X-bit labs

Server Platforms Today

Category: CPU

by Victor Kartunov

[ 04/29/2004 | 04:49 PM ]

In this theoretical article we are going to take a closer look at the multi-processor architectures used in contemporary servers and will dwell on a few server processor, which are not that well-known to the public yet. Namely, we are going to reveal all secrets of the Intel Itanium and Hewlett Packard PA8700, as well as Alpha, MIPS, SUN UltraSPARC and of course IBM Power4 microprocessors.

Table of contents:

• Processor Performance
  
• System Bus
  
• Types of Multiprocessor Architectures
  
• Cache Memory
  
• Cache Coherency
  
• Modern Server Processors
  
• Intel Itanium Platform
  
• Architecture of Itanium-Based Systems
  
• Itanium Micro-Architecture
  
• The Itanium in Perspective
  
• Hewlett Packard PA8700
  
• Alpha Microprocessor
  
• MIPS Microprocessors
  
• SUN UltraSPARC
  
• IBM Power4
  
• Conclusion
  

Traditionally, we classify processors in three vast leagues: for the home PC, the mainstream and for server systems. Today I’m going to talk about the latter category.

What is a server processor? Taking the meaning of the term literally, we have that it is a processor that works in a server. Or serves in a server if you like. Anyway, this chip often determines the consumer qualities of a server computer. First of all, the server, however overwhelmed with work it is, must quickly respond to users’ requests. It must be fast at performing the tasks the owner of the server has set for it. Thus, the processor performance and of course reliability become the most important factors for choosing the appropriate server platforms. In other words, servers are speed plus reliability. Cost is a secondary matter, although an important factor too (money is always important).

Besides performance, which I will discuss shortly, other characteristics determine the value of a processor for integrators of server systems. I think the most important factors are:

• Reliability;
• Performance;
• Scalability;
• Software architecture (i.e. the instruction set of the processor and the spread and popularity of software for this platform);
• Cost;
• Heat dissipation;
• Availability.

We will see below what the performance of a server processor depends upon. Right now, let me add a few words on each of the items of the list.

Reliability is of the highest priority for server manufacturing, since the server usually has to deal with very valuable data. Frankly speaking, the properties of the processor don’t usually tell on the overall reliability of the system as hard disk drives and fans are much more likely to fail. In other words, if we don’t count in possible errors during CPU manufacture (like the notorious coprocessor error in the Pentium), the reliability of nearly all modern processors is more than enough for today. If you follow the usage rules, of course …

Scalability means the readiness of the platform to performance growth, both for the single processor and for their number in the system. Of course, processors themselves and the technical properties of the platform will limit the growth opportunities – starting from some CPU frequency (and from a certain number of processors per system), the performance won’t practically change. The level of this saturation depends on too many parameters and I will discuss this problem below, too.