Added a total 12GB RAM to laptop, but only 3.2GB is usable

Your Pavilion 15z-e000 Series System Specs

Memory Type: DDR3 PC3-12800, DDR3 PC3-14900, DDR3 (non-ECC)
Maximum Memory: 8GB 
Slots: 2

Generally, the maximum size for each slot is the maximum ram divided by the number of slots (in this case 4GB). Since you've purchased 12GB of ram for 2 slots, I'm going to guess one of those is a 8GB module. You can't use an 8GB module in a slot that only supports up to 4GB.

I was under the impression that most computers will just disregard the rest of the ram within the module, so that it's still compatible. But unfortunately, that doesn't seem to be the case with your computer. I would suggest returning the ram to the store you bought it at (ASAP) and purchasing a 4GB module instead.

Next time you purchase ram, keep in mind that the memory you buy is determined by:

CPU: not all x64 CPUs support the same amount of ram, even though they mostly support 32GB
Motherboard: Even with x64 CPUs, you may only be able to have, ie, 8GB on your motherboard (this, more specifically, is a limitation of the memory manager and number of slots on your MOBO). Your motherboard also determines how fast the RAM can run (but this isn't suppose to affect compatibility).
OS: there are 64b and 32b versions of almost every operating system, and it doesn't just mean 4GB vs inifnite GB. Look up your OS and find out how much ram you can add (32b versions of Windows will actually be limited to 3.5GB or 3GB).

tay10r

Posted 2013-08-07T00:19:41.043

Reputation: 533

332-bit versions of Windows are actually limited to 3.5GB, so when I first saw the title of this question that was the first thing I thought of. The OP just said "Windows 8", not indicating bitness, so that could still be it... but I suspect that you're right about the 8GB module not being usable. – MT_Head – 2013-08-07T05:15:16.793

@MT_Head your right, I forgot about that. But I did look up the computer, and it does come with the 64b version of Windows. – tay10r – 2013-08-07T21:34:47.637

1I'm pretty sure you're right: the OP says "It shows that I'm using less ram after the upgrade than before", which says (to me) that the machine was reporting more than 3.2 GB before. I seem to have muddied the waters with my comment; I just wanted to say that the title (if not the actual text) of the question makes this look like a bitness issue. At first glance, anyway. – MT_Head – 2013-08-07T21:48:41.830

@MT_Head yeah it definitely does – tay10r – 2013-08-07T21:50:07.753

Generally, the maximum size for each slot is the maximum ram divided by the number of slots Generally (or not). The motherboard manual will (or should) say for sure. – Synetech – 2013-09-24T23:05:18.287

Added a total 12GB RAM to laptop, but only 3.2GB is usable

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