What is bootstrapping?

Question

"Bootstrapping" comes from the term "pulling yourself up by your own bootstraps." That much you can get from Wikipedia.

In computing, a bootstrap loader is the first piece of code that runs when a machine starts, and is responsible for loading the rest of the operating system. In modern computers it's stored in ROM, but I recall the bootstrap process on the PDP-11, where you would poke bits via the front-panel switches to load a particular disk segment into memory, and then run it. Needless to say, the bootstrap loader is normally pretty small.

"Bootstrapping" is also used as a term for building a system using itself -- or more correctly, a predecessor version. For example, ANTLR version 3 is written using a parser developed in ANTLR version 2.

An example of bootstrapping is in some web frameworks. You call index.php (the bootstrapper), and then it loads the frameworks helpers, models, configuration, and then loads the controller and passes off control to it.

As you can see, it's a simple file that starts a large process.

The term "bootstrapping" usually applies to a situation where a system depends on itself to start, sort of a chicken and egg problem.

For instance:

• How do you compile a C compiler written in C?
• How do you start an OS initialization process if you don't have the OS running yet?
• How do you start a distributed (peer-to-peer) system where the clients depend on their currently known peers to find out about new peers in the system?

In that case, bootstrapping refers to a way of breaking the circular dependency, usually with the help of an external entity, e.g.

• You can use another C compiler to compile (bootstrap) your own compiler, and then you can use it to recompile itself
• You use a separate piece of code that sets up the initial process without depending on any functions provided by the OS
• You use a hard-coded list of initial peers or a hard-coded tracker URL that supplies the peer list

etc.

See on the Wikipedia article on bootstrapping.

There is a section and links explaining what it means in Computing. It has four different uses in the field.

Here are some quotes, but for a more in depth explanation, and alternative meanings, consult the links above.

"...is a technique by which a simple computer program activates a more complicated system of programs."

"A different use of the term bootstrapping is to use a compiler to compile itself, by first writing a small part of a compiler of a new programming language in an existing language to compile more programs of the new compiler written in the new language."

In the context of application development, "bootstrapping" usually comes up when talking about modular and/or auto-updatable software.

Rather than the user downloading the entire app, including features he does not need, and re-downloading and manually updating it whenever there is an update, the user only downloads and starts a small "bootstrap" executable, which in turn downloads and installs those parts of the application that the user needs. Additionally, the bootstrap component is able to look for updates and install them each time it is started.

Alex, it's pretty much what your computer does when it boots up. ('Booting' a computer actually comes from the word bootstrapping)

Initially, the small program in your BIOS runs. That contains enough machine code to load and run a larger, more complex program.

That second program is probably something like NTLDR (in Windows) or LILO (in Linux), which then executes and is able to load, then run, the rest of the operating system.

For completeness, it is also a rather important (and relatively new) method in statistics that uses resampling / simulation to infer population properties from a sample. It has its own lengthy Wikipedia article on bootstrapping (statistics).