Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP Path: utzoo!mnetor!seismo!lll-crg!ames!ucbcad!ucbvax!mdavis@seismo.css.gov@pro-sol.UCSD.EDU From: mdavis@seismo.css.gov@pro-sol.UCSD.EDU (Morgan Davis) Newsgroups: comp.sys.apple Subject: Re: screen memory question (oops!!) Message-ID: <8612101434.AA05630@crash.UUCP> Date: Wed, 10-Dec-86 02:35:09 EST Article-I.D.: crash.8612101434.AA05630 Posted: Wed Dec 10 02:35:09 1986 Date-Received: Mon, 15-Dec-86 06:11:02 EST Sender: daemon@ucbvax.BERKELEY.EDU Organization: The ARPA Internet Lines: 24 WHOA! STOP! Someone suggested using BSAVE's and BLOAD's to save and restore video memory. That works fine for graphics images, but you CANNOT do such a thing with text video RAM. (well, you can, but it might really fry your system). In an earlier message, I talked about "screen holes" in the video display memory between $400 - $7ff in the Apple's main 40-column video bank. Those screen holes are reserved for peripheral card usage, and the disk operating system will also make use of some of them. By disturbing this RAM in any way, unpredictable results might occur. The only way you can safely save and load a screen image using a disk for storage is to move only the display characters from video RAM into a safe buffer, and then write it to disk (or ramdisk). To read the image from disk, you must load the file into a a safe buffer, and use a memory move to copy those bytes back into the display memory (leaving the screen holes unscathed). A word to the wise. --Morgan Davis UUCP: [ akgua, hplabs!hp-sdd, sdcsvax, nosc ] !crash!pnet01!pro-sol!mdavis ARPA: crash!pnet01!pro-sol!mdavis@nosc