Since all Commodore 64 computers were essentially exact copies of each other in terms of hardware, with (almost) all the same glitches, it was possible to write code that took advantage advantage of them and still worked for everyone. Except for this VSP trick, which annoyingly enough seemed to cause random crashes on a large percentage of machines.
This VSP trick made it possible to scroll graphics across the screen in unbelievable speed. If you had ever tried writing a super-optimized machine code routine for scrolling graphics, you'd be absolutely shocked the first time you'd see the speed at which this VSP trick was able to move graphics. And it was extensible in many different ways: it could not only be used to move graphics but also to trick the graphics chip to give more cycles to the CPU, so that you could produce even more stunning and seemingly impossible tricks. So people used VSP, even though it could cause random crashes.
But now, finally, we have an explanation for something that has been bugging a small number of hardcore hackers for decades. And the discovery is by itself the same kind of stunning display of hardcore hackery that made the bug so widespread in the first place.
Ataris had coprocessors for 256-color graphics, sound, I/O, and intelligent peripherals. You could mix text and graphics modes on the screen line by line. They had hardware sprites. The 800 (and its successors) even had an S-video output. All in 1978.
For example, here is a video of the "Super Larrson Brothers" demo: http://www.youtube.com/watch?v=iDMNZa8KjZ4 And here is the code itself: http://www.pouet.net/prod.php?which=51163 it's 170kb and runs on the c64.
One technique used in demos is VSP or "Variable Screen Positioning" which allows for displaying a bitmap at an arbitrary horizontal position, with wraparound, it's used by several demos including the one linked above. However, using VSP can sometimes cause a c64 to crash or lock up, and now the cause of that has been found, enabling workarounds which avoid the problem.
Other common events are 4k and 64k intro compos.
Here's a good example of a larger demo (Lifeforce by ASD): https://www.youtube.com/watch?v=o9GLl6kI4hQ
The size limitation on C64 comes naturally as the disks are only able to store 170kb per side.
Of course that only works when the screen is not divided up into windows. Tricks like these allowed many of the scrolling games on 80 bitters, and are why you could have smooth scrolled text on a 1 MHz cpu with very little software overhead. Even in the PC era these tricks were commonplace on character generator screen modes for lightning fast scrolling. Bitmapped windows are super CPU intensive if you don't have a graphic card that can move around chunks of memory quickly.
C64 modding wikipedia page has more:
VSP (Variable Screen Positioning), also known as HSP,
allows arbitrary x-placement of a bitmap, with the bitmap
wrapping around at the border.
"VSP (Variable Screen Positioning), also known as HSP, allows arbitrary x-placement of a bitmap, with the bitmap wrapping around at the border."
If they had been working on this for 30 years, I could only imagine the joy and exhilaration of squashing this bug...
The "dram"? Meaning a unit of volume? : http://en.wikipedia.org/wiki/Dram_(unit)
Or did the author mean "DRAM", i.e. dynamic random access memory? Somehow I think the second meaning was intended, in which case, as an acronym, ALL CAPS is required.
The scroll itself in the intro is in all-caps, i.e. all the text is shown as caps.
Also, I really think context makes it fantastically clear here that it's talking about aspects of computer hardware.