I got the 750mb update as well. Installed it. It was a cumulative update: KB3000850. Not firmware/system hardware. Support page describes the update:
This update rollup includes the following new features and improvements:
- Refreshed language packs
- Defence-in-depth security and Schannel hardening
- Support for newer hardware (boot order allowance, SD card improvements, USB debugging)
- Improved Web Services for Devices (WSD) printer support during network switches
- Performance and reliability improvements in clustered virtual machine mission-critical environments
- Improved manageability
- Additional hardware support (devices that have third-party disk encryption software enabled can now be upgraded to Windows 8.1 more easily)
This November update rollup also includes all previous updates since our last image update in April 2014. This is a convenient single step to bring Windows clients and servers up to date. Unlike our April update, the November update rollup is not required to be able to continue to receive security or other updates. However, we strongly recommend that you deploy it to Windows clients and servers to benefit from these new features and improvements as well as to prevent many known issues that have been resolved since April. This update is thoroughly tested to the same quality level as our previous service packs. However, unlike service packs, this update does not change the version number and does not deprecate or change any APIs in a manner that would require recertification.
