monitors are able to show only a relatively few tone graduations. Although the Applix provides up to 16 shades, not all will be visible on most monochrome monitors. As the Applix video is programmable, a Memory Resident Driver (see the Technical Reference Manual for details) can alter the scan frequencies, and the number of pixels on the screen. It is thus possible to change the display from 640 by 200 pixels, up to 640 by 350 pixels. This requires an increased horizontal scan frequency, and thus a different style of display. A suitable frequency turns out to be closely equivalent to that required by the (non TV standard) IBM Monochrome or Hercules monitor.
Thus we recommend a ‘dual scan’ monitor for monochrome use. The 640 by 350 display (devised by Conal Walsh, who also did the ZRDOS port) is capable of much better text and graphics displays, and is highly recommended. However, in colour, it requires a much more expensive, much higher quality, Multisync monitor. This option gives you the equivalent of IBM EGA output. Prices of these range from round $400 (some of pretty terrible quality) to over $1000 (some of which are very nice indeed). There is also a single chip modifi- cation required in your Applix, although some monitors will run without this change.
Finally, a $30 modification to your Applix allows you to run Stephen A Uhler’s MGR windowing system, ported from Sun Unix workstations, providing multiple, resizable windows and mouse support, on a 940 by 512 display. This requires a Multisync monitor. Ask Applix or the User Group for advice, before you buy a monitor, if this dis- cussion of the differences between monitors is unclear to you. The I/O ports Data going to and from the 1616’s serial ports is buffered and interrupt driven. Thedefault buffer sizeis 200 bytes for input (per channel) and 200 bytes for output. This simply means that a certain amount of communication can take place even when the computer is busy doing other things.
See the documentation for the inbuilt ‘serial’ command for further description of the serial port software. You don’t actually need to know about this, unless you want to use the serial RS232 ports. Data transmission to the parallel printer is also interrupt driven and buffered. The default buffer size is 64 bytes. As with the keyboard buffer, the size of this buffer can be altered by advanced users by means of the new_cbuf system call. Appendix A User Tutorial Manual Page 105