GLaBIOS

(General Libraries and Basic Input Output System)

A modern, scratch-built, open-source alternative BIOS for vintage PC, XT, 8088 Clone or Turbo PCs.

Copyright (c) 2022, 640KB and contributors.

Video Performance

The BIOS INT 10h CGA and MDA routines were written to be as quick as possible. This can have a major visible impact on almost all UI functions, such as directory listing, text scrolling/movement in both DOS and many programs.

Here are the results of a few simple video benchmarks that were written to measure the overall speed/performance during development, timed using the BDA counter for a resolution of ~55ms. These were then run on some other BIOS ROM binaries found here as baselines for comparison.

CGA Text Drawing / Scrolling

This tests the BIOS TTY (AH = 0Eh) and text scrolling (AH = 6h and 7h). It tests scrolling a two page document using the BIOS “Teletype output” (AH = 0Eh) first starting from a blank screen to simulate writing 1 page without scrolling and then 1 page with scrolling. The test is then repeated by starting at the bottom of a page and writing 2 full pages scolling both.

All BIOS’es tested (appeared to) have some type of CGA snow removal.

MDA Text Drawing / Scrolling

This repeats the test as above, except that in MDA mode memory can be written directly without the necessity of CGA snow removal.

CGA Graphics Drawing

This is a simple benchmark program drawing simple checkerboard patterns using only the BIOS INT 10h AH = 0Bh write graphics pixel routines in both 320x200 and 640x200 resolutions.