Sync scrolling
An Atari ST trick that fools the video chip into making scanlines longer or shorter than normal, shifting the whole screen without copying a single byte.
The original Atari ST had no hardware scrolling: the screen base address could only move in 256-byte steps, and pushing 32 KB of graphics around with the 68000 every frame ate the CPU alive. Around 1990, demo coders found that flipping between 50 and 60 Hz, or between low and high resolution, on exactly the right clock cycle made the Shifter fetch more or fewer bytes for a line. A few tampered lines at the top offset everything below them.
Combine enough line lengths and you can reach any start address, so the screen scrolls smoothly for almost nothing. Thalion's Enchanted Land (1990) proved the technique worked in games too. The STE added real scroll registers, making the trick unnecessary on a model few people owned.