Upgrading system memory Win 7 64bit

I tried looking online about this I need to know if there's a big difference between 12GB of system memory and 16GB of system memory. I don't play many games but I do convert HD videos a lot and these programs are a pig on ram. I have 8GB now and have ordered 2 4GB sticks and was wondering if I should stay with 2 4GB sticks and 2 2GB sticks(total12GB) or should I upgrade to 16GB. And is there going to be any difference between 12GB and 16GB performance wise thanks for your help.

My pc works with DDR PC2-6400 RAM memory, is it possible to instal DDR3 PC3 15000 1866Mhz 240 Pin DIMM.
Thank you very much for the time spent with this issue.

Model Information
Model Name
a6643pt

Product Number
FZ096AA-AB9

Software Build
84PTv3PrA1

Serial Number
CZX8417F3Q
Operating System
Name
Microsoft Windows 7 Ultimate Edition (64-bit)
Service Pack
Service Pack 1
Build Number
7601
DirectX Version
11

System Information

Manufacturer
HP-Pavilion

Total Number of Logical CPUs
4

Total Physical Memory
4.00 GB

Total Number of Optical Drives
2

Total Number of Hard Drives
3

Total Number of Video Cards
1

Total Number of Memory Modules
4

Total Number of DIMM slots
4

Motherboard

System Board

Chipset
Intel G31/G33/G35/P31/P35

Southbridge
Intel 82801IR (ICH9R)


Base Board


Manufacturer
PEGATRON CORPORATION

Product
Benicia

BIOS


Vendor
American Megatrends Inc.

Release Date
09/10/2009

BIOS Version String
5.43

ROM Size
1.00 MB

Intel(R) Core(TM)2 Quad CPU Q8200 @ 2.33GHz

Name
Intel(R) Core(TM)2 Quad CPU Q8200 @ 2.33GHz

Cores
4

Threads
4

Current Speed
2.33 GHz

Multiplier
x 7.0 (6 - 7)

FSB Speed
1.33 GHz

Technology
45 nm

Features
MMX, PSE36, EM64T, SSE, SSE2, SSE3, SSSE3, SSE4.1, XD

L1 Instruction Cache
4 x 32.00 kB

L1 Data Cache
4 x 32.00 kB

L2 Cache
2 x 2.00 MB

Memory

Total Physical Memory
4.00 GB

1024 MB DDR2-SDRAM (PC2-6400 / 800 MHz)

Memory Size
1.00 GB

Memory Type
DDR2-SDRAM (PC2-6400 / 800 MHz)

Memory Manufacturer
Hynix Semiconductor (Hyundai Electronics)

Memory Manufacture Date
Week 34, Year 2008

Memory Part Number
HYMP112U64CP8-S6

Memory Serial Number
00002187

Memory Revision Code
4141

1024 MB DDR2-SDRAM (PC2-6400 / 800 MHz)

Memory Size
1.00 GB

Memory Type
DDR2-SDRAM (PC2-6400 / 800 MHz)

Memory Manufacturer
Hynix Semiconductor (Hyundai Electronics)

Memory Manufacture Date
Week 34, Year 2008

Memory Part Number
HYMP112U64CP8-S6

Memory Serial Number
00007127

Memory Revision Code
4141

1024 MB DDR2-SDRAM (PC2-6400 / 800 MHz)

Memory Size
1.00 GB

Memory Type
DDR2-SDRAM (PC2-6400 / 800 MHz)

Memory Manufacturer
Hynix Semiconductor (Hyundai Electronics)

Memory Manufacture Date
Week 34, Year 2008

Memory Part Number
HYMP112U64CP8-S6

Memory Serial Number
00001186

Memory Revision Code
4141

1024 MB DDR2-SDRAM (PC2-6400 / 800 MHz)

Memory Size
1.00 GB

Memory Type
DDR2-SDRAM (PC2-6400 / 800 MHz)

Memory Manufacturer
Kingston

Video Card

NVIDIA GeForce 9500 GS

Video Card Chip Type
GeForce 9500 GS

Video Card Memory
512.00 MB

Crucial's memory scanner will check your system and suggest the best RAM upgrade for you.

SDRAM, DDR2 and DDR RAM memory upgrades from Crucial.com

seavixen32 said:

Crucial's memory scanner will check your system and suggest the best RAM upgrade for you.

SDRAM, DDR2 and DDR RAM memory upgrades from Crucial.com

Thanks you.
I did it but for some reason it does not answer my question.

joaquim said:

seavixen32 said:

Crucial's memory scanner will check your system and suggest the best RAM upgrade for you.

SDRAM, DDR2 and DDR RAM memory upgrades from Crucial.com

Thanks you.
I did it but for some reason it does not answer my question.

You should have started a new thread, rather than appending a question onto anothers.

Your specs:

HP Pavilion a6643pt Desktop PC Product Specifications HP Pavilion a6643pt Desktop PC - HP Customer Care (United States - English)

Short answer: DDR2 only. (DDR2 and DDR3 are the same size, but they use different notches. One will not fit in the other type's slot.)

Here's what Crucial recommends for your system:

Computer memory upgrades for HP - Compaq Pavilion a6643it Desktop/PC from Crucial.com

(This is for the Italian model. I doubt that things are different for Portugal.) If you aren't in the US, Canada, or the UK, you may bneed to find a different source.

The largest individual DIMMs officially supported for your PC are 2GB, so that maximum memory possible is 8GB (4 X 2).

I am sorry for my mistake and thank you very much for your help.
Joaquim