In the following guide, I will explain what the numbers mean in a Video Card and how to choose a balanced Card. there are two video card chipset makers out there: Nvidia and ATI (ATI is now AMD).The Nvidia Geforce series began with series 1 till the GT 500s.

The Ati Radeon starts with R7000 till the HD7000

DX9 cards: Nvidia Geforce 5 -> Geforce 7, ATI Radeon 9500 -> Radeon X1900

DX10 Cards: Nvidia Geforce 8 -> Geforce 300, ATI Radeon HD 2000 -> HD 4000

DX11 Cards: Nvidia Geforce 400 -> 500, ATI (AMD) Radeon 5000 -> 7000

At this guide we will look at the Nvidia cards, please note that the same concept applies to the ATI (AMD) cards

let's take the Geforce 9 series and the Geforce 8 series (same concept but applies for older cards)
The Geforce 9 series begins with the Geforce 9100 and ends with the Geforce 9800.
The Geforce 9100 till the Geforce 9300 are only built in the motherboard (could find some exceptions)
and the Geforce 9400 till the 9800 series come as PCi express cards (some exceptions apply).
The Geforce 8 series starts with the Geforce 8400 and ends with the Geforce 8800 series.
But what do these numbers really mean?
In Video Cards, always look at the second number, then look at the first number

please not that you cannot ignore the first number, but it's just that you have to follow that hierarchy.

eg: in Geforce 9 600 and Geforce 9 800
800 is bigger than 600
9 = 9

so 9800 is faster than 9600

Now let's take another example with two cards from different series:

Geforce 8 600 and Geforce 9 600
600 = 600
9 > 8
so that means Geforce 9600 is better than Geforce 8600.
Now what about a Geforce 8800 GT and Geforce 9600 GT?
As I said above, please look at the second number (in this case 800 and 600 respectively)
800 > 600
but: 8 < 9
does that makes the 9600 better than the 8800?
No! It's a bit close to it but not faster; the 8800 is still better.

After the launch of the 3 numbers Nvidia Cards, people are more confused; are they better than the 8 and 9 series?

Nvidia is just continuing the series naming so after the 9 series, there is 100 series
, 200, 300, 400, 500.

Let's start with:
Geforce 100 series. This starts with the Geforce 100 and ends with the Geforce 150. Note that these cards only come with pre-built PCs and can't be bought as a retail.

Geforce 200 series: 205 -> 295 (all cards before Geforce 220 come integrated in the Nvidia motherboard)
So as with the old Geforce naming, the same concept applies here:
Low End Cards: 205 -> GT 240
Mid Range Cards: GTS 240 -> GTS 250
High end cards: GTX 260 -> GTX 295
Note that:
- GTS 250 = Geforce 9800 GTX+ but with a better technology, but are called Mid Ranged cards because the 200 series are more powerful now
- GTS 240 (and not GT 240) = (and slightly better) than Geforce 9600 GT
- everything above GTS 250 is better than the 9 and 8 series.

DX11 Cards:
Geforce 400 Series: GT 420 -> GTX 480
Low End: GT 420 -> GT 440
Mid Range: GTS 450
High end: GTX 460 -> GTX 480

Geforce 500 Series: GT 520 -> GTX 590
Low End: GT 520 -> GT545
Mid Range: GTX 550 Ti
High End: GTX 560 -> GTX 590

Let's continue the comparison in the new Nvidia series:

Geforce GTS 250 and Geforce GTS 450

50 = 50
4 >2
Please note here that the GTS 250 is DX10 (DDR3) but the GTS 450 is DX11 (DDR5)
GTS 250 has 256 bit DDR3
GTS 450 has 128 bit DDR5
The GTS 450 is still better because it has the DDR5 DRam Type, so it has much more memory interface, but because of its 128 bit interface it's not much of a performer in Directx 11 games, but when it comes to DX10 and DX9 the GTS 450 is better than the GTS 250

Geforce GTX 260 and Geforce GTX 550 Ti

60 > 50
5 > 2
The GTX 260 is a DX10 card and is a high end card in the GT 200 series.
It has DDR3 Dram Type, and an amazing 448 Bit bus width.
The GTX 550 Ti is a DX11 card and it is a mid Range card in the GT 500 series. It has DDR5 Dram Type, and 192 Bit bus width.
Now we saw that the 60 in GTX 260 is bigger than 50 in GTX 550 Ti
But still the DDR5 in GTX 550 Ti plays an amazing role in performance especially in DX9 and DX10 games, and it can perform better than the GTX 260. When it comes to DX11, it can play the latest DX11 games on Mid high settings depending on the resolution.

Please note that :

- Video Memory is not everything in a Video Card, it's the last thing you should look at
- The Graphics Memory technology DDR (Double Data Rate) is very important to identify the Video Card performance and can vary from DDR1 (slowest) to DDR5 (Fastest)
- the DDR can define the memory interface of the Video Card, (32 bit up to 512 bit)
DDR: 32 to 64,
DDR2: 64 to 128,
DDR3 to DDR5: 128 to 512 bit (some cards will have a 2x bit, eg: (2×384)
- Core Clock and memory Clock is important as well
- a High end card from the 9 series like the 9800 GT won't stay high end
forever you know.
- The new Nvidia and ATI(AMD) Cards will needs two slots, but that does not mean that it needs two PCIex slots, but it will take the physical place of two cards (Refer to the GTX 550 Ti Picture), so you have to have two empty slots to be able to install the card in your motherboard.
- a PCIex 2.0 card (Geforce 9 series and above) does not necessarily need a motherboard with a PCIex 2.0 slot, a PCIex 1.0 slot is compatible with it.
- a High End video card (any series that has a high 2nd number >= 6, (eg: 9800 GT, GTX 260, GTX 560, GTX 460, GTX 580, etc… are power hungry cards, meaning it needs a good quality Power Supply Unit (PSU) withat least650 W and 32 Amps under the +12V rail. To find out if a PSU is a good quality, it must have the "80 Plus Certified" logo.
- The symbols that come after the card (GT, GS, GTS, GX, GTX, etc..) also defines the card's performance (for more information please go here:Nvidia GeForce,ATI Radeon