BSD 2.11 - man page for ram (bsd section 4)
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ram - ram disk driver
NRAM ram_size # RAM disk size (512-byte blocks)
major device number(s):
minor device encoding:
must be zero (0)
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-
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.
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.
/dev/ram block file
/dev/MAKEDEV script to create special files
/dev/MAKEDEV.local script to localize special files
hk(4), ra(4), rl(4), rk(4), rp(4), rx(4), si(4), xp(4) dtab(5), autoconfig(8)
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.
The ram driver is only available under 2.11BSD.
3rd Berkeley Distribution Januray 27, 1996 RAM(4)
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