Millennium Time Capsule/AC2000.BIN/disks/ac10disk/atozbook/v.txt

Text File | 1998-06-10 | 30KB | 696 lines

                             "The Atari A to Z"
                              by Mark S Baines
                      Copyright (c) 1998 Mark S Baines
                             All Rights Reserved


       YOU MUST READ "READ_ME.NOW" BEFORE YOU LOOK AT ANY OF THIS FILE
*****************************************************************************


V


V
Volts or Voltage.


V number
Such as V.22, V.42bis. A CCITT or ITU Recommendation concerning the standards
for modems, interfaces and the signals they carry. Some V numbers of interest
are:

  Table V1: Common V Numbers

  V.3       Definition of International Alphabet No. 5
  V.4       The representation of binary 1 and 0, use of parity bits and
            stop/start elements.
  V.21      300 bps asynchronous modems
  V.22      600 and 1,200 bps synchronous and asynchronous modems
  V.22bis   2,400 bps synchronous and asynchronous modems
  V.23      600/1,200/75 bps asymmetric protocol
  V.24      Interface between modem and computer (equivalent to RS-232C port)
  V.29      9,600 bps half duplex protocol used by Group 3 FAXs, and in some
            modems, but with proprietary additions.
  V.32      9,600 bps full duplex
  V.32bis   14,400 bps full duplex
  V.34      28,800 bps full duplex later upgraded to 33,600 bps
  V.42      Error correction for modems, including the MNP 2, 3 & 4 classes
            with LAP-M being optional.
  V.42bis   Data compression for modems, enhancement to V.42 with LAP-M and
            MNP 5 support.
  V-Fast    An unratified standard for 24,000-28,800 bps adaptive protocol
            used by many modem manufacturers before V.34 was approved.
  VFC       V-Fast Class, as V-Fast.
  V.90      56,600/33,600 bps asymmetric protocol (56,600 bps receive, 33,600
            bps receive/transmit)


Valid
Conformance to a standard or criteria, for instance 'valid input' is data that
has been checked for errors.


Validation
A computer program operation to check operator input to ensure that entered
data conforms to certain standards. A database program will validate input to
ensure that the data fits within a field length, that it is of the correct
type (i.e. numeric or alphabetic where necessary), that dates are legal, that
required fields have data in them etc.


Validity check
To check that a particular bit-pattern character is a valid character in the
code in which it is used.


Value
An individually accessible item having some worth or measure.


Vapourware
A product that, having been promised for release for some time, never appears
for sale.


VAR
Value-Added Retailer or Value-Added Reseller. A company that buys computer
systems and resells them at a profit, often also supplying some additional
service with the goods, such as training, installation or maintenance.


Variable
A unit of storage with specified attributes that is declared for purposes of
holding specific data or parameters that may change during or between
executions of a program. A local variable can only be referenced within the
program block in which it was declared and a global variable is available
throughout a program. In mathematics, a variable is a quantity that can assume
any of a given set of values. Also, that which can change not having a fixed
value or form.


Variable declaration
In programming, a statement that establishes the size, structure and data type
of a variable, such as in C the statement char name[20] which specifies a
memory space called name for 20 characters (bytes).


Variable-length record
A record in a database with a length that depends on its contents and not of
fixed-length. They have the advantage of saving on memory and storage space
but are harder to operate on as the end of each record is not predetermined.


VBL
Vertical BLank interrupt. An exception which is triggered as the screen raster
beam returns to the left-hand edge of the top scan line from the bottom right
of the screen, which may be 50, 60 or 70 times a second depending on the
resolution, monitor and country. Because of its strict timing they are used by
periodically executing programs such as TSRs or screen display modifiers and
TOS uses it to erase and display the mouse cursor as it moves across the
screen. A programmer can access a VBL by taking over the exception vector 28
(level 4 interrupt) at address $70 or better still, link into the VBL queue,
the address of which is held at $456 (system variable _vblqueue).


VCS
Video Computer System or Video Console System. A microprocessor computer
system with the primary function of interfacing with a video display, such as
a TV to play games. Atari have two such systems available. The 2600 Video
Computer System offers 192 x 160 pixel resolution, uses plug-in cartridges for
instant load and game play and connects to any domestic TV. The processor is
an 8-bit 6507 (an uprated 6502) and the system is controlled with one or two
joysticks. The cost of the system and the cheap cartridges made it a very
popular buy with over one million sold in the UK alone.

The 7800 Video Game System is more advanced, with 320 x 242 pixel resolution,
256 available colours and characters, 64 software sprites on screen at once, a
6502 'Sally' processor and two sound channels. It is compatible with the 2600
system cartridges and is controlled by two joypad controllers.


VDI
Virtual Device Interface. That part of GEM that provides the device
independent graphical primitive routines for GEM dealing with point plotting,
line drawing, area filling and text drawing among other things with output to
printers, plotters and the screen. There is also an input/output system and it
deals with the mouse and keyboard. GDOS, GIOS and metafiles are the VDI's
responsibility.

The VDI function names have a consistent set of prefixes.

  Table V2: VDI Function Name Prefixes

  Prefix                   Meaning
  v_                       Configuration, graphical output, e.g. v_rc()
  vex_                     Vector handling, e.g. vex_butv()
  vm_                      Metafile specific routines, e.g. vm_coords()
  vq_                      Workstation inquiry routines, e.g. vq_color()
  vqf_, vql_, vqm_, vqt_   Graphical primitive functions, e.g. vqt_extent()
  vqin_                    Inquire input mode, e.g. vqin_mode()
  vqp_                     Inquire palette attributes, e.g. vqp_state()
  vr_, vro_, vrt_          Raster operations, e.g. vro_cpyfm()
  vrq_                     Request mode input, e.g. vrq_locator()
  vs_                      Workstation configuration, e.g. vs_clip()
  vsc_                     Configure mouse form, e.g. vsc_form()
  vsf_                     Set fill area attributes, e.g. vsf_color()
  vsin_                    Set input mode, e.g. vsin_mode()
  vsl_                     Set line attributes, e.g. vsl_ends()
  vsm_                     Set marker types, e.g. vsm_type()
  vsp_                     Set palette attributes, e.g. vsp_save()
  vst_                     Set text attributes, e.g. vst_effects()
  vswr_                    Set writing mode, e.g. vswr_mode()


VDU
Visual Display Unit. A display device with keyboard used to communicate with a
computer. VDUs were originally dumb terminals but most are now intelligent and
interactive. The standard display of 80 or 132 columns and 12 or 24 lines is
still used today. The term is now loosely applied to any display device or CRT
terminal.


Vector
In graphics and mathematics, a directed line segment defined by the
coordinates of its ends or by the coordinates of its origin, its direction and
length. Also, a pointer, a location in memory used to store the address of an
executable routine. TRAP vectors contain the main entry points of the TOS
subroutines.


Vector fonts
See Scalable font.


Vectored interrupt
An interrupt that identifies the cause.


Vector image
A graphic image produced by an object-oriented drawing program where the image
data is stored as a series of vectors and other instructions rather than as a
bitmap. Such images tend to be independent of any output device and can be
scaled without loss of detail. See Drawing program, GEM metafile, Bitmap
image.


VectorPad
An Atari pressure sensitive pad found on the ST Book in place of a mouse. It
is pressed with the fingers in the direction where the mouse cursor is to
move, the greater the pressure the faster the movement. Two extra pads act as
mouse buttons. Similar devices are found on portable games consoles.


Verification
The operation of determining whether a condition that is supposed to exist
does, in fact, exist. With computer data, it is the process of checking manual
operations in an attempt to ensure that they have been performed correctly and
has traditionally meant the checking of transcription errors from one medium
to another, such as from paper to computer bit-patterns.


Verify
To determine whether an operation has been performed correctly. See Write
verify.


Version number
A program generation or edition number indicating its development status with
regard to changes, improvements and bug fixes.


Vertical tabulation
To move paper through a printer in order to move the print head to a lower
position on the page.


Vetting
Synonymous with validation.


VGA
Video Graphics Adaptor. A standard of video display with up to 256 colours and
a typical resolution of 640 x 480 x sixteen colours common on PC compatibles
and the Falcon030. The TT has a similar resolution (TT medium resolution).


VIDEL
The Atari custom chip video controller in the Falcon030 which controls most
video functions including overscan, overlay mode and true-colour graphics. It
is STE SHIFTER compatible. VIDEL sits on a 32-bit data bus.


Video
A term applied to the techniques and equipment involved in presenting data or
other images to CRT screens.


Video buffer
The RAM used to hold the bit-pattern data of the image to be displayed on a
CRT screen. See Logbase and Physbase.


Videotex
A television-based information system, either Teletext or Viewdata.


Viewdata
A system by which textual information is transmitted on demand from a central
computer to a subscriber's special or adapted TV set via a modem and telephone
line. Prestel is the UK's public system. Such systems may provide 'gateways'
to other information providers, such as mail-order catalogues and British
Rail. The display character set is not ASCII-based and provides for a 40
column and 25 line display with eight colours and extremely low resolution
block graphics. This, the slow response time and the very basic control
command set make a Viewdata system a good low technology information provider
for the 'masses' but a poor system for those that need quick, extensive up-to-
date information, searched for on certain criteria and processed for input
into a user program, such as a database.


Virtual
A term used to indicate that the actual physical implementation of something
(a storage system, a peripheral device or communications link) is different
from that perceived by a user or program.


Virtual address
An address in source or object code that has not yet been mapped onto real
storage.


Virtual device
A programming identification of a peripheral device that is not an
identification of any specific device.


Virtual disk
A part of a magnetic disk that is treated by the operating system as a
separate disk, such as a hard disk partition under TOS.


Virtual drive
A direct access drive that does not actually exist but which is implemented
from mass storage, such as a hard disk partition or a RAM disk.


Virtual image
A complete graphic image held in storage of which only a part can be displayed
on the screen at any one time.


Virtual memory
Also, virtual storage. The total range of addresses available for use in a
computer that is organized so that there is no direct relationship between
locations specified in programs and locations actually available in storage
hardware. Such systems will often use hard disk storage as RAM or bring in
pages and/or segments of RAM not in the main address range into main storage
when required. Virtual storage is common on microcomputers that have an
architecture or operating system that limits the amount of RAM they can
address, such as IBM PC compatibles and 8-bit computers. Multi-user,
multiprogramming systems also use virtual storage as the demands on the system
increase.


Virtual reality
A form of imaginary 'space' created in a computer and perceived by a user
through computer I/O devices using stereo sound and vision and tactile
feedback devices. Computer-generated worlds in three dimensions can be
interacted with and moved about in using these techniques, which apart from
the obvious entertainment value, have serious applications in science and
technology, such as 'manipulating' individual atoms in a molecule or
travelling through the inside of a nuclear reactor.


Virtual storage
See Virtual memory.


Virus
A computer virus is a small program that has the primary function of copying
itself, unseen by a user, from one disk to another and hence from one computer
to another. In this manner they 'breed' and 'infect' a computer mimicking the
effect of a biological virus. Most viruses have a secondary function which may
be innocuous, such as showing the programmer's name on screen at boot-up, but
most are more sinister and designed to corrupt data in memory or on disk. Some
will go as far as deleting files, formatting disks or corrupting FAT and
directory tables on disks making them unusable. Under these circumstances, it
has to be assumed that any and all viruses are dangerous and infection by them
should be avoided at all costs. Even self-proclaimed harmless viruses should
not be tolerated as the user can have no idea of the real effect of a virus in
the long term. Until a law can be passed which will outlaw such programs
(criminal damage proceedings can and have been brought on those that knowingly
spread viruses), it has to be assumed that virus programmers, if not criminal,
are undesirable, antisocial and irresponsible.

Most viruses exist in the boot sectors of floppy disks. These programs are
auto-loaded at boot-up and install themselves into memory. They then wait
until another disk access is made and copy themselves to the boot sector of
that disk. The swapping of disks amongst friends, PD libraries, magazine cover
disks and illegal copying and spreading of commercial programs all encourage
the spread of viruses in this manner. Infection is best prevented by checking
each new disk with a virus killer or inoculation program which are available
commercially or in the public domain. Respectable magazines and commercial
companies have been known to pass on viruses so a virus killer is a must for
every computer owner. If it is suspected that a virus exists in a computer
then a cold boot will delete it from memory and a boot-up without a disk or a
known uninfected disk will clear the system so that the use of a virus
inoculator program can be safely used to inspect suspect disks. Write-
protecting a disk with the write-protect tab will prevent a virus copying
itself to a disk.

Users may help protect themselves by carrying out other procedures.

Make backups of all software regardless of any software licence you may have
entered into. Prohibiting the making of backups for your own use and safety is
unenforceable and probably against the law.

Use a backup copy to work from, never an original master if at all possible.
Keep these in a safe place preferably in another room and protect them with
the write-protect tab open.

Backup all data, especially on hard disks, at regular intervals onto other
disks.

Check all new disks, commercial or otherwise with a virus killer or immunizer,
such as George Woodside's PD Virus Killer, the German PD Sagrotan or Richard
Karsmakers' Ultimate Virus Killer. Be careful with commercial games and other
auto-booting disks. Do not immunize these as it will remove the boot-up
program and the disk will probably become useless. Be aware that these
programs cannot detect all viruses, but only the ones they know about. Virus
killers are not foolproof and their exclusive use should not be relied upon.

Use an anti-virus program on your boot-up disk.

Load all auto-booting programs into a computer that has just been switched on
with a cold boot. Any virus that may previously have been in the computer
cannot then copy itself onto your disk.

Report any disk infection to the supplier.

Discourage the spread of illegal copies of programs.

Educate your friends into safe habits. Protect yourself by protecting others.

Anti-virus programs are becoming common and their controlled and intelligent
use should be encouraged. These are programs that behave like viruses but
whose purpose is to warn the user of the presence of an executable boot sector
on the disk in the disk drive. Some are self-copying onto other disks, most
are not. The self-copying ones should be discouraged and not used as they may
be as troublesome to others as a true virus. The copying of programs from one
disk to another should always be under the control of a user and not an
invisible program.

Most viruses are boot sector viruses, but some called 'link viruses' are more
insidious. These copy themselves on to the end of executable files. When that
file is run, so is the link virus at the end of it. On an IBM PC compatible, a
file commonly linked to is COMMAND.COM which is an important MS-DOS file and
always run. On the ST, link viruses are less common (there are only about five
known ones). Most link viruses lie dormant, sometimes called 'logic time
bombs', until a certain event happens, such as a program being run a certain
number of times, the link virus being copied a certain number of times or a
particular system date being reached.


Visible
Evident to a user or program, not transparent.


VLSI
Very Large Scale Integration. An integrated circuit with more than about 1000
gates per chip.


VME bus
Versa Module Europe. A common industry standard device interface for add-on
circuit board cards called Eurocards, supporting a fast data transfer rate and
using a single 96-way connector to provide a 16-bit data bus. Motorola first
developed the Versa bus to enable MC68000-based systems to be constructed by
joining circuit boards together. This was developed to allow standard-sized
Eurocards to be used and became the VME bus. The TT has one single-high VME
board backplane where memory space is partitioned to allow the MC68030 to
access 16-bit or 24-bit address cards. The standard is not fully implemented
as devices act as slaves only. This means that a processor add-on card could
not be used which controls the rest of the TT. Additional memory, graphics
boards and Ethernet network boards can all be attached to this port on the TT.
If RAM is installed there, TOS has to be informed about it with a Maddalt()
call. It will be very slow, it is not cacheable, only sixteen bits wide and
not SCSI-accessible (meaning transfers have to be use SCSI-accessible RAM
which is taken care of in the drivers, but it slows it down). The VME port is
only meant for peripherals.


Voice recognition
An operation involved in recognizing spoken words and converting them to a
computer usable form.


Void
Having no value, a gap or space.


Volatile
Not permanent or easily dispensed with. A term applied to memory (normally
RAM) that requires a continuous electrical input in order to retain stored
data, that data being lost when the current is removed.


Volume
A physical unit of magnetizable-surface storage, such as a disk or digital
cassette.


Volume name
A volume identifier usually written to the volume itself. TOS allows disk and
hard disk partitions to have volume names of up to eleven characters, like a
file name.


Volume/tone control chip
A National LMC1992 Computer Controlled Volume/Tone Control chip in the STE, TT
and Falcon030 used to provide volume and tone control of the stereo DMA sound
production.


von Neumann machine
A computer constructed according to the principles made by John von Neumann in
1946, characterized by the use of stored programs and the separation of code
and data in storage. All computers conform to this principle.


VR
Virtual Reality.


VT
Vertical Tabulate. ASCII code 11 that causes a printer to move the paper
upwards and thus the print head to a lower, preset position.


VT52, VT100
Early industry standard general purpose VT52 and VT100 terminals of the DEC
mainframe computers responded to codes - usually escape sequences - to control
the cursor on the screen and various other miscellaneous screen functions,
such as erase, insert, colour control etc. Terminal technology has since
developed but the screen control codes remain, with the effect that most comms
terminal programs can emulate a VT52 or VT100 type terminal. The Atari BIOS
has a VT52 emulator built into it so it understands these codes without
further translation.


VT52 escape control sequences
These codes are a simple and effective way of controlling the screen in TOS
programs but their use is not generally portable to other computers. Examples
of their use are given in C. Numbers, such as \033 are in octal. The first
#define is for inclusion within a printf() statement, such as:

  printf("Today is %s%s%s", R_VID, date, N_VID);

The second #define can be used on its own as a separate statement:

  CLS;
  RVS_VID;
  printf("PROFILE v1.53 By Linnhe Computing (c) 1994\n");
  NORM_VID;

Some of these control sequences are duplicated in the Atari VDI set of Screen
Escape Functions. Examples in C of some possible macros are given after each
definition.

  Table V3: VT52 Control Codes

  ASCII 7                  BELL
  This rings the monitor bell, useful for attracting attention.
  #define BEL              "\007"
  #define BELL             printf("%s", BEL)

  Esc A                    Cursor Up
  Moves the cursor up one line. If the cursor is already on the top line of
  the screen, this has no effect.
  #define C_UP             "\033A"
  #define CUR_UP           printf("%s", C_UP)

  Esc B                    Cursor Down
  Moves the cursor down one line. If the cursor is already on the last line of
  the screen, this has no effect.
  #define C_DOWN           "\033B"
  #define CUR_DOWN         printf("%s", C_DOWN)

  Esc C                    Cursor Right
  Moves the cursor one position to the right. If this would move the cursor
  off the screen, this has no effect.
  #define C_RT             "\033C"
  #define CUR_RT           printf("%s", C_RT)

  Esc D                    Cursor Left
  Moves the cursor one position to the left. This is non-destructive i.e. it
  does not delete the character over which it now rests. If the cursor is
  already in column 0, this escape sequence has no effect.
  #define C_LT             "\033D"
  #define CUR_LT           printf("%s", C_LT)

  Esc E                    Clear Screen (and Home Cursor)
  This moves the cursor to the top left-hand corner of the screen and clears
  all characters from the screen.
  #define CLEAR            "\033E"
  #define CLS              printf("%s", CLEAR)

  Esc H                    Home Cursor
  Moves the cursor to the top left-hand corner of the screen. The screen is
  not cleared.
  #define CUR_HOME         "\033H"
  #define HOME             printf("%s", CUR_HOME)

  Esc I                    Scroll Up
  Moves the cursor up but, in contrast to Esc A, if the cursor is on the top
  line, a scroll down is performed. The column position remains unchanged.
  #define SCRL_UP          "\033I"
  #define SCROLL_UP        printf("%s", SCRL_UP)

  Esc J                    Erase to End of Screen
  Erases all the data from the cursor (including its position) to the end of
  the screen.
  #define E_EOS            "\033J"
  #define ERA_EOS          printf("%s", E_EOS)

  Esc K                    Clear to End of Line
  Clears the line from the current cursor position to the end of the line.
  #define E_EOL            "\033K"
  #define ERA_EOL          printf("%s", E_EOL)

  Esc L                    Insert Line
  Inserts a new blank line by moving the line the cursor is on and all
  following lines down one line; the lowest line is lost. Then the cursor is
  moved to the start of the new blank line.
  #define INSERT_LINE      "\033L"
  #define INS_LINE         printf("%s", INSERT_LINE)

  Esc M                    Delete Line
  Deletes the contents of the line the cursor is on, places the cursor at the
  start of the line, moves all the following lines up one line, and adds a
  blank line at the bottom.
  #define DELETE_LINE      "\033M"
  #define DEL_LINE         printf("%s", DELETE_LINE)

  Esc Y                    Position Cursor
  The two characters that follow the 'Y' specify the line (x) and column (y)
  to which the cursor is to be moved. Lines and columns number from zero
  inclusive, but an offset of 32 (decimal) is expected.
  #define CUR_POS          "\033Y"
  #define CUR_MOVE(x, y)   printf("%s%c%c", CUR_POS, 32 + x, 32 + y)

  To move the cursor to line 7, column 33 enter the line:
  CUR_MOVE(7, 33);

  Esc b                    Foreground Colour
  Sets the character colour (x). In mono mode there is a choice of 0 = white
  and 1 = black. In colour modes on the ST there is a choice of four or
  sixteen depending on the resolution. Only the four least significant bits of
  the colour character are used. You can use the digit 1 as well as the
  letters A or a in addition to binary one.
  #define COL_FORE         "\033b"
  #define INK(x)           printf("%s%c", COL_FORE, x)

  If the current palette has blue as the fourth colour then a line such as:
  INK(4);
  will print all following output statements in blue.

  Esc c                    Background Colour
  Sets the background colour, the colour of the cell that contains the
  characters. The comments above apply. Do not set the foreground and
  background colours the same!
  #define COL_BACK         "\033c"
  #define PAPER(x)         printf("%s%c", COL_BACK, x)

  Esc d                    Erase from Start of Screen
  Erases from the start of the screen to the cursor position. The cursor
  position is erased also.
  #define E_SOS            "\033d"
  #define ERA_SOS          printf("%s", E_SOS)

  Esc e                    Cursor On
  Shows the cursor. The cursor may still be moved about on the screen.
  #define C_ON             "\033e"
  #define CUR_ON           printf("%s", C_ON)

  Esc f                    Cursor Off
  Hides the cursor. The cursor may still be moved about on the screen. Useful
  for getting rid of the annoying flashing cursor when the program is
  displaying output and not requiring any input from the user.
  #define C_OFF            "\033f"
  #define CUR_OFF          printf("%s", C_OFF)

  Esc j                    Save Cursor Position
  Saves the current cursor position. This function is also used by other
  Escape sequences so the stored values are no longer available to you if you
  have used some other code sequence. If you have, the cursor is homed.
  #define C_SAVE           "\033j"
  #define CUR_SAVE         printf("%s", C_SAVE)

  Esc k                    Restore Cursor Position
  Restores the cursor to a previously saved position. If you use this sequence
  without having previously saved the cursor position, then the cursor is
  homed.
  #define C_RESTORE        "\033k"
  #define CUR_RESTORE      printf("%s", C_RESTORE)

  Esc l                    Erase Line
  Erases the current line and moves the cursor to the leftmost column.
  #define E_LINE           "\033l"
  #define ERA_LINE         printf("%s", E_LINE)

  Esc o                    Erase Start of Line
  Erases from the start of the line to the cursor including the cursor
  position.
  #define E_LINE_TO_C      "\033o"
  #define ERA_LINE_TO_C    printf("%s", E_LINE_TO_C)

  Esc p                    Reverse Video Mode
  Enters the reverse video mode so that foreground and background colours are
  exchanged. Useful for highlighting in mono mode.
  #define R_VID            "\033p"
  #define RVS_VID          printf("%s", R_VID)

  Esc q                    Normal Video Mode
  Exits the reverse video mode.
  #define N_VID            "\033q"
  #define NORM_VID         printf("%s", N_VID)

  Esc v                    Automatic Overflow On
  Attempted output past the last screen column will automatically start a new
  line. The page scrolls up if necessary.
  #define LINEWRAP_ON      "\033v"
  #define WRAP_ON          printf("%s", LINEWRAP_ON)

  Esc w                    Automatic Overflow Off
  Deactivates the Esc v above. Writing beyond the last column on the screen
  does not cause a new line but all characters are printed in that column,
  erasing the last character.
  #define LINEWRAP_OFF     "\033w"
  #define WRAP_OFF         printf("%s", LINEWRAP_OFF)


V
55 entries
EOF