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You are here: Compendium » Hardware » HardwareAltix

HPC Component SGI Altix

The SGI Altix 4700 is a shared memory system with dual core Intel Itanium 2 CPUs (Montecito) operated by the Linux operating system SuSE SLES 10 with a 2.6 kernel. Currently, the following Altix partitions are installed at ZIH:

Name Total Cores Compute Cores Memory per Core
Mars 384 348 1 GB
Jupiter 512 506 4 GB
Saturn 512 506 4 GB
Uranus 512 506 4 GB
Neptun 128 128 1 GB

The jobs for these partitions (except Neptun) are scheduled by the PlatformLSF batch system running on The actual placement of a submitted job may depend on factors like memory size, number of processors, time limit.


All partitions share the same CXFS filesystems /work and /fastfs. ... more information

ccNuma Architecture

The SGI Altix has a ccNUMA architecture, which stands for Cache Coherent Non-Uniform Memory Access. It can be considered as a SM-MIMD (shared memory - multiple instruction multiple data) machine. The SGI ccNuma system has the following properties:

  • Memory is physically distributed but logically shared
  • Memory is kept coherent automatically by hardware.
  • Coherent memory: memory is always valid (caches hold copies)
  • Granularity is L3 cacheline (128 B)
  • Bandwidth of NumaLink4 is 6.4 GB/s

The ccNuma is a compromise between a distributed memory system and a flat symmetric multi processing machine (SMP). Altough the memory is shared, the access properties are not the same.

Compute Module

The basic compute module of an Altix system is shown below.
Altix compute blade

It consists of one dual core Intel Itanium 2 "Montecito" processor, the local memory of 4 GB (2 GB on Mars), and the communication component, the so-called SHUB. All resources are shared by both cores. They have a common front side bus, so that accumulated memory bandwidth for both is not higher than for just one core.

The SHUB connects local and remote ressources. Via the SHUB and NUMAlink all CPUs can access remote memory in the whole system. Naturally, the fastest access provides local memory. There are some hints and commands that may help you to get optimal memory allocation and process placement ). Four of these blades are grouped together with a NUMA router in a compute brick. All bricks are connected with NUMAlink4 in a "fat-tree"-topology.
Remote memory access via SHUBs and NUMAlink


The current SGI Altix is based on the dual core Intel Itanium 2 processor (codename "Montecito"). One core has the following basic properties:

clock rate 1.6 GHz
integer units 6
floating point units (multiply-add) 2
peak performance 6.4 GFLOPS
L1 cache 2 x 16 kB, 1 clock latency
L2 cache 256 kB, 5 clock latency
L3 cache 9 MB, 12 clock latency
front side bus 128 bit x 200 MHz

The theoretical peak performance of all Altix partitions is hence about 13.1 TFLOPS.

The processor has hardware support for efficient software pipelining. For many scientific applications it provides a high sustained performance exceeding the performance of RISC CPUs with similar peak performance. On the down side is the fact that the compiler has to explicitely discover and exploit the parallelism in the application.