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Mode X in Turbo Pascal, Part 1: Planar Memory and Pages
2026-02-22
Mode 13h is the famous VGA “easy mode”: one byte per pixel, 320x200, 256 colors, linear memory. It is perfect for first experiments and still great for teaching rendering basics. But old DOS games that felt smoother than your own early experiments usually did not stop there. They switched to Mode X style layouts where planar memory, off-screen pages, and explicit register control gave better composition options and cleaner timing.
This first article in the series is about that mental model. Before writing sprite engines, tile systems, or palette tricks, you need to understand what the VGA memory controller is really doing. If the model is wrong, every optimization turns into folklore. ... continue
Mode 13h in Turbo Pascal: Graphics Programming Without Illusions
2026-02-22
Turbo Pascal graphics programming is one of the cleanest ways to learn what a frame actually is. In modern stacks, rendering often passes through layers that hide timing, memory layout, and write costs. In DOS Mode 13h, almost nothing is hidden. You get 320x200, 256 colors, and a linear framebuffer at segment $A000. Every pixel you draw is your responsibility.
Mode 13h became a favorite because it removed complexity that earlier VGA modes imposed. No planar bit operations, no complicated bank switching for this resolution, and no mystery about where bytes go. Pixel (x, y) maps to offset y * 320 + x. That directness made it ideal for demos, games, and educational experiments. It rewarded people who could reason about memory as geometry. ... continue
Maintenance Is a Creative Act
2026-02-22
In software culture, novelty gets applause and maintenance gets scheduling leftovers. We celebrate launches, rewrites, and shiny architecture diagrams. We quietly postpone dependency cleanup, operational hardening, naming consistency, test stability, and documentation repair. Then we wonder why velocity decays.
This framing is wrong. Maintenance is not the opposite of creativity. Maintenance is applied creativity under constraints. ... continue
Latency Budgeting on Old Machines
2026-02-22
One gift of old machines is that they make latency visible. You do not need an observability platform to notice when an operation takes too long; your hands tell you immediately. Keyboard echo lags. Menu redraw stutters. Disk access interrupts flow. On constrained hardware, latency is not hidden behind animation. It is a first-class design variable.
Most retro users developed latency budgets without naming them that way. They did not begin with dashboards. They began with tolerance thresholds: if opening a directory takes longer than a second, it feels broken; if screen updates exceed a certain rhythm, confidence drops; if save operations block too long, people fear data loss. This was experiential ergonomics, built from repeated friction. ... continue
IRQ Maps and the Politics of Slots
2026-02-22
Anyone who built or maintained DOS-era PCs remembers that hardware conflicts were not rare edge cases; they were normal engineering terrain. IRQ lines, DMA channels, and I/O addresses had to be negotiated manually, and each new card could destabilize a previously stable system. This was less like plug-and-play and more like coalition politics in a fragile parliament.
The core constraint was scarcity. Popular sound cards wanted IRQ 5 or 7. Network cards often preferred 10 or 11 on later boards but collided with other devices on mixed systems. Serial ports claimed fixed ranges by convention. Printer ports occupied addresses and IRQs that software still expected. These were not abstract settings. They were finite shared resources, and two devices claiming the same line could produce failures that looked random until you mapped the whole system. ... continue