I received a PM regarding the xw6400, and wanted to share the answer. I am amazed that these xw6400 workstations are still going strong, including running with W10Pro64. The very highest end processor that HP ever certified for this workstation is so very reasonable on eBay.... Here is his question:
"I write you to ask if you know something about the problem I occured. I try to change my old CPU Xeon x5160 with a Xeon x5470, but after installing fan is power on but no boot or bios interface just black screen. Motherboard is HP FMB-0601.
Best regards,
Raul"
Answer: Raul, I am happy to help, and that is still an excellent workstation well worth upgrading at a low cost. You may know that there are two versions of the Z600 and the Z620, and it is similar with the xw6400. There are two kinds of these, but not officially. There is one kind that will run one or two of the very fastest quad core processor that HP ever certified for it.... the E5345. If the workstation can run one it can run two of those.
The Intel processors such as the E5345 may have several versions, and the latest is always what you want. You can find that by knowing the latest "sSpec" code from Intel. Search that one out on eBay by looking for SLAEJ, and only buy that one. There are two other earlier versions of the E5345. The socket for the xw6400 is the LGA771/PLGA771.... same thing. P means plastic.
Regarding the X5470 it uses the same socket, but was never certified for the xw6400. In fact it was never certified for the xw8400 or the xw6600. It fits in the same type socket but it is from a different family of processors and was only certified for use in the xw8600. Nice try, but the max you can do with your xw6400 is the E5345 SLAEJ processor, two of them.
Now, back to the beginning..... there are about 10% of all xw6400 that simply cannot run one or two E5345 processors. You'll really not know until you try. So, I recommend buying one of those off eBay (about $7.00 USD today). Get two if one works. Use two of the E5160 processors if the E5345 processors will not workin your particular xw6400.
Next steps up: xw6600 with two of the fastest quad cores certified by HP. Then the Z400 version 2 with a single hexacore X5690. Then two of the fastest HP certified quad core or hexacores HP certified for the version 2 Z600. I'm still running some of the xw6400s to show my partners what still can be done with them, and all the rest up to the Z640 workstations. Got to give HP credit......
Best, Scott