HHVM

HipHop Virtual Machine (HHVM) is an open-source virtual machine based on just-in-time (JIT) compilation that serves as an execution engine for the Hack programming language and used to support PHP execution before the release of HHVM version 4.^[6] By using the principle of JIT compilation, Hack code is first transformed into intermediate HipHop bytecode (HHBC), which is then dynamically translated into x86-64 machine code, optimized, and natively executed.^[7][8] This contrasts with PHP's usual interpreted execution, in which the Zend Engine transforms PHP source code into opcodes that serve as a form of bytecode, and executes the opcodes directly on the Zend Engine's virtual CPU.^[9]

HHVM

Developer(s)	Facebook, Inc.
Initial release	December 9, 2011; 13 years ago (2011-12-09)[1]
Repository	github.com/facebook/hhvm
Written in	PHP, C++,[2] OCaml[3][a] and Rust[4]
License	PHP License and Zend License[5]
Website	hhvm.com

HHVM is developed by Facebook, with the project's source code hosted on GitHub;^[10] it is licensed under the terms of the PHP License and Zend License.^[1][5]

Notes

1. Only the Hack's type-checking (hh_server and hh_client) and code-formatting (hh_format) command-line utilities and daemons bundled together with the HipHop Virtual Machine are written in OCaml.