2.11BSD#431 - /usr/man/cat4/ram.0

RAM(4)		    UNIX Programmer's Manual		   RAM(4)


NAME
     ram - ram disk driver

SYNOPSIS
     /sys/conf/SYSTEM:
	  NRAM ram_size  # RAM disk size (512-byte blocks)

     major device number(s):
	  block: 3
     minor device encoding:
	  must be zero (0)

DESCRIPTION
     The ram pseudo-device provides a very fast extended memory
     store.  It's use is intended for file systems like /tmp and
     applications which need to access a reasonably large amount
     of data quickly.

     The amount of memory dedicated to the ram device is con-
     trolled by the NRAM definition in units of 512-byte blocks.
     This is also patchable in the system binary through the
     variable ram_size (though a patched system would have to be
     rebooted before any change took effect; see adb(1)).  This
     makes it easy to test the effects of different ram disk
     sizes on system performance.  It's important to note that
     any space given to the ram device is permanently allocated
     at system boot time.  Dedicating too much memory can
     adversely affect system performance by forcing the system to
     swap heavily as in a memory poor environment.

     The block file accesses the ram disk via the system's
     buffering mechanism through a buffer sharing arrangement
     with the buffer cache.  It may be read and written without
     regard to physical disk records.  There is no `raw' inter-
     face since no speed advantage is gained by such an interface
     with the ram disk.

DISK SUPPORT
     The ram driver does not support pseudo-disks (partitions).
     The special files refer to the entire `drive' as a single
     sequentially addressed file.

     A typical use for the ram disk would be to mount /tmp on it.
     Note that if this arrangement is recorded in /etc/fstab then
     /etc/rc will have to be modified slightly to do a mkfs(8) on
     the ram disk before the standard file system checks are
     done.

FILES
     /dev/ram		 block file
     /dev/MAKEDEV	 script to create special files
     /dev/MAKEDEV.local  script to localize special files


Printed 11/26/99	Januray 27, 1996			1


RAM(4)		    UNIX Programmer's Manual		   RAM(4)


SEE ALSO
     hk(4), ra(4), rl(4), rk(4), rp(4), rx(4), si(4), xp(4)
     dtab(5), autoconfig(8)

DIAGNOSTICS
     ram: no space.  There is not enough memory to allocate the
     space needed by the ram disk.  The ram disk is disabled.
     Any attempts to access it will return an error.

     ram: not allocated.  No memory was allocated to the ram disk
     and an attempt was made to open it.  Either not enough
     memory was available at boot time or the kernel variable
     ram_size was set to zero.

BUGS
     The ram driver is only available under 2.11BSD.


Printed 11/26/99	Januray 27, 1996			2