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



NAME
     ram - ram disk driver

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

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

DESCRIPTION
     The _r_a_m pseudo-device provides a very fast extended memory
     store.  It's use is intended for file systems like /_t_m_p 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 _r_a_m__s_i_z_e (though a patched system would have to be
     rebooted before any change took effect; see _a_d_b(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 _r_a_m 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 /_t_m_p on it.
     Note that if this arrangement is recorded in /_e_t_c/_f_s_t_a_b then
     /_e_t_c/_r_c will have to be modified slightly to do a _m_k_f_s(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
     _r_a_m__s_i_z_e was set to zero.

BUGS
     The _r_a_m driver is only available under 2.11BSD.







































Printed 11/26/99	Januray 27, 1996			2