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Dale - Computer Science Illuminated 229

Dale - Computer Science Illuminated 229 - virtual machine...

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Loader A piece of soft- ware that takes a machine language program and places it into memory 202 Chapter 7 Low-Level Programming Languages recognizes two z ’s as the end of the program. Here is a screen shot of the Pep/7 machine-language program, followed by a screen shot of the output window. Let’s go through the steps required to go from the algorithm to the output. We assume that the Pep/7 simulator has been installed. We begin by opening a new file into which we enter our program. The File menu on the menu bar allows us to do this. The menu bar looks like this: We then key in the program as shown above and save the file, thus giving it a name. The next step is to load this program into the memory of the Pep/7
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Unformatted text preview: virtual machine and execute it. Under the Pep7 pull-down menu, there are several options. The second is Load , the one we need. When Load is clicked, a piece of software called the loader takes the program and loads it into memory beginning in location 00000. Here is what Pep/7’s memory looks like when the loader has finished. Although memory is one long stream of bytes, we show it here in groups of three because each instruc-tion except the Stop instruction takes three bytes. 11 1 1! 19 1R 1F Address )1 )1 )1 )1 )1 11 11 11 11 11 11 C> !O !R !R !F...
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