Visit Our UNIX and Linux User Community

Linux and UNIX Man Pages

Test Your Knowledge in Computers #1010
Difficulty: Easy
The number 200 in base 8 equals 128 in base 10.
True or False?
Linux & Unix Commands - Search Man Pages

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)

Check Out this Related Man Page

SI(4)							     Kernel Interfaces Manual							     SI(4)

NAME
si - SI 9500/CDC 9766 moving head disk SYNOPSIS
/sys/conf/SYSTEM: NSI si_drives # SI 9500 driver for CDC 9766 disks /etc/dtab: #Name Unit# Addr Vector Br Handler(s) # Comments si ? 176700 170 5 siintr # si9500 major device number(s): raw: 18 block: 9 minor device encoding: bits 0007 specify partition of SI drive bits 0070 specify SI drive DESCRIPTION
Files with minor device numbers 0 through 7 refer to various portions of drive 0; minor devices 8 through 15 refer to drive 1, etc. The standard device names begin with ``si'' followed by the drive number and then a letter a-h for partitions 0-7 respectively. 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 origin and size (in sectors) of the pseudo-disks on each drive are as follows: SI 9500/CDC9766 partitions: disk start length cyls comments xp?a 0 9120 0 - 14 / xp?b 9120 9120 15 - 29 swap xp?c 18240 234080 30 - 414 xp?d 252320 247906 415 - 822* xp?e 18240 164160 30 - 299 /usr xp?f 182400 152000 300 - 549 xp?g 334400 165826 550 - 822* xp?h 0 500384 0 - 822 whole pack Those partitions marked with an asterisk (``*'') actually stop short of the indicated ending cylinder to protect any bad block forwarding information on the packs. The indicated lengths are correct. Partition ``h'' must be used to access the bad block forwarding area. N.B.: the si driver does not support bad block forwarding; the space is reserved in the event bad block forwarding is ever added to the driver. FILES
/dev/si[0-7][a-h] block files /dev/rsi[0-7][a-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), rk(4), rl(4), rp(4), rx(4), xp(4), dtab(5), autoconfig(8) DIAGNOSTICS
si%d%c: hard error sn%d cnr=%b err=%b. An unrecoverable error occurred during transfer of the specified sector of the specified disk par- tition. The contents of the two error registers are also printed in octal and symbolically with bits decoded. The error was either unre- coverable, or a large number of retry attempts (including offset positioning and drive recalibration) could not recover the error. si%d%c: hard error sn%d ssr=%b err=%b. An unrecoverable error occurred during transfer of the specified sector of the specified disk par- tition. The contents of the two error registers are also printed in octal and symbolically with bits decoded. The error was either unre- coverable, or a large number of retry attempts (including offset positioning and drive recalibration) could not recover the error. 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. The partition tables for the file systems should be read off of each pack, as they are never quite what any single installation would pre- fer, and this would make packs more portable. 3rd Berkeley Distribution August 20, 1987 SI(4)

Featured Tech Videos