The Cray Inc. XT4
| Machine type | Distributed-memory multi-vector processor |
|---|---|
| Models | XT4 |
| Operating system | UNICOS/lc, Cray's microkernel Unix |
| Connection structure | 3-D Torus |
| Compilers | Fortran 95, C, C++ |
| Vendors information Web page | www.cray.com/products/xt4/index.html/ |
| Year of introduction | 2006 |
System parameters
| Model | Cray XT4 |
|---|---|
| Clock cycle | 2.6 GHz |
| Theor. peak performance | |
| Per Processor | 10.4 Gflop/s |
| Per Cabinet | 998.4 Gflop/s |
| Max. Configuration | 319 Tflop/s |
| Memory | |
| Per Cabinet | ≤ 768 GB |
| Max. Configuration | 196 TB |
| No. of processors | |
| Per Cabinet | 96 |
| Max. Configuration | 30,508 |
| Communication bandwidth | |
| Point-to-point | ≤ 7.6 GB/s |
| Bisectional/cabinet | 667 GB/s |
Remarks
Architecturally the Cray XT4 is very much alike its predecessor, the Cray XT3, which is still marketed next to the XT4 (see the XT3). The main structure with respect to the internode network and the nodes themselves are still the same. However, there are some significant improvements compared to the XT3: the point-to-point network speed has doubled to a 7.6 GB/s bi-directional link and within the nodes dual-core Opterons at a clock frequency of 2.6 GHz are used, also doubling the peak performance per node. In addition, the memory bandwidth is doubled from 6.4 GB/s to 12.8 GB/s. However, the speed to the communication router, the SeaStar2 has stayed the same at 6.4 GB/s, the standard HyperTransport speed.
Measured Performances
As already given in the Performance section of the XT3, ORNL in the USA reports in [49] a speed of 101.4 Tflop/s out of 127.4 Tflop/s is reported on a 26,544 core system: an efficiency of 80%. ORNL in the USA reports in [49] a performance of 101.7 Tflop/s on a 23,016-processor regular XT3/XT4 system mixture for a linear system of size 2,220,160 with an efficiency of 85%. Furthermore, additional benchmark results for this system are available from Kuehn et. al., ([26]).