This article is from the Amiga FAQ, by Ignaz Kellerer with numerous contributions by others.
PAL and NTSC are two different video standards, the former being European, and the latter being American. PAL has a slightly taller screen (256 lines non-interlaced, non-overscanned) as opposed to NTSC (200 lines), so if you see the bottom portion of a program's screen getting cut off on your American machine, chances are the program was written for PAL, and is running on your shorter NTSC screen. PAL and NTSC differences are somewhat less important to European users; since their machines default to PAL, running an NTSC program is no more than a minor annoyance having the screen only appear in the top portion of the display.
Therefore, for us NTSC folks, switching into PAL mode becomes important to avoid loss of some picture on Euro Demos, etc.
First, the most common misconception about switching between PAL and NTSC is that you need a Multiscan or special monitor for such a purpose. Not so! Just about any monitor can handle the minor signal difference between PAL and NTSC (50Hz vertical refresh versus 60Hz). The 108x, 19xx, and 20xx series, and even most TVs, can display both PAL and NTSC. Sometimes it is necessary to perform minor tweaking of vertical hold and/or v. size on your monitor to achieve full display, though this is trivial.
What IS needed to switch between PAL and NTSC in software, is a "Fatter" (1MB) Agnus or better. If your system has more than 512K of CHIP RAM (use the avail command to find out) you have this chip. If you do not, ou can still construct a hardware switch (see below).
The following directions assume you're an NTSC user who wants to switch into PAL mode, but the procedure for going from PAL to NTSC is much the same.
The most common use of switching into PAL is for self-booting games, demos, etc. The best way to accomplish this on pre-3.0 systems is to use Chris Hames' Degrader program (most recent version: 1.30). Once you have procured this program, the switch is as simple as selecting "50Hz", and "50Hz System", then installing the program's ROMTag (little program that runs at boot-time) by pressing the "Survive Reset(s)" button.
AmigaDOS 3.0 added a PAL/NTSC switch feature to its Boot Menu, and all you need to do in order to access this is hold down both mouse buttons as the computer boots. Select Display Options, Display Mode/PAL, and then Boot. If the program still fails to go into PAL mode (Zool is one I've found), you may wish to get Degrader anyway and try that.
Software PAL/NTSC switching is easy and painless. Some people have gone even further by installing hardware PAL/NTSC switches. This results in a system which even the most nasty hardware-banging programs can't bring to its original configuration (if it has been switched). The procedure is simple - most Amigas have jumpers already - but beyond the scope of this document.
Therefore, if your screen is too short or cut off, seek the different screen mode. You'll "see new horizons", literally!
(Joseph Luk, email@example.com)
---------- Footnotes ----------
(1) PAL/NTSC switching with a MultiSync monitor is possible on 2.0+ and easily accomplished by moving the PAL monitor type to (or NTSC, as applicable, I have them both in) the Devs/Monitors drawer (from the Storage/Monitors drawer), reboot, then go into the Prefs drawer and select the ScreenMode program. You will see at least two PAL modes available (PAL and PAL Interlaced). Simply select one of the (usually non-interlaced for demos) and select "Use". All windows on the Workbench will close, the video mode will change, and then the windows will reopen - that simple!
Allen J. Newton, firstname.lastname@example.org