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apple-pascal-1.3-manual

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Figure 1-3. The Pascal 128K System: Auxiliary MemoryAuxiliaryMemoryReservedforSystemUse1/0 DeviceAddresses & ROMsPart of theOperating SystemP-code(builds down)r---------------- •Free Memory..,.. __ CODEP$FFFF64K$DOOO 52K$00000 48KText ScreenSystem Use$0800 2K$0400 lK$0000 OKThe principal difference in memory usage between the 64K and 128K ApplePascal systems is this. In the 64K system, a single area of free memory isused by P-code, 6502 code, and data. In the 128K system there are two areasof free memory; one is used only by P-code, and the other is used only by6502 code and data.Here are some additional points about memory usage to supplement theinformation in Figures 1-1, 1-2, and 1-3:o In both systems, pointer NP points to the top of the heap space. PointerKP points to the top of the program stack. In the 64K system the stackcontains P-code, 6502 code, and data; in the 128K system it contains only6502 code and data. In the 128K system another pointer, CODEP, pointsto the top of the area used by P-code. The locations of these pointers aregiven below under "Useful Memory Addresses."o The beginning of the heap ($0800) is shown for 80-column mode. In40-column mode the heap starts lK higher, at $0COO.System Memory UseIV-5

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