ram(4) [bsd man page]

RAM(4)							     Kernel Interfaces Manual							    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 variable 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 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' 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 arrangement 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)

RK(4)							     Kernel Interfaces Manual							     RK(4)

NAME

       rk - RK-11/RK05 disk

SYNOPSIS

       /sys/conf/SYSTEM:
	    NRK  rk_drives # RK05

       /etc/dtab:
	    #Name Unit# Addr   Vector Br Handler(s)	 # Comments
	    rk	  ?	177400 220    5  rkintr 	 # rk05

       major device number(s):
	    raw: 15
	    block: 6
       minor device encoding:
	    specifies drive: <rk_drive>

DESCRIPTION

       Minor  device  numbers  are  drive numbers on one controller.  The standard device names begin with ``rk'' followed by the drive number and
       then the letter "h".  The character ? stands here for a drive number in the range 0-7.

       The block files access the disk via the system's normal buffering mechanism and may be read and written without	regard	to  physical  disk
       records.   There  is also a `raw' interface which provides for direct transmission between the disk and the user's read or write buffer.  A
       single read or write call results in exactly one I/O operation and therefore raw I/O is considerably more efficient  when  many	words  are
       transmitted.  The names of the raw files conventionally begin with an extra `r.'

       In  raw	I/O  the buffer must begin on a word (even) boundary, and counts should be a multiple of 512 bytes (a disk sector).  Likewise seek
       calls should specify a multiple of 512 bytes.

DISK SUPPORT

       The rk driver does not support pseudo-disks (partitions).  Each file rk?h refers to the entire drive as	a  single  sequentially  addressed
       file.  Each drive has 4872 512-byte blocks.

       It's not clear what one would do with one of these drives if one had one ...

FILES

       /dev/rk[0-7]h	   block files
       /dev/rrk[0-7]h	   raw files
       /dev/MAKEDEV	   script to create special files
       /dev/MAKEDEV.local  script to localize special files

SEE ALSO

       hk(4), ra(4), ram(4), rl(4), rp(4), rx(4), si(4), xp(4), dtab(5), autoconfig(8)

DIAGNOSTICS

       rk%d:  hard  error  sn%d  er=%b ds=%b.  An unrecoverable error occurred during transfer of the specified sector of the specified disk.  The
       contents of the two error registers are also printed in octal and symbolically with bits decoded.  The error was either unrecoverable, or a
       large number of retry attempts could not recover the error.

       rk%d: write locked.  The write protect switch was set on the drive when a write was attempted.  The write operation is not recoverable.

BUGS

       In  raw	I/O  read  and	write(2) truncate file offsets to 512-byte block boundaries, and write scribbles on the tail of incomplete blocks.
       Thus, in programs that are likely to access raw devices, read, write and lseek(2) should always deal in 512-byte multiples.

       DEC-standard error logging should be supported.

       A program to analyze the logged error information (even in its present reduced form) is needed.

3rd Berkeley Distribution					  August 20, 1987							     RK(4)