Aurora R13, installing extra HDD

The storage specs for your R13 are as follows:

Your Alienware Aurora R13 supports one of the following storage configurations:
● Up to two M.2 2230 or M.2 2280 PCIe NVMe solid-state drives
● Up to two M.2 2230 or M.2 2280 PCIe NVMe solid-state drives + one 3.5-inch hard drive or 2.5-inch hard drive
● Up to two M.2 2230 or M.2 2280 PCIe NVMe solid-state drives + one 3.5-inch hard drive + one 2.5-inch hard drive
NOTE: Your Alienware Aurora R13 comes shipped with one 3.5-inch hard drive. When installing an additional 2.5-inch hard
drive, contact Dell.com technical support to purchase an additional SATA cable to connect the 2.5-inch drive to the system
board.
The primary drive of your Alienware Aurora R13 varies with the storage configuration. For computers:
● With a M.2 drive, the M.2 drive is the primary drive.
● With a M.2 drive and one 3.5-inch hard drive, the M.2 drive is the primary drive

So to answer your question, yes you can add a 4TB Gen 3 M.2 NVMe/PCIe SSD.

With such a nice computer, booting and running Windows and Apps from a (slow) spinning-platter HDD is a bit of a travesty. 

A 2.5 SATA-SSD is about 4 times faster. A NVMe-SSD (M.2-PCIe as you call it) are about 5-8 times faster than a SATA-based one.

Re: Can I install another HDD and open my Alienware without breaking my warranty?

no you would not void warranty if you open pc and install your own ssd or hdd.  it is better you wear ESD wrist band to prevent static.  If you are new to pc and your Windows OS was installed on a single 2TB hdd, and you are comfortable with the boot drive hdd speed, it might be easier for you to add a second 2.5” 4TB ssd or hdd.

Your Alienware Aurora R13 comes shipped with one 3.5-inch hard drive. When installing an additional 2.5-inch hard drive, contact Dell.com technical support to purchase an additional SATA cable to connect the 2.5-inch drive to the system board.

Nothing much to add to suggestions/answers below apart from the fact what your 12th gen Intel CPU PC with Z690 chipset also supports Gen4 NVMe drives in M.2 slots (but if adapter is used in one of two x4 PCIe slots then Gen3 standard would be max, not sure why Dell has done it this way since PCH has support for up to x12 Gen4 lanes - therefore should be sufficient even if we account for secondary M.2 slot taking another x4 lanes, unless they've also used x2 lanes for WiFi M.2 slot from the same basket {in non-CNVio/CNVio2 scenarios}). One x16 PCIe slot (CPU-bound) is actually Gen5 (but it's dedicated to GPU).

This information just points out what NVMe Gen4 drive would be a better option since it's almost twice faster vs Gen3

If you a Admin or  Moderator from Activeworlds, no. For other brands, no. Worldspace is what you buy or wat you create, youi dont need a extra hdd because  the 3D world you purchased  or manage is controlling that. You don't need a extra HDD for that.

And Unreal is gone....what are you building, bro?

Why would you want to put a hard drive in a R13? Even the base model should not have one. It has 2 x SSD slots, fill those and away you go. Guarantee you the vast majority who bought the high end Intel versions of the R13 opened the box and ditched a brand new hard drive in favour of a second SSD. I do not understand why Dell even supplied a hard drive. 

HDDs are of magnitude better vs SSDs in terms of $ per GB,
getting 8TB NVMe SSD from reliable supplier will cost above $1K
while 3x more capacity of say 22GB HDD (e.g. archiving, backups) will cost only half of it.
Spreading files across multiple storage devices (we're not talking about servers) in an attempt to get more performance for most home scenarios doesn't make much of sense 

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@sam55todd wrote:

HDDs are of magnitude better vs SSDs in terms of $ per GB,
getting 8TB NVMe SSD from reliable supplier will cost above $1K
while 3x more capacity of say 22GB HDD (e.g. archiving, backups) will cost only half of it.
Spreading files across multiple storage devices (we're not talking about servers) in an attempt to get more performance for most home scenarios doesn't make much of sense 

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Right. But, 

a. Why make your main bootable C-Drive (that holds/runs Windows and main-Apps) a spinning-platter HDD ?

b. Who needs that much storage INSIDE a desktop? I still use (large capacity) spinning-HDDs but only for archive storage and backup (in Synology-NAS and portable external enclosures).

For response to section b. : Simply because Windows don't like you running everything on the C- drive, thatswhy you need a spinning HDD for install programs or games. 

As a '' Registered .... Partner and Apple Developer'' you should know that.

You can use an SSD or NVMe drive as a second drive. I would do that over a spinning drive, especially in a higher end system.

At the same time there's nothing wrong with using your C drive for programs or games. Especially if it's the only NVMe drive in your system. It will be faster than using a SATA SSD or traditional platter drive.

If you require more than 8 GB of storage capacity I would recommend a NAS solution over a local attached drive, for the extra benefits it can provide.