Made minor changes.

Added details about the OS X x86-64 environment.

Added details about the user-space code model in x86-64 Code Model.

Added details about symbol references to x86-64 Symbol References.

Added details about symbol relocations in Relocations in the x86-64 Environment.

Added information on the IA-32 symbol stubs and the DWARF debugging format.

Added information about the DWARF debugging format to Scope and Treatment of Symbol Definitions.

Added information on the stubs used for indirect addressing in the IA-32 environment in Indirect Addressing.

Added the "Dynamic Code Generation" article from content previously published in "PowerPC Runtime Architecture Guide."

Clarified terminology for binaries that contain object files for more than one architecture.

Updated for OS X v10.4.

New document that describes basic concepts about the OS X runtime environment. Replaces information that was published previously in "Mach-O Runtime Architecture."

Corrected sample of a private external symbol in Scope and Treatment of Symbol Definitions in Executing Mach-O Files.

Corrected framework-building example in Listing 1.