AMD 760MP & Athlon MP - Dual Processor Heavenby Anand Lal Shimpi on June 5, 2001 12:00 PM EST
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Memory: 1GB is barely enough
Here's something to try with your overclocked desktop boards: fill all of your memory banks and run a constant barrage of CPU/memory intensive tests on your system. If your system can stand this sort of torture then you've truly got a solid desktop machine, but chances are that it wouldn't be able to handle this load for months on end without a single reboot. This is the type of stress a mission critical server must deal with.
It is rare that you see a high-end server outfitted with less than 1GB of memory. This is one of the reasons that RDRAM has been kept out of the server market because when you're dealing with multiple gigabytes of memory, a more expensive memory technology can easily raise server cost by thousands of dollars. This is also the reason that Iwill's i860 motherboard that we previewed two weeks ago has 8 memory slots - to allow for up to 4GB of RDRAM to be installed. Even at AnandTech, our Forums Database server is outfitted with 1.5GB of SDRAM and it doesn't handle nearly as much traffic as the database servers at websites such as Yahoo and CNet. You can only imagine the type of memory configurations they have running over there.
Adding more memory can easily improve performance by hundreds of percentage points in database serving applications depending on load. In the workstation arena, when modeling extremely complex designs, it isn't rare to see systems outfitted with 16GB of memory. Remember that one of the reasons Intel designed the 64-bit Itanium processor was so that they could use it to design their next-generation microarchitecture. One of the biggest benefits of 64-bit processors is their ability to address beyond 4GB of memory, a limitation of 32-bit processors (2^32 bytes). This means that 64-bit microprocessors will be able to address more than 18,446,744,073GB of memory. Although that is quite a bit, remember that it was once thought that nobody would ever need more than 640K of memory. To put it simply, there is a need for massive amounts of memory in these types of systems, much more than what you'd use in your desktop computer.
Reliability is not second to memory size; it is easily an equal when it comes to workstations and servers. This is why ECC memory is often a requirement in the high-end environment. In many cases, in order to allow for higher density modules, registered memory is required as well. This is the case with the Tyan 760MP motherboard we are taking a look at today that does, in fact, require the use of Registered DDR SDRAM.
For those of you not familiar with Registered DIMMs, they are generally not the same type of modules you use in your personal systems except for a few unusual cases (you will most likely know if you have registered memory or not). In contrast to unbuffered SDRAM (conventional SDRAM), Registered SDRAM features small registers present between the module's interface and the actual SDRAM chips on the PCB. They are often used to decrease loading and allow for more physical SDRAM devices to be used on a single DIMM.
Bandwidth actually matters
AMD, Intel and VIA have all been guilty of promoting higher bandwidth memory technologies on the desktop platform, but the performance improvement over previous "low bandwidth" technologies is relatively small. The reason behind this is that most of today's applications aren't bandwidth intensive enough to take advantage of this additional bandwidth that they've been given. It's like having a four-lane highway but only three cars to take advantage of it. However, it is best to plan ahead and add the fourth lane instead of getting caught with your pants down by only having three lanes when there are more cars present later.
With workstations and servers, the applications already take advantage of the bandwidth that these new memory technologies offer. This is partially why the single processor Athlon on an AMD 760 motherboard did so well in our recent database server tests, compared to the dual processor Pentium III.
As more processors are added to the equation, the need for more memory bandwidth increases as there are now multiple CPUs competing for the same memory bandwidth. This is why the ServerWorks Grand Champion HE with support for up to four Intel Xeon processors is outfitted with 6.4GB/s of memory bandwidth courtesy of its quad channel DDR200 memory bus.
Bandwidth to the CPUs also matters, which is determined by the speed and bus width of the FSB. That's another reason why a single Athlon, with its 266MHz EV6 bus, did so well in many of our recent server tests.
With these requirements in mind, we can now take a look at the architecture behind the Athlon MP processor and the 760MP chipset.