Chain loading: Difference between revisions
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== Chain loading in FORTRAN programs == |
== Chain loading in FORTRAN programs == |
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Many versions of Fortran include a <code>CALL LINK</code> statement that performs chain loading, preserving the contents of COMMON storage.<ref>{{cite book|last=IBM Corporation|title=IBM 1130/1800 Basic FORTRAN IV Language|year=1974|page=14|url=http://bitsavers.trailing-edge.com/pdf/ibm/1130/lang/GC26-3715-8_1130_1800_Basic_FORTRAN_IV_Language_Jan73.pdf}}</ref> This is not the same as the unrelated <code>LINK</code> subroutine in Gnu Fortran.<ref>{{cite web|title=The GNU Fortran Compiler|url=http://gcc.gnu.org/onlinedocs/gfortran/LINK.html|accessdate=Oct 27, 2013}}</ref> |
Many versions of Fortran include a <code>CALL LINK</code> statement that performs chain loading, preserving the contents of COMMON storage.<ref>{{cite book|last=IBM Corporation|title=IBM 1130/1800 Basic FORTRAN IV Language|year=1974|page=14|url=http://bitsavers.trailing-edge.com/pdf/ibm/1130/lang/GC26-3715-8_1130_1800_Basic_FORTRAN_IV_Language_Jan73.pdf}}</ref> This is not the same as the unrelated <code>LINK</code> subroutine in [[gfortran|Gnu Fortran]].<ref>{{cite web|title=The GNU Fortran Compiler|url=http://gcc.gnu.org/onlinedocs/gfortran/LINK.html|accessdate=Oct 27, 2013}}</ref> |
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== References == |
== References == |
Revision as of 12:28, 28 October 2013
This article needs additional citations for verification. (October 2013) |
Chain loading is a method used by computer programs to replace the currently executing program with a new program, using a common data area (a so-called core common area) to pass information from the current program to the new program. It occurs in several areas of computing.
Chain loading is similar to the use of overlays. Like the use of overlays, the use of chain loading increases the I/O load of an application. Unlike overlays, however, chain loading replaces the currently executing program in its entirety. Overlays usually replace only a portion of the running program.
Chain loading in boot manager programs
In operating system boot manager programs, chain loading is used to pass control from the boot manager to a boot sector. The target boot sector is loaded in from disk, replacing the in-memory boot sector from which the boot manager itself was bootstrapped, and executed.
Chain loading in Unix
In Unix (and in Unix-like operating systems), the exec() system call is used to perform chain loading. The program image of the current process is replaced with an entirely new image, and the current thread begins execution of that image. The common data area comprises data such as the process' environment variables, which are preserved across the system call.
Chain loading in BASIC programs
In BASIC programs, chain loading is the purview of the CHAIN
statement (or, in Commodore BASIC, the LOAD
statement), which causes the current program to be terminated and the chained-to program to be loaded and invoked (with, on those dialects of BASIC that support it, an optional parameter specifying the line number from which execution is to commence, rather than the default of the first line of the new program). The common data area varies according to the particular dialect of BASIC that is in use. On BBC BASIC, for example, only a specific subset of all variables are preserved across a CHAIN. On other BASICs, the COMMON
statement can be used in conjunction with CHAIN
to specify which variables are to be preserved as common data across a chain operation.
Chain loading permits BASIC programs to execute more program code than could fit into available program and variable memory. Applications written in BASIC could thus be far larger than the size of working memory, via a set of cooperating programs that CHAIN
back and forth amongst themselves as program flow moves within the overall application.
Chain loading in FORTRAN programs
Many versions of Fortran include a CALL LINK
statement that performs chain loading, preserving the contents of COMMON storage.[1] This is not the same as the unrelated LINK
subroutine in Gnu Fortran.[2]
References
- ^ IBM Corporation (1974). IBM 1130/1800 Basic FORTRAN IV Language (PDF). p. 14.
- ^ "The GNU Fortran Compiler". Retrieved Oct 27, 2013.
- "chain loading". GNU GRUB manual.
- Orlando Lee Stevenson (December 1985). "Commodore Program Chaining". COMPUTE! (67): 114.
- "Security Wrappers and Bernstein Chaining". Taxonomy of Unix IPC Methods.
{{cite web}}
:|chapter=
ignored (help) in The Art of Unix Programming.