1RAM(4) Kernel Interfaces Manual RAM(4)
2
6 ram - ram disk driver
7
9 /sys/conf/SYSTEM:
10 NRAM ram_size # RAM disk size (512-byte blocks)
11 major device number(s):
13 block: 3
14 minor device encoding:
15 must be zero (0)
16
18 The ram pseudo-device provides a very fast extended memory store. It's
19 use is intended for file systems like /tmp and applications which need
20 to access a reasonably large amount of data quickly.
21 The amount of memory dedicated to the ram device is controlled by the
23 NRAM definition in units of 512-byte blocks. This is also patchable in
24 the system binary through the variable ram_size (though a patched sys‐
25 tem would have to be rebooted before any change took effect; see
26 adb(1)). This makes it easy to test the effects of different ram disk
27 sizes on system performance. It's important to note that any space
28 given to the ram device is permanently allocated at system boot time.
29 Dedicating too much memory can adversely affect system performance by
30 forcing the system to swap heavily as in a memory poor environment.
31 The block file accesses the ram disk via the system's buffering mecha‐
33 nism through a buffer sharing arrangement with the buffer cache. It
34 may be read and written without regard to physical disk records. There
35 is no `raw' interface since no speed advantage is gained by such an
36 interface with the ram disk.
37
39 The ram driver does not support pseudo-disks (partitions). The special
40 files refer to the entire `drive' as a single sequentially addressed
41 file.
42 A typical use for the ram disk would be to mount /tmp on it. Note that
44 if this arrangement is recorded in /etc/fstab then /etc/rc will have to
45 be modified slightly to do a mkfs(8) on the ram disk before the stan‐
46 dard file system checks are done.
47
49 /dev/ram block file
50 /dev/MAKEDEV script to create special files
51 /dev/MAKEDEV.local script to localize special files
52
54 hk(4), ra(4), rl(4), rk(4), rp(4), rx(4), si(4), xp(4) dtab(5), auto‐
55 config(8)
56
58 ram: no space. There is not enough memory to allocate the space needed
59 by the ram disk. The ram disk is disabled. Any attempts to access it
60 will return an error.
61 ram: not allocated. No memory was allocated to the ram disk and an
63 attempt was made to open it. Either not enough memory was available at
64 boot time or the kernel variable ram_size was set to zero.
65
67 The ram driver is only available under 2.11BSD.
683rd Berkeley Distribution Januray 27, 1996 RAM(4)