20 Mem Overflow and 21 Print Overrun errors when printing to PCL printers
Note: Some of this information may be a bit out of date, but if you see these specific errors, it's worth reading this over.
You get a 20 Mem Overflow and 21 Print Overrun errors when printing
If you print complex work to a printer that uses the PCL printer control language (most HP printers, many other laser printers), you may see one of these error messages, especially if your printer has limited memory. The printer manual, if there is one, probably says to reduce the complexity of your page or to add more memory.
There are a few printer tweaks that can help
20 and 21 errors are both memory-related. Let's look at how the printer uses memory (RAM) and how you can help it maximize the available RAM to print your pages.
The ability to do convert PCL to printer dots is built into the printer's software, which needs memory to play in. The printer reserves a chunk of RAM for the software itself. There's nothing you can do to change that, so we'll ignore it, other than mentioning that the total amount of memory in your printer isn't available for the stuff we'll describe next.
More memory goes to hold fonts, macros and data as it comes in from your computer. The printer allocates this memory flexibly, but once you've used it, it's unavailable until you reset the printer or clear the fonts and/or macros from memory.
Finally, the printer uses any RAM that's left as a "holding tank" for rasterized data (ie, printer dots).
That's where things get interesting. The printer can handle this portion of memory in two very different ways; you get to tell it which to use by changing the printer's Page Protection setting.
If Page Protection is ON, the printer reserves enough memory for a full page of graphics at the current resolution and page size. Since it can then hold a complete page in memory, if the printer jams, it can immediately reprint the page after you clear the bits of crumpled paper out of the innards.
Here's the rub: for a letter size page at 300 dpi, it takes a little over a megabyte of RAM to store the whole page image; make that four megs at 600 dpi, lots more at 1200 dpi and up. If you have only the minimum amount of memory that comes with the printer, you may see 20 MEM OVERFLOW errors if you try to print a complex page.
This message means that your page has used up all the available RAM.
To solve 20 MEM OVERFLOW error problems, you could always set the printer to a lower resolution and try printing again, but after paying the big bucks for high rez, who wants to print at 150dpi?
Instead, try turning Page Protection OFF to reclaim the chunk of memory it was holding out on you. That will probably get the paper flowing again, but there's a new problem lurking there behind the printer's message panel: 21 PRINT OVERRUN.
With Page Protection OFF, the printer can't assemble the whole page in memory before committing it to paper. Instead, it starts transferring the image to paper a band at a time as soon as it starts receiving data from the computer.
So long as it can get each band of dots ready in time, no problem, but the more complex the image, the longer it takes to process it. In this context, "complex" means "lots of stuff to convert to dots, all in a small space". A good example would be long lines of tiny text closely spaced.
If the printer can't keep the pixels flowing as fast as the paper is moving, you'll get a 21 PRINT OVERRUN error. The fix is to turn Page Protection ON.
It's a tradeoff. Images with a lot of data will eat up a lot of memory, so reclaiming some RAM from Page Protection may help. On the other hand, very complex images may not be so RAM-hungry, so turning Page Protection ON might work, and will prevent a 21 error.
You may be able to make the 21 errors go away, only to be plagued by 20 errors from the same print job. This shouldn't be too surprising, since you're robbing Peter to pay Paul ... taking the same amount of memory and allocating it differently.
If you can't get rid of the one without causing the other, you may have to do what the manual said in the first place: simplify your pages or plunk down the plastic and buy more RAM for your printer.