We are using Sitecore 8.1 Upd 3. However, as this version has been discontinued at the end of 2018, I started considering upgrading to the latest Sitecore 9.1.
Referring to Sitecore's compatibility table, in 8.1 and 9.1, in all of OS / SQL / Mongo / Solr, I found that a different version is required.
In addition, the site we operate is on the virtual server on IaaS, and it is not easy for users to upgrade the OS, I can not assume it.
Our environment is follows
Sitecore 8.1 Update 3 OS Windows Server 2012 R2 SQL SQL Server 2012 Mongo 3.0 Solr 4.1
Is it possible to upgrade Sitecore from 8.1 to 9.1 without upgrading the OS (Windows)?
Is it possible to run Sitecore 8.1 with OS / SQL / Mongo / Solr version adapted to the requirements of 9.1?
I hope you will receive wisdom.