Q42660: QuickBASIC Updates Screen Faster than CGA Can Update

Article: Q42660
Product(s): See article
Version(s): 4.00 4.00b 4.50
Operating System(s): MS-DOS
Keyword(s): ENDUSER | SR# S890309-13 b_basiccom | mspl13_basic
Last Modified: 22-MAR-1989

This information applies to QuickBASIC Versions 4.00, 4.00b, and 4.50
for MS-DOS and to the Microsoft BASIC Compiler Version 6.00 and 6.00b
for MS-DOS and OS/2.

Below is an example of a basic program that attempts to print data on
a screen. Most video systems are fast enough that all of the
information can be printed to the screen. The Color Graphics Adapter
(CGA) system, however, does not update the screen frequently enough
for all lines to be scrolled up. This results in less than 25 lines of
text being displayed on the screen while the program is printing. The
entire 25 lines will appear on the screen at the end of the loop.
Because this is caused by printing to the screen too fast, if this
presents a problem for some specific application, put a delay loop
inside of the print loop to slow down the print process.

This problem did not occur with earlier versions of QuickBASIC.

Code Example

COLOR 11, 1, 1
d$ = STRING$(80, 65)
FOR d% = 1 TO 1000
  PRINT d$
NEXT

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