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Annotation of coherent/a/usr/man/COHERENT/ram, revision 1.1.1.1

1.1       root        1: 
                      2: 
                      3: ram                       Device Driver                       ram
                      4: 
                      5: 
                      6: 
                      7: 
                      8: RAM device driver
                      9: 
                     10: 
                     11: The COHERENT  ram devices allow the user to  allocate and use the
                     12: random access  memory (RAM) of  the computer system  directly.  A
                     13: typical use  is for a RAM  disk, which is a  COHERENT file system
                     14: kept in memory rather than on a diskette or hard disk.
                     15: 
                     16: The COHERENT RAM device driver has major number 8.  It can be ac-
                     17: cessed either as a block-special device or as a character-special
                     18: device.   The high-order  bit  of the  minor number  gives a  RAM
                     19: device number (0 or 1), allowing the use of up to two RAM devices
                     20: simultaneously.  The low-order seven bits specify the device size
                     21: in 64  KB (128 block) increments.   The first open call  on a RAM
                     22: device  with nonzero  size (1  to 127)  allocates memory  for the
                     23: device; the  open call fails  if sufficient memory  is not avail-
                     24: able.  Accessing a RAM device with a minor number specifying size
                     25: 0  frees the  allocated memory, provided  all earlier  open calls
                     26: have been closed.
                     27: 
                     28: Initially, COHERENT includes  two RAM block devices, 512KB device
                     29: /dev/ram0 (8,  8) and 192KB  device /dev/ram1 (8,  131).  It also
                     30: includes /dev/ram0close (8,  0) and /dev/ram1close (8, 128).  The
                     31: system administrator  should change the RAM  devices to sizes ap-
                     32: propriate for available system memory.
                     33: 
                     34: ***** Note *****
                     35: 
                     36: The  COHERENT  installation program  /etc/build  uses RAM  device
                     37: /dev/ram1 as a  RAM disk during installation.  Programs compress,
                     38: uncompress, zcat and  fsck sometimes use /dev/ram1 as a temporary
                     39: storage device.  Users should avoid using /dev/ram1 as a RAM disk
                     40: because of these programs.
                     41: 
                     42: ***** Examples *****
                     43: 
                     44: The following example  formats and mounts a 512-kilobyte RAM disk
                     45: on directory /fast.
                     46: 
                     47: 
                     48:         mkdir /fast
                     49:         /etc/mkfs /dev/ram0 1024
                     50:         /etc/mount /dev/ram0 /fast
                     51: 
                     52: 
                     53: When the  RAM disk is no longer needed,  its allocated memory can
                     54: be freed as follows:
                     55: 
                     56: 
                     57:         /etc/umount /dev/ram0
                     58:         cat /dev/null >/dev/ram0close
                     59: 
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                     63: 
                     64: COHERENT Lexicon                                           Page 1
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                     68: 
                     69: ram                       Device Driver                       ram
                     70: 
                     71: 
                     72: 
                     73: The  next example  replaces  the default  /dev/ram0  with a  one-
                     74: megabyte device containing a COHERENT file system.  The new minor
                     75: number 16  specifies RAM device 0 and size  16 times 64 kilobytes
                     76: (i.e., one  megabyte).  The new RAM  device contains 2,048 blocks
                     77: of 512 bytes each.
                     78: 
                     79: 
                     80:         rm /dev/ram0
                     81:         /etc/mknod /dev/ram0 b 8 16
                     82:         /etc/mkfs /dev/ram0 2048
                     83: 
                     84: 
                     85: ***** Files *****
                     86: 
                     87: /dev/ram*
                     88: 
                     89: ***** See Also *****
                     90: 
                     91: compress, device drivers,  fsck, mkfs, mount, umount, uncompress,
                     92: zcat
                     93: 
                     94: ***** Notes *****
                     95: 
                     96: Moving frequently  used commands or  files to a RAM  disk can im-
                     97: prove system performance substantially.  However, the contents of
                     98: a  RAM device  are lost  if the system  loses power,  reboots, or
                     99: crashes, so changes to files kept  on a RAM disk should be stored
                    100: frequently to the hard disk or to diskette.
                    101: 
                    102: If a RAM device uses most but not all of available system memory,
                    103: its open  call will succeed but subsequent  commands may fail be-
                    104: cause insufficient memory remains for the system.
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                    130: COHERENT Lexicon                                           Page 2
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