Re: Printer buffer: does size matter?
- From: David Lloyd Geering <dreamlax@xxxxxxxxxxxx>
- Date: Fri, 02 Dec 2005 09:30:29 +1300
Robert Heller wrote:
"Dan" <luecking@xxxxxxxx>, In a message on 1 Dec 2005 09:04:01 -0800, wrote :
"> Patrick TJ McPhee wrote:
"> > In article <1133380521.528551.229590@xxxxxxxxxxxxxxxxxxxxxxxxxxxx>,
"> > Dan <luecking@xxxxxxxx> wrote:
"> > % To be able to print a file, the printer needs enough memory to generate
"> > % one scan line for the laser.
"> > To be able to print a page, a laser printer needs enough memory to
"> > generate the page. This can be a lot or a little depending on how
"> > the page is created. e.g., a page of text using printer fonts will
"> > require little memory, while a page of layered graphics might
"> > require a great deal.
"> "> I was speaking theoretically. I have no idea what the actual practice
"> is. But I would consider a printer badly designed if it had no way to
"> handle partial pages in its memory.
"> "> My understanding is that a laser is used to alter the surface of a
"> rotating drum and when the drum has an entire page, it is used to
"> transfer toner to paper. *If * the laser does the writing to the drum
"> a line at a time the printer *could* retrieve one line from the buffer
"> and, while sending that line to the drum, another *could* be sent to
"> the buffer (dot matrix printers would do the analogous thing directly
"> onto paper and get by with very small memory).
"> "> I do know that I have printed a full page graphic on printers with less
"> than 1MB of memory so there would seem to be some strategy to receive
"> less than a page at a time, or perhaps some compression scheme. In my
"> experience, almost never do printers just refuse (except some
"> postscript printers -- where any part of the PS code can alter any part
"> of the page), though often they slow down drastically.
Generally, a *laser Postscript* printer has a screen buffer, internal working memory (for the postscript stacks, dictionaries, etc.), plus an input buffer (fifo connected to the I/O port). At least this is what it *logically* needs to have. Generally, the PostScript 'engine' is running on some sort of embedded processors (some early models had a 68000 processor). This processor runs a program something like ghostscript. How this relates to the 'buffer size' in the specs is not clear and probably depends on how the internal processor's memory is arranged. It could be that the 'screen buffer' is like video RAM - it is not counted as part of main memory. Also the 'buffer' can be just the memory directly connected to the I/O port, and the main memory and 'video RAM' are counted separately.
I don't think a *Postscript* can generate one scan line at a time -- the Postscript language is 'random access' and can draw stuff all over the page in any random order. A whole 'page' has to be buffered somehow.
Inkjets all do one head's worth of scans line at a time and when converting from postscript to inkjet, generally via GhostScript, the conversion program (GhostScript) has the page buffer in host computer memory, which is then written line by line to the printer (via a pipe or a file).
"> "> "> Dan
Robert Heller ||InterNet: heller@xxxxxxxxxxxx
http://www.deepsoft.com/ ||FidoNet: 1:321/153 http://www.deepsoft.com/~heller /\
A 600 d.p.i. monochrome laser printer would only require a single bit of memory for each possible dot on the page. Pretend we are printing on A4 at 600 d.p.i (for consistency we will stick with Imperial).
A4 is 11.7 inches in height and 8.25 inches in width. At 600 d.p.i., that equals 7020 dots high and 4950 wide. These multiplied give 34,749,000. Divide that by 8 * 1024 ^ 2 to get roughly 4.14 megabytes. This is assuming the printer can print right to the very margins of the page. Wouldn't it require at least this much memory to print a full-page graphic?
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