Editing Machine code (section)

==Notes==
{{reflist|group="nb"|refs=
<ref group="nb" name="NB_DR-DOS_707"> For example, the [[DR-DOS]] [[master boot record]]s (MBRs) and [[volume boot record|boot sectors]] (which also hold the [[partition table]] and [[BIOS Parameter Block]], leaving less than 446<!-- MBR --> respectively 423<!-- 512-87-2 (ignoring the 3-byte-jump which can also be counted as code) in the case of FAT32, a bit more with FAT12/FAT16 --> bytes for the code) were traditionally able to locate the boot file in the [[FAT12]] or [[FAT16]] [[file system]] by themselves and load it into memory as a whole, in contrast to their counterparts in [[MS-DOS]] and [[PC DOS]], which instead rely on the [[system file]]s to occupy the first two [[directory entry]] locations in the file system and the first three sectors of [[IBMBIO.COM]] to be stored at the start of the data area in contiguous sectors containing a secondary loader to load the remainder of the file into memory (requiring [[SYS (DOS command)|SYS]] to take care of all these conditions). When [[FAT32]] and [[logical block addressing]] (LBA) support was added, [[Microsoft]] even switched to require [[i386]] instructions and split the boot code over two sectors for code size reasons, which was no option to follow for DR-DOS as it would have broken [[Backward compatibility|backward]]- and cross-compatibility with other operating systems in [[multi-boot]] and [[chain load]] scenarios, and as with older [[IBM PC–compatible]] PCs. Instead, the [[DR-DOS 7.07]] boot sectors resorted to [[self-modifying code]], [[opcode]]-level programming in machine language, controlled utilization of (documented) [[side effect (computer science)|side effect]]s, multi-level data/code overlapping and algorithmic [[Fold (higher-order function)|folding]] techniques to still fit everything into a physical sector of only 512 bytes without giving up any of their extended functions.<!-- and adding some more --></ref>
<ref group="nb" name="NB_Merging_or_branching">While overlapping instructions on processor architectures with [[variable-length instruction set]]s can sometimes be arranged to merge different code paths back into one through control-flow [[self-synchronizing code|resynchronization]], overlapping code for different processor architectures can sometimes also be crafted to cause execution paths to branch into different directions depending on the underlying processor, as is sometimes used in [[fat binaries]].</ref>
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