Microsoft assigns vendors the altitude for a filter driver operating in the Windows environment. The altitude determines load order groups for file system filter drivers and legacy filter drivers. For more information, see this Microsoft article.

Our drivers use decimal values, intentionally, and with Microsoft's consent. Although it's uncommon to encounter drivers with decimal values in the field, it's nonetheless permissible and expected behavior for our drivers.

The use of decimal values enables driver upgrades to occur and reduce if not avoid an immediate need for reboot, post upgrade. The use of decimal values also avoids an immediate need for reboot on fresh installations when the driver technology is shared with another product. The driver with a decimal value most commonly encountered is mfehidk.sys, a minifilter driver. The following is an excerpt from the Microsoft article:

"A minifilter driver can be loaded at any time. The concept of load order groups is still required by minifilter drivers for interoperability with legacy file system filter drivers. Every minifilter driver must have a unique identifier called altitude. The altitude of a minifilter driver defines its position relative to other minifilter drivers in the I/O stack when the minifilter driver is loaded. The altitude is an infinite-precision string interpreted as a decimal number. A minifilter driver that has a low numerical altitude is loaded into the I/O stack below a minifilter driver that has a higher numerical value."

The whole-number part is pre-assigned. The suffixes .00 through .99 deal with upgrade scenarios where a new filter version must coexist with a previous one until you reboot your computer. This use is consistent with the Filter Manager's own method of dealing with legacy filters.