Path: utzoo!censor!geac!torsqnt!lethe!yunexus!ists!helios.physics.utoronto.ca!news-server.csri.toronto.edu!bonnie.concordia.ca!thunder.mcrcim.mcgill.edu!snorkelwacker.mit.edu!usc!zaphod.mps.ohio-state.edu!rpi!raster From: raster@itsgw.rpi.edu (Jerry D Bain) Newsgroups: comp.sys.ibm.pc.hardware Subject: Re: Question about 1 meg VGA cards Message-ID: Date: 11 Jan 91 20:01:09 GMT References: <4839@umbc3.UMBC.EDU> Lines: 22 Nntp-Posting-Host: jec404.its.rpi.edu chuck@umbc5.umbc.edu (Chuck Rickard) writes: >Just thinking about the memory involved in displaying a 1024x768 256 color >picture... >1024 pixels x 256 colors = 1 K bytes per row >1 K bytes x 768 rows = 768 K bytes >So, the most memory required to display such a picture is 768K, right? >What is done with the other 232K left over in the 1 meg of video memory? Yes, all video cards that require 1meg of memory for 1024x768x256 are wasting memory. Usually the memory gets fragmented due to the strange paging techniques the various chip sets use to get access to the meg of memory through the 64k VGA "window"... I once asked an engineer at an *unnamed* video board manufacturer what the deal was... He responded that the inefficient use of memory was a result of an attempt at getting the base cost down on the control circuitry. With the paging that is used (on most boards), the memory gets fragmented as a result of the attempt to simplify the calculation of addresses that are on power of 2 boundries.