VirtualBox 4.1.0 Beta 2

VirtualBox is a general-purpose full virtualizer for x86 hardware. Targeted at server, desktop and embedded use, it is now the only professional-quality virtualization solution that is also Open Source Software.

Some of the features of VirtualBox are:

Modularity. VirtualBox has an extremely modular design with well-defined internal programming interfaces and a client/server design. This makes it easy to control it from several interfaces at once: for example, you can start a virtual machine in a typical virtual machine GUI and then control that machine from the command line, or possibly remotely. VirtualBox also comes with a full Software Development Kit: even though it is Open Source Software, you don't have to hack the source to write a new interface for VirtualBox.
Virtual machine descriptions in XML. The configuration settings of virtual machines are stored entirely in XML and are independent of the local machines. Virtual machine definitions can therefore easily be ported to other computers.

Changelog:

# New features were added
* GUI: keep the aspect ratio in scale mode (Windows and OSX hosts only)
* Experimental support for PCI passthrough for Linux hosts, see Section 9.6, “PCI passthrough”
* Networking: new network attachment mode "Generic Driver", which offers an open plugin architecture for arbitrary and separately distributable virtual network implementations
* Experimental support for SATA hotplug added. Currently only supported for hard disks and only with VBoxManage.

# The following items were fixed and/or added:

* GUI: decrease time before showing the VM configuration dialog
* Settings: provide better diagnostics if a single medium is used twice in a VM config
* Settings: provide better diagnostics for errors in medium create/merge/clone operations, and fix memory leaks in error cases
* Storage: ATA/SATA drives can be marked as non-rotational, i.e. the guest OS will detect them as a SSD if supported, which can improve performance
* Storage: virtual CD/DVD images will be detached if the guest ejects the medium, unless the drive is marked to handle ejects only on a temporary basis
* Storage: the medium UUID can be changed again when attaching a medium for the first time, which allows using images which are exact duplicates including the UUID
* Storage: fixed possible data corruption under certain circumstances with VHD and Parallels images
* Storage: fixed unnecessary expansion when cloning differential images in VDI format
* Storage: fixed detection code to handle empty files for VDI and VMDK format
* Floppy: make it possible to unmount a host floppy disk
* Networking: workaround for a bug in wireshark when operating directly on a capture file created by VirtualBox
* Webservice: fixed timeout handling with HTTP 1.1 keepalive, and be more robust when connections fail
* VBoxSVC: fixed regression when several clients trigger autostart simultaneously
* Main: fixed incorrect handling of the medium location for media which are not file based (e.g. iSCSI), which resulted in confusing location values in many places
* JAX-WS client bindings: fixed resource leak
* Sources: fixed USB 2.0 support using extension packs for non-official builds
* Windows hosts (64-bit only): enabled removing of all mediums when removing a VM
* Windows hosts (64-bit only): enabled live snapshot deletion
* Solaris Additions: fixed automounting of shared folders