RAMDISK(7) RAMDISK(7)
NAME
ramdisk - general ramdisk driver
DESCRIPTION
A ramdisk is a portion of memeory set aside by the operating
system that is accessed in exactly the same manner as a disk
drive but, because it is memory, it has the advantage that
there is no actual device I/O, and there are no interrupts
to wait for. I/O becomes somply a transfer of data from one
portion of memory to another.
The UniSoft SYSTEM V ramdisk driver view each ramdisk device
as a collection of eight slices (partitions). Each slice
has a physical address in memory of the first byte and a
size in bytes. Each slice is accessed through the minor
device number. The minor device number is taken as an index
into the ``struct size'' array ramd_sizes[] contained in the
include file /usr/include/sys/io/ramdio.h. ramdisk unit
zero spans slices zero through seven, unit one spans slices
eight through fifteen, and so on, depending on the number of
ramdisks defined in dfile (see dfile(4)). The special files
/dev/rdsk/ramd0sX and /dev/dsk/ramd0sX refer to ramdisk
unit zero where X is the slice number and dsk or rdsk refer
to system buffered or unbuffered I/O, respectively.
dfile must be modified before system configuration so that
the memory configuration specifications do not overlap
ramdisk slices.
ramd_sizes[] may be modified before system configuration to
contain slicing information to make the ramdisk more
manageable.
SEE ALSO
config(1M), sysgen(1M), chmod(1), dfile(4).
Page 1 May 1989