Dimension 4700 4gb of ddr2 ram but only 3 usable on windows 7 64bit

The amount of usable memory will be something less than the 4GB in actual use.  More like 3 to 3.5GB depending on the system. Some even less than 3GB.  Is this what you are seeing?  

INTEL Graphics Steals 256 to 768 megs of ram and you never get this back.  Thats a limitation you cannot overcome.

Around 0.5GB (could be 1GB) is set aside for system operation.  System should detect 4GB and show 3-3.5GB as usable.  Or, is it detecting 3GB and showing something like 2.5GB as usable?

Its not just reserving for bios.  At least 256 megs is stolen for INTEL Graphics. Thats on top of the Ram Reserved for BIOS SHADOW. You never EVER get 4.0 gigs useable.  They improved this a tiny bit with the GX620 tower giving you 3.5 gigs total if you add 4 gigs.

You DO NOT get this back when you install a GPU.

• Chipset Type Intel 915G Express (Intel Graphics)
  
• https://www.intel.com/content/dam/support/us/en/documents/graphics/intel915g/sb/915gm910gmlexpresschipsetfamilydvmtpdf1.pdf

Thats why it says 4 gigs with 3.25 or less use able.

GX620 and Intel Pentium D 950/960  advantages

It has updated 945 graphics which means it supports windows 7 or 8 or 10.

https://www.walmart.com/ip/REFURBISHED-Optiplex-GX620-Tower-400GB-HDD-4GB-Ram-DVD-Rom-Windows-XP-Professional/803416719

The microprocessor includes Virtualization VT-X
that allows hyper-v virtualized programs.

I have seen inexpensive Pentium D's on Ebay and Amazon

SL9QQ seems to be the max for a 5150

Intel Cpu Pentium D 945 3.4Ghz Fsb800Mhz 2Mbx2 Lga775 Dual Core Tray

Intel - P-D 3.4GHz/4M/800 Dual Core CPU SL9QQ 

6 used from $12.00

its detecting all 4gbs of ram, and it has set aside 1gb for the bois it says

so it says 4.00gb (3.00gb usable)

yes but its taking a whole gb of ram and reserving it for bois

4.00 GB (3.00GB Usable)

**bleep**, and their is no way to get past it? thats really crummy.

well in that case is their another kind of motherboard that would fit in the dimension 4700 case and will work with the p4 670 and support all 4gbs of ram or more?

All do this.  If you had a motherboard that you could install more than 4GB of RAM then you would have more available.  But its a limitation of ALL motherboards (all brands of PC's) that have the 4GB RAM limitation.

You could gain a little bit more memory by using a 32 bit OS instead of 64 bit as the 32 bit does not use as much memory.

The 4700 is all proprietary.  Front panel connections are proprietary and undocumented.  Motherboard mounting holes are non-standard.  All Dell's are proprietary and even another Dell motherboard from a different model will have problems fitting and connecting to the front panel.  The rear motherboard I/O panel is built into the case, etc.  If you wanted to use a different motherboard, such as a standard ATX motherboard, you will also need an ATX case.  

ah ok, guess that is as far as i can take the old girl then

reason i ask is this was my "learing" pc, got it at a yard sale when i was 12 and learned alot about computers from tinkering with it, so i guess it holds a special place to me but im happy with what i was able to do with it now

thanks for the help every one 

why not move on.  end of year 2004, it has no value that old, sorry but none, see ebay completed auctions and learn.

buy uses PC 2012 or newer is best.

end the 4Gig limit . during the XP era (long gone)

the manual is clear as day.

"Your computer supports a maximum of 4 GB of memory when you use four 1-GB DIMMs"

this is not a limit, that is DELL invented all PCs cheap then were like that, 32bit XP cheap PCs.

there were in fact some XP64bit PCs then but are very rare... time to move on, for sure.

if the PC go goodwill and they seen it to IRAN... sorry

if cash is tight buy a used Dell 3020 and spend $50 no HDD and put in a SSD> 128GB for $20 used.

end the pain of relics.