On the side of my PC is written:
Acer Espire M3970
Windows 7 Home Premium 64-bit
Intel core i5 processor 2300
1 TB hard disk
Amd Radeon HD 6540 to 4095MB
8 GB Ram DDR3

But in my dxdiag is written:
Operating System: Windows 7 Home Premium 64-bit (6.1, Build 7601) Service Pack 1 (7601.win7sp1_gdr.110622-1506)
Language: Dutch (Regional Setting: Dutch)
System Manufacturer: Acer
System Model: Aspire M3970
BIOS: BIOS Date: 04/19/11 13:43:56 Ver: 04.06.04
Processor: Intel(R) Core(TM) i5-2300 CPU @ 2.80GHz (4 CPUs), ~2.8GHz
Memory: 8192MB RAM
Available OS Memory: 8174MB RAM
Page File: 2649MB used, 13697MB available
Windows Dir: C:\Windows
DirectX Version: DirectX 11
Card name: NVIDIA GeForce GT 440
Manufacturer: NVIDIA
Chip type: GeForce GT 440
DAC type: Integrated RAMDAC
Display Memory: 4063 MB
Dedicated Memory: 1503 MB
Shared Memory: 2559 MB
Current Mode: 1680 x 1050 (32 bit) (59Hz)
Monitor Name: Generic PnP Monitor
Monitor Model: JT229x1-1
Native Mode: 1680 x 1050(p) (59.954Hz)

So which one is true? And is that one better than the other one?

Go and get Belarc Advisor, this gives an accurate audit of your system.

Speccy is another nice free system info utility. The difference you may be seeing could be due to an onboard graphics (amd 6540) but the system had a card added (gt440). If you like free ware try FileHippo, they have both free and commercial trials and cover the gambit. You can find speccy and belarc there, just search them in its search window on the top right.

I would use CPU-Z from CPUID.com

As for your specs they are BOTH correct.
It is the Integrated Graphics that is being read, however.
Nvidia GeForce GT440 integrated graphics chipset,

GeForce 400 Series - Wikipedia, the free encyclopedia

Use a better program such as CPU-Z, or Belarc Adviser, (As already stated by Curleyben )

CPUID - System & hardware benchmark, monitoring, reporting

You can also check out the graphics specifications using GPU-Z,

GPU-Z Video card GPU Information Utility

As for which is better?
The dedicated graphics card, AMD HD6540 with 4GB's of graphics RAM.

Integrated Graphics uses some of the system's resources.
The Processor and RAM.
This slows the computer down, and the graphics process.

A dedicated graphics card has it's own Processor, (G.P.U.
Graphics Processing Unit), and graphics RAM.
It doesn't need, or needs VERY little, of the system resources.

A dedicated graphics card is always better than Integrated Graphics.

Regards,
joecoolvette

Re-read my previous post. Posting a more in-depth answer;

Processor: List of Intel Core i5 microprocessors - Wikipedia, the free encyclopedia

1024MegaBytes (1024MB) = 1GigaByte (1GB)
Your RAM amount (Memory:) is 8192MB, or 8GB. (1024MB x 8 = 8192MB)

A look at your motherboard not installed, and has no hardware components on it, (Not advertising for Ebay),

ACER ASPIRE M3910 DESKTOP MOTHERBOARD MB.SDX07.002 MBSDX07002 S1156 H57H-AM2 | eBay

Click on the photo of the motherboard to enlarge.

The alternate Blue and Black long slots, with the white Locking 'ears', are your RAM slots.

Right below the RAM slots is the processor socket. It is an LGA 1155 processor socket. (Socket has the contact pins, processor has the matching socket holes. There are one thousand, one hundred, fifty-five contact pins)

To the right of the processor socket is the PCI-Express x16 expansion slot. Black, with a white Locking Arm.

To the upper right of the PCI-Express x16 slot, (By the white Locking Arm), is the Southbridge chip. The Intel Core I processors do not use a Northbridge chip.
(QPI. Quick Point Interconnect ) (Nor do they use a FSB. Front Side Bus)

Processor has Solid Capacitors surrounding it. (Part of the Motherboard Voltage Regulator Circuit. They are probably Polymer solid capacitors. Regarded to be better than Electrolytic Capacitors)

Your computer IS using, (Provided you have your monitor plugged into the graphics card, and Not the motherboard), the AMD Radeon HD6450 graphics card.
(Should have caught that in the previous post. It is an HD6450, not 6540)

Northern Islands (GPU family) - Wikipedia, the free encyclopedia


Regards,
joecoolvette

DXdiag should be the correct one. Your system was set up with a either or video system. Yours seems to have the nvidia in it. Not ATI.

Acer Support: Specifications

Acer Support Specifications stated for Graphics:

"Intel® HD Graphics
Discrete card support for high-end NVIDIA® GeForce® and ATI Radeon™ graphic cards
Microsoft® DirectX® 11 support"

1) Intel HD graphics:

Means IF, the computer doesn't have a graphics card installed, it will be using one of Intel's series of HD Integrated graphics,

Intel HD Graphics - Wikipedia, the free encyclopedia


2) Discrete card support for high-end Nvidia GeForce graphics cards;

Means it can support high-end Nvidia GeForce series of graphics cards.

Comparison of Nvidia graphics processing units - Wikipedia, the free encyclopedia

2a) Discrete card support for high-end ATI Radeon graphics cards;

Means it can support high-end (HD) ATI Radeon graphics cards.

Comparison of AMD graphics processing units - Wikipedia, the free encyclopedia


The statements made in 2) and 2a) hold true, because;

A) The motherboard chipset that is used;

Intel H67 Express chipset,

List of Intel chipsets - Wikipedia, the free encyclopedia

An Intel Core I series compatible chipset.

Looking at the left column drop down to H67.
Now look across the chart, and under the heading - PCI Express Lanes.

PCI-Express 2.0 technology is used. (8 Lanes also )

Doesn't MATTER what GPU (Graphics Processing Unit) is used.

Nvidia GeForce series or AMD ATI Radeon series.

Regards,
joecoolvette