Answer by Raffzahn for Why does PC video memory base address change depending...
TL;DR: CompatibilityBefore VGA there was MDA, CGA and EGA and it's all about continued support.IBM reserved the space above A0000h for extensions, with 128 KiB at A000h reserved for Video (*1). In the...
View ArticleAnswer by tofro for Why does PC video memory base address change depending on...
For CGA vs. MDA, the reasoning for using different base adresses is simple and obvious: These two video systems are designed to co-exist for dual-monitor solutions thus each need a unique memory...
View ArticleAnswer by Stephen Kitt for Why does PC video memory base address change...
The history behind the various base addresses is as follows:the area starting at A0000h was set aside for video frame buffers in general (see Who set the 640K limit?)MDA used 16KiB starting at...
View ArticleWhy does PC video memory base address change depending on video mode?
It is rather well-known that, with VGA-compatible PC video adapters, in black-and-white text modes video memory is available at linear address 0xB0000, in colour text mode at address 0xB8000, while in...
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