The different types of loading bars on the Commodore 64
A characteristic of loading on the Commodore 64 was the presence of horizontal bars on the screen (loading bars), which were inserted specifically by the programmers to give information on the loading progress of the games. For example, no bars meant that the software was still looking for data, while the presence of bars indicated the data was successfully loaded into memory.
The shape or color of the bars gave useful information, for example if the multicolored bars were not uniform meant that the datatape head had to be aligned, or in the case of monochrome or edge bars on the monochrome screen, these changed color depending on the data block that was going to be loaded and therefore indicate that every single block of data was loaded successfully into the memory of the Commodore 64.
In some cases there was also a counter on the screen that indicated the progress of the loading, in some other cases instead there was an image of the game at the center of the screen, with the moving colored bars at the sides, and this image could also be accompanied by music. In rare cases, during loading was shown a clone of Space invaders that could be played during the data upload.
The colored bars effect was created thanks to the fast alternation of screens of different colors which added to the interlaced scan gave the effect of bars, and their thickness was a function of the frequency with which the screens of different colors alternated. Basically, after executing a block of instructions, the program sets the background color to a certain value: since it is done while the raster draws the video, the color changes many times while the raster scrolls the screen, and this generates the bars.
The programmers also exploited these bars to understand where there was an error in the code: if the program went into error during loading, it could be traced back to the last instruction block executed through the shown last background color before error.
The colored bars were horizontal and not vertical because it was impossible for the hardware to produce vertical lines so thin, and this by how the raster works: the video signal is originated progressively along a cursor that starts from the top left corner and runs horizontally along each directional line to the right, scrolling the entire screen until it reaches the bottom right corner.
The color of each line changes with each change of state of the pulses, consequently the thickness of the line ends up being proportional to the duration of each impulse, and therefore have been practically impossible to produce thin vertical lines of the same aspect, because both the frequency of the pulses given and the speed of the processor would not have allowed changing the color of the border so quickly several times while the raster is still in the same row.
Note: The bars that were used to inform the user of the correct loading were born with the Sinclar ZX81 and had more the form of "interferences" which anyway could give information on the correct data loading according to their amplitude. In the most recent Sinclar systems, actual loading bars were directly encoded in the machine's ROM memory. The slow and thick cyan and red bands indicated the search of the pilot signal for the data, while thin blue and yellow bands indicated the loading of blocks of data in memory. The thinner the band, the faster the data transmission speed. Obviously it was also possible to change the color of these colored bars.
Following are shown different types of loading bars that could be found in the game loading screen of Commodore 64 games.
Loading bars with a presentation image
Loading screens with game
Loading screens with counter or simple text
Loading bars with different thickness on the Commodore 64
source: infogiochi.altervista.org
