"I can't tell what PERC I have in my 6850 (new 800MHz motherboard).  The old 6850 and transplanted key were 4e/di.  The new one might be too, but something led me to believe it was a 5/i.  How can I tell?  The LSI chip on the board appears identical to the old 4e/di motherboard.  I remember now.  When I type in my service code it reported I had the 5/i.  Do the 5/i and 4e/di use the same LSI chip?" All 6850's have an embedded/integrated PERC 4e/Di (when the RAID key/DIMM are installed - it must also be enabled in the BIOS).  You could have a PERC 5/i card, but that would be an add-in PCIe card and not the onboard/integrated/embedded controller.  Also the PERC 4 is for SCSI drives only, and the PERC 5 is for SAS/SATA drives only.  The PERC 4 has a CTRL-M prompt to enter its configuration utility, and the PERC 5 has a CTRL-R prompt for its utility.  Again, you DO have a PERC 4, but you MIGHT ALSO have a PERC 5.  You cannot use both simultaneously, however. "The OS is Windows 8.1 Pro x64 on two CPUs.  I know that's not supported, but this is a hobby server so trying to solve problems is what its for.  I'm willing to upgrade to Windows 7 Pro x64 if that makes finding a driver easier.  I don't want to run a server OS because I plan to game, but I do have access to them.  What is the most advanced Windows Server OS that I can install?" Dell does not have any "signed" drivers for any client OS's (Windows X/V/7/8/8.1), however, because Windows 2003/2008/2008R2/2012/2012R2 use the same kernel as the corresponding client OS, the driver will "usually" work (including the signature).  So, when installing a client OS, the best thing to try (not, however, guaranteed to work) is the corresponding Server driver version.  In the case of Windows 8.1, Dell does NOT have a 2012R2 driver for the PERC 4e/Di (or the 6850 in general) - and they probably never will - they likely have dropped ongoing OS support for 8G systems.  You "might" be able to get it working with a PERC 5, as the drivers for that controller will be native to 2012R2, but you may have issues with other hardware. Others have reported being unable to get 2012R2 installed on the 6850's cousin, the 2850 - I have not tried, so I'm not sure if there is a workaround or a way to get it working - but it is likely that 2012R2 will not run on a 6850 with a PERC 4 at all.  I have had Server 2012 running on a 2850, however, using 2008R2 drivers.  It does not run as well as 2008R2. 2008R2 is the latest stable/supported OS on the 6850.  The corresponding client OS is Windows 7x64.  Like I said, you "might" be able to install 2012/Windows 8, but it probably won't run as well.  Since you have SCSI drives, you likely won't be able to use 2012R2/Windows 8.1 at all. Because Windows 7 drivers do not exist, you will need to use 2008R2 drivers (2008x64 for the video, as they seem to have been overlooked by Dell - the display is horrible without it). Also keep in mind that the server would only be good for gaming if all it does it crunch numbers ... the graphics is limited to like 16MB of video RAM, and the server doesn't support graphics cards.  Gaming directly on the 6850 wouldn't work, but as a gaming "server", as long as it is only required to crunch numbers or manage network connections - and not do any video output - it should be fine.  Servers are powerful, but they make lowsy gaming systems. "OS is Windows 8.1 Pro x64 on two CPUs" So, your 6850 only has 2 of the 4 processor slots populated? "What is the equivalent LSI product and are those drivers better?" I don't remember, and I didn't look it up, because I know that LSI does not have as recent of drivers for the LSI equivalent as Dell does (I think XP/2003 is the latest LSI offers for the PERC 4 equivalent).
I'm looking for a Signed Driver for the PERC 5/i.  This is built into my 6850, but may be the same as the 2950.  Willing to give either a try.  I'm installing a Windows OS that is asking for the signed driver, without which it can't see the hard drives.
PERC 5/i Signed Driver - PE 1950 PE 6850 SAS SCSI