15 ms·

The thing that really surprised me is how rare actual IBM MCGA cards were, yet the MCGA-compatible VGA mode was so widely used.

by Dwedit 5mo ago

torgoguys 5mo ago
Because it was the only "standard" 256-color mode back in the day, supported by both mcga and vga. MCGA cards had just enough ram to support this mode (64kb) while vga cards were a strict superset and had a full 256k of ram.
- Dwedit 5mo ago
  The memory is organized differently, where VGA has to use 4 memory chips and spread a byte of memory among them, while MCGA just keeps it simple and uses one byte of memory per pixel.
  - rasz 5mo ago
    Technically in MCGA mode VGA doesnt spread individual pixel bits among banks, pixels are kept "whole" as bytes in banks/planes. 13h is the only mode that doesnt benefit from all of that complicated EGA inherited machinery, yet it still became the most successful and practically synonymous with VGA :) Btw OG 1987 $595 IBM PERSONAL SYSTEM/2 DISPLAY ADAPTER https://www.minuszerodegrees.net/video/IBM%20Announcement%20Letter%20187-054.txt https://www.minuszerodegrees.net/video/IBM%20Announcement%20... VGA card used eight 64Kx4 DRAMs https://upload.wikimedia.org/wikipedia/commons/3/3f/IBM_VGA_graphics_card.jpg https://upload.wikimedia.org/wikipedia/commons/3/3f/IBM_VGA_... to build its 4 banks. Ram Address Bus is wired in parallel (can see pin10 A7 common for 2 rows of ram chips, also pin1 OE).
fredoralive 5mo ago
MCGA was basically a cut down VGA on the motherboard of the low end 8086 / ISA PS/2s, and both chipsets were introduced at the same time. Next-to-no-one would want a not-quite-VGA that lacks high res colour or EGA modes, so nearly nobody bothered cloning it, only the higher end option. The only known clone is in a couple of Epson models, and like the PS/2s it’s a motherboard integrated chip, not an expansion board.

15 ms·

The thing that really surprised me is how rare actual IBM MCGA cards were, yet the MCGA-compatible VGA mode was so widely used.

by Dwedit 5mo ago

The thing that really surprised me is how rare actual IBM MCGA cards were, yet the MCGA-compatible VGA mode was so widely used.

torgoguys 5mo ago
Because it was the only "standard" 256-color mode back in the day, supported by both mcga and vga. MCGA cards had just enough ram to support this mode (64kb) while vga cards were a strict superset and had a full 256k of ram.
- Dwedit 5mo ago
  The memory is organized differently, where VGA has to use 4 memory chips and spread a byte of memory among them, while MCGA just keeps it simple and uses one byte of memory per pixel.
  - rasz 5mo ago
    Technically in MCGA mode VGA doesnt spread individual pixel bits among banks, pixels are kept "whole" as bytes in banks/planes. 13h is the only mode that doesnt benefit from all of that complicated EGA inherited machinery, yet it still became the most successful and practically synonymous with VGA :) Btw OG 1987 $595 IBM PERSONAL SYSTEM/2 DISPLAY ADAPTER https://www.minuszerodegrees.net/video/IBM%20Announcement%20Letter%20187-054.txt https://www.minuszerodegrees.net/video/IBM%20Announcement%20... VGA card used eight 64Kx4 DRAMs https://upload.wikimedia.org/wikipedia/commons/3/3f/IBM_VGA_graphics_card.jpg https://upload.wikimedia.org/wikipedia/commons/3/3f/IBM_VGA_... to build its 4 banks. Ram Address Bus is wired in parallel (can see pin10 A7 common for 2 rows of ram chips, also pin1 OE).
fredoralive 5mo ago
MCGA was basically a cut down VGA on the motherboard of the low end 8086 / ISA PS/2s, and both chipsets were introduced at the same time. Next-to-no-one would want a not-quite-VGA that lacks high res colour or EGA modes, so nearly nobody bothered cloning it, only the higher end option. The only known clone is in a couple of Epson models, and like the PS/2s it’s a motherboard integrated chip, not an expansion board.