XC40 Machine Overview

Theta is a Cray XC40 and consists of several types of nodes. Table 1 summarizes the system’s capabilities.

Table 1

Theta Description Aggregate
Compute Nodes Intel KNL 7230 4,392
Compute Cores 64 281,088
Compute Memory - DDR4 192 GB 843,264 GB
Compute Memory - MCDRAM 16 GB 70,272 GB
Compute SSD 128 GB 562,176 GB
LNET Service node for Lustre 30
DVS Service node for Cray DVS 60
Compute Racks   24
LINPACK RMax (Rpeak) Top500 LINPACK results 6,920 TFLOP/s
(11,693 TFLOP/s)
Tier 2 Service Node 13
MOM Service Node 3
eLogin Login node 6
Project File system Lustre 10 PB
Home file system GPFS 1 PB
High Speed Network Aries Dragonfly 14400 rank 1 ports
14400 rank 2 ports
9600 rank 3 ports


Login Nodes

Theta has six login nodes that are Cray eLogin machines, which means they are nodes outside the main Cray system. These nodes are Intel Haswell E5-2698 v3 nodes with 256GB of DDR4 memory. These frontend nodes are used for editing code, building code, and submitting jobs. All users of the Theta system share these nodes. Please note that these nodes are not 100% binary compatible with AVX-512 instructions so applications compiled for the compute node will not run on the login nodes.

Service Nodes

Service nodes are Cray’s generic name for various nodes that provide internal infrastructure for the overall system. These nodes appear in the xtnodestat output as service nodes and consume part of the Node Identifier (NID) space. This is important with respect to job scheduling because requesting a NID that is a service node will cause your job not to run.


The Machine Oriented Mini-server (MOM) nodes run various part of the Cray software infrastructure. These are Intel E5-2695 v4 nodes with 128 GiB of DDR4 memory. These nodes also run the Cobalt scheduler and execute the user batch scripts. It is critical that users do not put computational or memory intensive tasks within the batch script and instead run those on the compute resources.


The Lustre LNET routers serve as a gateway between the high-speed Aries fabric and the Infiniband FDR storage network. These nodes are Intel Sandy Bridge E5-2670 with 64 GiB of DDR3 memory.


The Cray Data Virtualization Service (DVS) server provide a gateway between the high-speed Aries fabric and other external file systems. The DVS server primarily provide access to the GPFS file systems, such as the home file system. These nodes are physically identical to the LNET nodes, which are Intel Sandy Bridge E5-2670 with 64 GiB of DDR3 memory.

Tier 2

The Tier 2 nodes provide infrastructure to the Cray software stack and aggregate sets of compute nodes. These nodes are physically identical to the MOM nodes and have Intel E5-2695 v4 CPUs with 128 GiB of DDR4 memory.

Compute Nodes

Theta provides only a single compute node type: the Intel Knights Landing 7230 processors with 16 GiB of MCDRAM and 192 GiB of DDR4. These nodes have 64 cores each and each core has 4 SMT hardware threads available.


Cray XC40
Cray DVS
Cray Aries
Intel KNL
Top 500