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BSD 2.11 - man page for ram (bsd section 4)

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RAM(4)											   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 controlled by the NRAM definition in
       units of 512-byte blocks.  This is also patchable in the system binary through  the  vari-
       able  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 envi-
       ronment.

       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' interface 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  arrange-
       ment  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

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.

3rd Berkeley Distribution		 Januray 27, 1996				   RAM(4)
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