Question Can I insert one 8gb ram instead of two 4gb rams in my pc Dell Inspiron 620s which has two slots and a limit of 8gb on motherboard.

Well ... actually Dell Inspiron 620s has Intel H61 chipset.
Compatible cpus with this chipset support up to 32GB of ram. Max config is 4x8GB.

With 2 ram slots it should be possible to use 2x8GB config.
So - technically it is possible. Dell just have not validated this config.
This may require BIOS update to work properly.
 
And where does this bios come from to maybe technically get it to work??

It is very common for oems to not conform to standards. They made it and say it has 8gb max, that's what it is then. They're not going to undo their own work because someone wants to go outside what they bought.

This answer is easy :)

You get 2x4gb at most
 
Dells from that era almost always supported more RAM than the maximum they claim, which is just the maximum they can be configured with from Dell.

With H61 the limitation is it only supports low density, so 8GB sticks max--provided those sticks each have 16 chips on them, or 4Mbit per chip. With only two slots, the max is therefore 16GB.

While Crucial only list a 2 x 4GB upgrade for that, two of their 8GB sticks work fine and other manufacturers offer 16GB kits.
 
Many years ago I fitted double the "maximum" amount of RAM specified by the manufacturer. The maximum capacity mentioned in the laptop user guide differed from the Kingston web site. The figure on the Kingston site turned out to be fully compatible.

I suspect that when the laptop manual was written, the largest SODIMMs available were 2GB. By the time 4GB memory became affordable, production of the laptop had ceased, so there was no incentive to update the manual for an obsolete product.

If your system isn't used for critical work and new RAM isn't too expensive, give it a go.
 
Is your particular version of the Inspiron 620 still on sale at the Dell web site?

If not and your computer has been replaced by a newer model, Dell probably regard your computer as obsolete.

As a result, they may not think it's profitable to spend time and money updating the manual/web site, if there's no chance of recouping the cost.

Check the Kingston and Corsair web sites for your computer model and see what upgrades they recommend. It's in Kingston and Corsair's interest to sell you the largest RAM kit possible, regardless of what Dell say. They

Just accept that some large manufacturers have a deliberate policy of not updating documentation for obsolete products. They're maximising their profits.
 
My graphics card (that is core i3 2120)has max limit of 32 gb and my motherboard(that is h61 chipset) has max limit 16 gb then why Dell suggests max ram as 8gb ??
The answer is obvious. Your CPU does indeed support 32GB of memory as does any other CPU that can fit into that motherboard. Dell chose to save a few pennies by choosing the H61 chipset which only supports up to four single-sided RAM or two double-sided, then only supplied two slots so two 8GB sticks for 16GB is the maximum given the low-density memory limitation. And further, they only chose to validate/qualify 8GB total for presumably marketing reasons as they did also offer better systems at the time, so it was a good way to steer the customer into spending more money, even though it really worked fine with 16GB.
All you have to do is throw away your Dell and get any H67 or Z68 retail aftermarket board with 4 slots and hey presto, your old CPU will work with four 8GB sticks for 32GB.
 
as i already stated, oem systems customize their parts. this is not a standard off the shelf motherboard nor is it likely to have a standard psu and so on.

what a cpu/chipset can support vs what an oem maker actually make it to support are 2 different things.

if you as wish to waste money buying 2 x 8gb of ram for a system that is not made for it, then that's your business. good luck to you

but coming here and suggesting to someone else to "give it a try, it theoretically should work" is not a good idea nor something that is acceptable.

2 x 4gb is what they designed it to do and all you should install. unless you are an expert in making custom BIOS and have the knowledge to prevent and deal with problems that arise, it is 100% not a good idea.

the answer to the OP is still a 100% no. 4 gb sticks is the largest you can use and 2 x 4gb is how you get the max 8gb of ram it supports.