?? First dell desktop that will recognize 3 tb hard drive

The 8400 should recognize 3tb drives, but only under Vista or Windows 7 and not for boot purposes.

3TB drives Requires 64 bit CPU, BIOS, OS.  AND GUID Boot Code with the latest INTEL Rapid Storage Drivers or 3rd party Card that does EPT Booting.  32 bit generic boot code in the MBR cannot support 3TB.

GPT allows for a maximum disk and partition size of 9.4 zettabytes.Most current operating systems support GPT, although some operating systems (including Mac OS X and Windows) only support booting from GPT partitions on systems with EFI hardware aka the "BIOS" to boot can be in an addon Controller.

The MBR BIOS partition table restricts partition sizes to a maximum of 2.19 terabytes or almost exactly 2 TiB (2,199,023,255,040 bytes or 4,294,967,295 (232−1) sectors × 512 (29) bytes per sector).

Western Digital Does this with a GX620 and a PCI-E Card with Boot Rom.

Since most current systems don't yet support UEFI standards, WD is providing an interim solution for those who want to boot these high-capacity drives in certain operating environments; they're including an AHCI-compliant  host bus adapter (HBA) card with the retail drive kits. This allows legacy BIOS motherboards and GPT-ready operating systems to use a known driver to correctly support large capacity drives. While not a perfect solution, WD had to either go this route or hold off until UEFI adoption warranted the drive release.

The rules are slightly different when using the drive in a non-boot scenario, simply as a secondary storage device. Here the drives play well with 32-bit operating systems when used with or without the included HBA (depending on OS). The following chart breaks down the scenarios:

1. Presently WD does not directly provide support for these applications. We have worked extensively with our partners and solutions may be available. HBA and RAID Controller vendors may have developed solutions for these applications.
2. Linux solutions are available. Please consult your Operating System provider for use with Large Capacity drives.
3. An available PCI-E slot for the HBA is required. Supported by using the native Windows Advanced Host Controller Interface (AHCI) drivers only.
4. Apple Bootcamp is presently not supported. Support is limited to the operating system only.
5. Boot support requires a system with UEFI Support and a 64 bit version of the OS.
6. Check with USB Bridge provider to verify if and how Large Drives are supported.

My 3tb hard drive is a Hitachi, and it worked in my 2350 (which does not have onboard SATA support) with the aid of a five-year-old Rosewill RC-210 eSATA/SATA card. I also verified that a seven-year-old Syba 150R SATA card would work with the same drive. A machine with onboard SATA should not need a SATA card.