Originally posted by: Y-Master
Here are my questions:
1. Is the Opteron 856 compatible?
Yes, it should be. The 800 series are backwards with the 200 series but it would depend if the computer's BIOS recognizes the 856s or not.
2. What is the difference between the 856 and the 256?
The 256 has two HyperTransport (HT) links: one to the chipset (like any other 64-bit AMD CPU) and another to its neighboring CPU. The 856 has three links: one to the chipset, and two others to communicate with two neighboring CPUs. This third HT link allows for up to 8-way operation on the 856, while the two HT links limit the 256 to two-way operation. Additionally, the lack of a CPU-to-CPU HT link prevents an Athlon 64 or 1xx series or 12xx series Opteron from working in anything but a single-CPU setup.
3. Will there be a substantial difference in performance between the 256 and the 250?
The 250 is a 2.4 GHz chip and the 256/856 are 3.0 GHz chips. You should see something between a 20-25% increase in performance.
4. Is there any difference between the 250 and the 256 other than clock speed?
Not in your case. The 250 in your unit and 256 are both 90 nm single-core CPUs and are otherwise identical except for clock speed.
5. Why is it impossible to install dual core Italy processors in this socket 940 mobo? Is it a bios issue? Is there a hack that can make them work?
Theoretically they should work as machines that support 90 nm Opteron single-core CPUs should work with the dual-core CPUs as well. However, IBM may not have a BIOS update for the unit, which would prevent the Italy CPUs from working. Why don't they have an update? Who knows. They could just not want to be bothered or want you to upgrade to a newer model instead. You'd do better to get the IBM guys on the phone and ask them that question.
If it is just a BIOS issue, you could get the CPUs to work with a BIOS flash. If IBM does not make one that works, then you would have to modify the BIOS yourself. I have not modified a BIOS, but I hear it is possible but doing it wrong can corrupt the BIOS and require an expensive and out-of-warranty motherboard replacement.