Can old oem sata hard drive be replaced with a new current generation sata III hdd on an 8 year old xps 8100 with an i7 chip??

Any 3.5" SATA drive will work.

As long as the system is in working order, and you purchase a SATA data cable for the additional drive, you should have no trouble cloning the existing drive to a new one.

I recommend

https://www.amazon.com/Blue-Cache-Desktop-Drive-WD10EZEX/dp/B0088PUEPK/

Advanced Format Drives (Drives made after 2011 and larger than 120gig) Require F6 drivers and windows 7 SP1.  The good news is that you can now download a windows 10 ISO and activate with your windows 7 COA key.  The F6 drivers are still required because newer and newer versions of the INTEL RST do not support older chipsets from 2006 thru 2010  aka ICH6 ICH7 ICH8 ICH9 ICH10.

The INTEL RST 9.6  F6 Drivers are required for windows 7, 8 and 10 can be put on a USB Flash drive and when AHCI is enabled for Sata operation it will load the drivers and see the disk.  If you do not load RST 9.6 or higher it will not "see the drive" and will not install.  Advanced format 4k drives started arriving in 2011.  At this point ALL NEW Drives are advanced format.  If you have an ancient 120 gig , 80 gig drive it won't need the drivers.   Most 160 Gig, 320 gig , 500 gig etc are 4k Advanced format Drives.

https://downloadcenter.intel.com/download/15251

How to install and activate Windows 10 using your Windows 7 or Windows 8 product key

Please note: The copy of Windows 10 you download must correspond with the edition of Windows you are licensed for:

• Windows 7 Starter, Home Basic, Home Premium, Windows 8.0 Core, Windows 8.1 Core must use a Windows 10 Home ISO
• Windows 7 Professional, Windows 7 Ultimate, Windows 8.0 Pro, Windows 8.1 Pro must use a Windows 10 Pro ISO
  
• If you are using Windows 7 Enterprise, Windows 8.0 Enterprise, Windows 8.1 Enterprise editions you won't be able to use the free upgrade offer.

Review complete instructions how to download the Windows 10 ISO in the following article:

How to download official Windows 10 ISO files

Review instructions here how to start a clean install if you desire, if you want to perform an upgrade, click here.

Have your Windows 7 or 8/8.1 product key ready. If you purchased a retail license, you can find the product key within the product box. The Windows 7 product key is normally found on an orange sticker attached to a pamphlet inside the box. The Windows 8/8.1 product key is found on a small business size card. See examples below. Please note, you can also use your OEM product key too if Windows came preinstalled on your computer.

If Advanced Format drives are an issue here is a list from Western Digital that lists drives that are and are not Advanced Format - products.wdc.com/.../2178-001010.pdf

With a 9 year old Dell I would question whether or not Windows 10 is a good choice. There are probably some who have been successful installing Windows 10, but the XPS 8100 is not on Dell's list of those tested for Windows 10. You will not find hardware drivers for the XPS 8100 on the Dell support site if support is not already built into Windows.

There is no reference to Advanced Format drives in these articles about the need for F6 drivers for Windows 7 for drives under 2 TB - www.intel.com/.../000005611.html and www.dell.com/.../intel-rapid-storage-f6-drivers-for-windows-7-and-windows-8-81

I see no reason you cannot restore your data using Macrium Reflect. Too bad you didn't image the whole disk then you would not have to re-install Windows.

https://www.walmart.com/ip/55080037

Home windows is $109 and Pro Windows is $199

Retail its $119 and $249

https://www.walmart.com/ip/799896321

GX620 Tower.

Bios Updated to A11,  4 Gigs of Ram installed still Registers 3.50

Pentium D 820 was Replaced with Pentium D 915.  DELL HH807 Motherboard Bios A11.  Copper Heatsink  305W Tower.

I added a Radeon 6670 Video card.  All drivers are native to windows clean install.  I added directshow legacy feature and installed directx june 2010.  After windows updates everything works as expected.

There are ZERO issues with older Dell models including those that go back to 2006 like the optiplex GX620 and newer.  This is why you can update the bios to A11 and install msdos all the way to windows 10 pro.  Not being on the supported list just means that you wont get help from microsoft or Dell with windows 10.  It DOES NOT MEAN that there are ANY issues with running windows 10 on these systems.

http://www.pcliquidations.com/p9780-dell-optiplex-gx620-tower

This is what Dell said 5 years ago

"Officially no, Dell has not listed this system for Windows Vista or Windows 7 compatibility and as such no drivers are officially available directly on the drivers and downloads page." (Acutally the Vista Drivers were listed but this has become broken)

How does Windows Vista run on legacy systems - Dell OptiPlexTM  GX260s, GX270s, GX280s and GX620s? Will Windows Vista operate on these if the systems are upgraded to 1-2GB of RAM?

There ARE Vista Drivers.  No Windows 7 Drivers from Dell.  (Dell Officially Listed this system as Designed for Windows XP/Vista Capable)

You will be Much Happier with the Upgrade Result if you Get 4 Gigs of Ram and a RADEON 6450 minimum.

48 new from $39.93

It is up to idreos what he wished to do, but in my opinion I don't think it is prudent to recommend to someone with an 9 year old system with a bad HDD and familiarity with Windows 7 to learn a whole new OS just to fix his HDD.

Windows 10 works fine on most dells from 2006 on.  Saying any different is FUD.Fear, uncertainty, and doubt (FUD) marketing trying to get people to buy new.  GX620 and up Optiplex are fine.  Same with Dimension systems.   Since microsoft does more and more to force windows 10 its prudent to help people along to an os that will be supported past 2020 with 2017 almost gone.

https://www.walmart.com/ip/55099006

The original poster seems happy with Windows 7 and the OS works fine on his computer. No one is trying to get him to buy a new computer because of a failed HDD. While Windows 10 may work on his computer there is no guarantee certainly not from Dell or Microsoft. In the 9 years he has owned this computer he may have added a device, i.e. printer, that doesn't work with Windows 10. Windows 10 is not the solution in this case which is replacing a failed HDD.

Windows 10 is a solution and works fine.