IBM QMS 4525 - Manual (Page 42)

Crown
Multitasking
QMS 4525 Print System User's Guide 2-26
Rather than rasterizing the page as a whole, the Crown operating
system compiles the page into an intermediate, compressed QMS
display list. If the printer is busy printing, the intermediate blocks of
data are stored in printer RAM until the printer is available for printing.
This process allows more efficient storage as well as concurrent com-
piling, rasterizing, and printing. This, in turn, provides faster printing
speeds.
By separating the printing process into the two operations of compil-
ing into an intermediate format and rasterizing, the printer does not
have to re-create an entire page from scratch each time it is printed.
The more time-consuming compilation operation is done only once
per page. Each page may be printed multiple times simply by rasteriz-
ing the intermediate format.
An important feature of compile-ahead technology is simultaneous
compiling, rasterizing, and printing. This capability changes what has
traditionally been a sequential process into a parallel operation where
several processes (compiling, rasterizing, and printing) work indepen-
dently. In other words, the compiler changes the page description into
intermediate blocks and stores them in memory; the rasterizer pro-
cesses the intermediate blocks as needed by the print engine; and
the print engine prints the pages. And all these tasks are done at vir-
tually the same time.
Because the intermediate blocks are compiled ahead, stored effi-
ciently, and processed quickly, after the first copy of a page is printed,
all other copies of that page are printed at the printer's rated speed
and in any order, including being automatically collated. In addition,
parallel operation allows the printer to work on different phases of
several print jobs at one time, employing the print engine more effi-
ciently because it does not have to be turned off between print jobs.
PDL
Compiler
Interprets
PDL and
Creates
Intermediate
Blocks Rasterizer
Rasterizers
Intermediate
Blocks as
needed
Collated
Documents
Intermediate
Blocks
complied
into the
Printer's
Native
Language
(32KB each)
Bitmapped
Pages
as needed
Print
Engine
Prints
Collated
Documents
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