A PCI Express graphics card.
Doesn't matter if the PCI Express graphics card uses the PCI Express 2.0 technology, or the PCI Express 2.1 technology.
The PCI Express graphics card, will insert into the PCI Express x16 expansion slot on the motherboard.
1) View of the motherboard in an illustration,http://h10025.www1.hp.com/ewfrf/wc/document?docname=c00378480&tmp_task=prodinfoCategory&lc=en&dlc=en&cc=us&lang=en&product=1127351
Scroll down the page to view the motherboard illustration.
A) Looking at the illustration, view the BATT. (CMOS Battery)
To the left of the CMOS Battery (BATT) are three white PCI slots.
Above them is a longer expansion slot. This is the PCI Express x16 slot.
Above it is marked > PCIX16X1 (PCI x16 times 1 slot)
NOTE* When installing the PCI Express graphics card, lift up gently on the Lock 'handle'.
It looks as though you should push down on it, but you need to lift up on it instead.
Also go above the motherboard illustration, and read to the right of the heading > Internal Connectors
In the list you will see > One PCI Express x16 graphics slot.
WHEN installing a graphics card, ALWAYS install the software from the CD disk provided, First!
Computer on, and Windows running, insert the graphics card's Installation disk, (CD) into the optical drive tray.
Install the software by following the directions.
THEN shut the computer down normally, and unplug the computer from power.
OBSERVE Anti-Static Precautions.
Install the graphics card.
Close the computer case, and plug the monitor into the graphics card.
Turn the computer on.
When you install a device (Such as a graphics card for example), Windows will try to find compatible drivers.
IF, THE driver is not installed First, Windows will match up one of it's thousands of generic drivers.
This = No.
You want THE driver installed first, so that Windows will find it, and Not try to match on of it's generic drivers.
It DOESN'T MATTER what graphics ram memory the graphics card has.
The graphics card's Processor and Ram Memory operates independent of the system resources.
The computer uses DDR Sdram ram memory.
The graphics card uses GDDR5 graphics ram memory.
It will work just fine.
It does NOT matter if your computer uses the PCI Express 1.1 technology, and the graphics card uses the PCI Express 2.0, or 2.1 technology.
PCI Express 2.0, and 2.1 technology is Backward Compatible with PCI Express 1.1 technology.
Will you get the full capability of the PCI Express 2.0, or 2.1 graphics card?
Will you notice?
What you need to look at it, is how much power will the graphics card use. Look at the system requirements for the graphics card, and be sure your Power Supply has enough power for that graphics card.
Also, IF, the graphics card requires additional power cables from the Power Supply, make sure your Power Supply has the required power cable, or power cables.
IF the Power Supply does not, use a power adapter cable.
Graphics card manufacturer's base the power needed for the graphics card, Not just on the graphics card itself, but on an entire computer system, AND the graphics card.
The graphics card manufacturers use a test computer system, that is a powerful computer system.
Gamer motherboard, Dual Core, or Quad Core processor, 4GB of ram memory, and at least two harddrives, and two optical drives, PLUS the graphics card in question.
This complete computer system uses a LOT more power than just the graphics card by itself.
There isn't a single graphics card out there, that uses more than 150 Watts by itself.
Recommendations for a graphics card that is compatible, with a Compaq Presario SR1620nx desktop computer?
Budget to medium:
Good enough to watch videos, older games, and some newer games.http://www.tigerdirect.com/applications/SearchTools/item-details.asp?EdpNo=4675217&CatId=3670
Higher level games, and large screen monitors,http://www.tigerdirect.com/applications/SearchTools/item-details.asp?EdpNo=6642574&CatId=3669
For questions post in a Comment.