从VirualBox 4.2 Beta1 到 VirualBox 4.2 RC4，这时VirualBox最长的一次版本进化，伴随着N多改进，这包括对OS X ML和Win8适配，网络带宽控制，虚拟机分组，剪贴板共享和Drag'n'drop拖拽等期待已久的功能，尤其是Drag'n'drop拖拽，该功能早在六年前[via]，社区就有人提出了，但一直没能实现，其实核心代码早已支持（vbox 是 based on QEMU的），只是Addition需要做些处理。另外，这个版本界面也变得更加美观和实用了。Good Job !
Changelog:
VirtualBox 4.2.0 (released 2012-09-13)
This version is a major update. The following major new features were added:
- Improved Windows 8 support, in particular many 3D-related fixes
- GUI: VM groups (bug #288)
- GUI: expert mode for wizards
- GUI: allow to alter some settings during runtime
- Support for up to 36 network cards, in combination with an ICH9 chipset configuration (bug #8805)
- Resource control: added support for limiting network IO bandwidth; see the manual for more information (bug #3653)
- Added possibility to start VMs during system boot on Linux, OS X and Solaris; see the manual for more information (bug #950)
- Added experimental support for Drag'n'drop from the host to Linux guests. Support for more guests and for guest-to-host is planned. (bug #81)
- Added support for parallel port passthrough on Windows hosts
- Enhanced API for controlling the guest; please see the SDK reference and API documentation for more information
In addition, the following items were fixed and/or added:
- Mac OS X hosts: sign application and installer to avoid warnings on Mountain Lion
- VMM: fixed a potential host crash triggered by shutting down a VM when another VM was running (only affected 32-bit hosts and 64-bit OS X hosts, 4.1 regression, bug #9897)
- VMM: fixed a potential host crash under a high guest memory pressure (seen with Windows 8 guests)
- VMM: improved VM context switch performance for Intel CPUs using nested paging
- VMM: added support for FlushByASID features of AMD CPUs (Bulldozer and newer)
- VMM: fixed unreal mode handling on older CPUs with VT-x (gPXE, Solaris 7/8/9; bug #9941)
- VMM: fixed MP tables fixes for I/O APIC interrupt routing relevant for ancient SMP guests (e.g. old OS/2 releases)
- VMM: support recent VIA CPUs (bug #10005)
- VMM: fixed handling of task gates if VT-x/AMD-V is disabled
- VMM: page fusion fixes
- GUI: network operations manager
- GUI: allow taking screenshots of the current VM window content (bug #5561)
- GUI: allow automatically sorting of the VM list
- GUI: allow starting of headless VMs from the GUI
- GUI: allow reset, shutdown and power off from the Manager window
- GUI: allow to globally limit the maximum screen resolution for guests
- GUI: show the full medium part on hovering the list of recently used ISO images
- GUI: do not create additional folders when a new machine has a separator character in its name (bug #6541)
- GUI: don't crash on terminate if the settings dialog is still open (bug #9973)
- GUI: consider scaled DPI values when display fonts on Windows hosts (bug #9864)
- GUI: if a bridged network interface cannot be found, don't refuse to start the VM but allow the user to change the setting immediately
- Snapshots: fixed a crash when restoring an old snapshot when powering off a VM (bugs #9364, #9604, #10491)
- Clipboard: disable the clipboard by default for new VMs (see the manual for more information). It can be enabled at any time using the VM menu.
- Settings: sanitize the name of VM folders and settings file (bug #10549)
- Settings: allow to store the iSCSI initiator secret encrypted
- NAT: improvements for the built-in TFTP server (bugs #7385, #10286)
- NAT: fixed memory leak when disabling the NAT engine (bug #10801)
- E1000: 802.1q VLAN support (bug #10429)
- Storage: implemented burning of audio CDs in passthrough mode
- Storage: fixed audio CD passthrough for certain media players
- Storage: implemented support for discarding unused image blocks through TRIM for SATA and IDE and UNMAP for SCSI when using VDI images
- Storage: added support for QED images
- Storage: added support for QCOW (full support for v1 and readonly support for v2 images)
- Storage: added readonly support for VHDX images
- USB: don't crash if a USB device is plugged or unplugged when saving or loading the VM state (SMP guests only)
- Solaris additions: added support for X.org Server 1.11 and 1.12
- Solaris additions: switched to using an in-kernel mouse driver
- Windows hosts: no need to recreate host-only adapters after a VirtualBox update
- Windows hosts: updated toolchain; make the source code compatible to VC 2010 and enable some security-related compiler options
- Windows Additions: fixed memory leak in VBoxTray (bug #10808)