tahoe, the base address for the per-process data of the current
     process is virtual address 0xbffff000.

F\bFI\bIL\bLE\bES\bS
     /dev/mem
     /dev/kmem
     /dev/vmm

H\bHI\bIS\bST\bTO\bOR\bRY\bY
     The m\bme\bem\bm, k\bkm\bme\bem\bm files appeared in Version 6 AT&T UNIX.  The file v\bvm\bme\bem\bm ap-
     peared in 4.3BSD-Tahoe.

B\bBU\bUG\bGS\bS
     Memory files are accessed one byte at a time, an inappropiate method for
     some device registers.

4.4BSD                           June 5, 1993                                1