For the last 5 years, my system has had 8gb of ballistic ram (ddr3 1600mhz CAS 9) (2x4gb). I found some extra Samsung 4gb sticks lying around (ddr3 1600mhz CAS 11) and decided to throw them in there. Upon booting into windows the system only recognized 8gb. So I checked bios and the motherboard is only reporting 8gb available memory but does detect that all 4 slots have 4gb memory sticks in them. So then I decided to check each stick individually in each slot and the system booted without failure. I can mix and match ram pairs too, 1 ballistic in a1 or a2 and 1 samsung in b1 or b2, the system boots fine and even indicates dual channel mode is active. But for some reason, it only recognizes RAM in slots a1b1 or a2b2 when all 4 slots are taken. I tried inserting only 3 sticks but once again it only recognized 2.
Has anyone ran into this issue before? I looked into the mobo manual and it says to use ram slots in pair a1b1 or a2b2 when using only 2 sticks and to use identical sticks. Here I can mix and match RAM but only a max of 2 get detected. I have updated my bios and cleared CMOS but nothing seems to get the system to utilize more than 2 slots. The system has also never failed to boot.
Specs
Windows 10 pro
Asrock a77 Extreme 4
i5-3570k
gtx 970
CX750m
240GB crucial ssd
1tb WD blue
2 4gb ballistic
2 4gb samsung
Update: After a few hours of searching I found a couple of other posts with the same issue from a few years ago. They never found any resolution. I messed with the voltages and speeds but no luck. It appears some z77 boards only recognized 2 dimm slots either a1b1 or a2b2, they would never use 4 at once. Very frustrating.