A boot file is essentially a "virtual execution environment": it consists of a memory image containing a number of BCDs that have been loaded but not started. The simple view of MakeBoot is that it takes a collection of specified BCDs, constructs a memory image, and writes it out as a boot file. In practice, however, MakeBoot requires more information than just the names of the BCDs to be included in the memory image; this information is contained in a text file (or files) called the command input. The command input includes a number of parameters that affect the way the boot file is constructed.

The memory image built by MakeBoot is loaded into memory by a simple loader called the germ, which then transfers control to the main body of a module named in the command input. Naturally, there is a certain amount of delicate initialization required to transform the loaded memory image into a running Cedar environment. The details of this initialization include configuration of memory, which, of course, includes dealing with the contents of the initial memory image (boot file) that the germ has loaded. For example, certain portions of the code in the boot file need to be initially resident in main memory, since they will be needed before Cedar's machinery for swapping from disk has been set up. The germ and the Cedar initialization code have to cooperate with MakeBoot to insure that memory residency, and other properties, are preserved during the delicate initialization phase. To do this, they share information contained in the boot file, information which is constructed from the BCDs that make up the memory image and the command input. MakeBoot relies almost entirely on its input for this information; very little is implicitly assumed.

The descriptions below assume certain knowledge of the structure of BCDs, which we summarize here. A .bcd file, which is the output of the Compiler, Binder, or Packager, consists of three related parts: a descriptive portion called the "binary configuration description" (BCD), a (possibly empty) collection of code segments, and a (possibly empty) collection of symbol segments. The descriptive portion includes tables that describe a hierarchy of configurations and the modules they contain, the interfaces imported and exported by the root configuration of the hierarchy, and the packaging of the code and global frames that comprise the modules in the hierarchy. The BCD also describes the location of the code segments and their associated symbols, each of which may be either in the same file with the descriptive portion or in a different one. (There are other, subsidiary tables in the BCD that are not used by MakeBoot.)

This section describes the syntax and semantics of the command input. Many of the possible specifications should be used only upon the advice and counsel of a wizard, since they may cause extremely strange behavior in the initialization or subsequent execution of the boot file. Items of command input that fall in this category have their semantic descriptions preceded by (*).

MakeBoot treats its command input as a linear text stream, which may include white space and comments in the same form and places as Mesa source code. Files formatted for Tioga are also acceptable; any node-structure (other than comments) is ignored. In the syntax equations that follow, white space is not significant and a "|" character denotes metalinguistic alternatives. Words in italics are metalinguistic variables (non-terminals), all other characters appear literally in the command input. (No definitions appear for identifier or non-terminals beginning with decimalNumber; these are presumed to be implicitly understood. Note that, as with all Mesa-related descriptions, the case of alphabetic characters within identifiers is significant.)

gftItem ::= GFT : decimalNumberIn[1..1024] ;

mdsBaseItem ::= MDSBASE : pageNumber ;

codeBaseItem ::= CODEBASE : pageNumber ;

pdaPagesItem ::= PDAPAGES : decimalNumberIn[1..256] ;

framePagesItem ::= FRAMEPAGES : decimalNumberIn[0..256) ;

frameWeightItem ::= frameSpec : fsi , decimalNumber fsiChain ;

nProcessesItem ::= PROCESSES : decimalNumberIn[1..1024] ;

svItem ::= STATEVECTORCOUNT : priority, decimalNumber ;

svSizeItem ::= STATEVECTORSIZE : decimalNumber ;

versionItem ::= VERSION : versionSpec ;
versionSpec ::= major . minor | major . minor . patch
major ::= decimalNumber
minor ::= decimalNumber
patch ::= decimalNumber

ucodeItem ::= ucodeMachine : date ;
ucodeMachine ::= UCODEDORADO | UCODEDOLPHIN | UCODEDANDELION | UCODEDICENTRA

wartItem ::= WART : wartModule ;

residentItem ::= RESIDENT : generalList ;
resDescItem ::= RESIDENTDESCRIPTOR : generalList ;
initiallyInItem ::= IN : generalList ;

controlItem ::= CONTROL : nameList ;

[bootFile: f1, loadMap: f2] ← input[key1: value1, ..., keyn: valuen]/switches