Why is my Bios reserving 513mb of ram?

[koo_weaver]

Been having this issue since upgrading to windows 7 ultimate 64bit. I first noticed after installing it that it wasn't even recognizing the full 4 gigs, like a 32bit would do. But went into my bios and found that it isn't recognizing it either. So I re-flashed my bios, and boom like magic, problem fixed. This was about a week ago. For the last couple of days it says 3.5 gigs usable, so I started looking for a cause. I didn't find a clear answer. So Shutdown the PC for the night, next morning, it shows a full 4 gigs!!!!!!! But today it says bios is reserving 513mb, why and is this changeable?
OS Name Microsoft Windows 7 Ultimate
Version 6.1.7601 Service Pack 1 Build 7601
Other OS Description Not Available
OS Manufacturer Microsoft Corporation
System Name WEAVER-PC
System Manufacturer Acer
System Model ASE380/AST180/APM8
System Type x64-based PC
Processor AMD Athlon™ 64 X2 Dual Core Processor 4200+, 2210 Mhz, 2 Core(s), 2 Logical Processor(s)
BIOS Version/Date Phoenix Technologies, LTD R01-C0, 6/15/2007
SMBIOS Version 2.3
Windows Directory C:\Windows
System Directory C:\Windows\system32
Boot Device \Device\HarddiskVolume1
Locale United States
Hardware Abstraction Layer Version = "6.1.7601.17514"
User Name Weaver-PC\Joel&Jessi
Time Zone Eastern Daylight Time
Installed Physical Memory (RAM) 4.00 GB
Total Physical Memory 3.50 GB
Available Physical Memory 1.97 GB
Total Virtual Memory 7.00 GB
Available Virtual Memory 5.27 GB
Page File Space 3.50 GB
Page File C:\pagefile.sys
the above is pasted from system information screen. If you want a more in depth let me know. Also I am not using the onboard graphics, I have a AMD HD 6670 installed.

update:
I have been working on this extensively since I posted it. I have searched, and searched... and searched. I haven't really found anything, I tried some ideas people had with half there ram being reserved by bios. So, one problem is bios won't recognize a full 4gigs unless I either flash bios or just pull the battery out. BUT!!!!, after I post and then reboot, I am back where I started. Except for this very instance bios is only reserving 498mb for some reason, great, grand, wonderful. I am lost, if it isn't obvious, lol. Anyone got ANY ideas, at this point I am all hears for even the most absurd.

I think I would like to take this moment to commend everyone on this site, since finding it a year ago, it has been a vast resource worth it's weight in gold and I thank you.

[koo_weaver]

Just a quick thought
I know that the onboard graphics chews memory, which makes since. But it is uninstalled from my computer and has been since I got the above mentioned card and does appear in the device manager as it shouldn't. But can it still be taking away memory?

[koo_weaver]

Well figured it out. On my own too, so I feel pretty good about it. Anyways... After messing around in BIOS and pulling the bat again (and nicking the tip of my finger somehow which wouldn't stop bleeding, lol). I opted out of disabling "AUTO OPTIMIZE BOTTOM OF IO". I never really had a understanding of this feature and still don't. When I was running vista 32bit, I played with disabling it, and there is a another menu below it that unlocks and you can set a hexadecimal value between 00 and ff, I used different values and got it in mind that it was impacting the frequency of my memory. But this time with it enabled only 2mb of ram is reserved for bios and it did not change my memory freq. So, I tried googling this bios feature and really found nothing about what it does and how it impacts bios reserving. If someone knows about this feature and how it might impact bios reserving, I would really like to know as well. Thanks.