Supercomputers/Systems/Louhi
Finland · operational · hpc
Louhi
Also known as CSC Louhi Cray XT4/XT5
Operated by CSC .
Phase 1 seed dataset, compiled by hand. These rows were built from public operator, laboratory and vendor sources. A mechanical second-reader pass has since fetched every cited source: 1263 of 1345 systems have a readable citation that names them, and 56 are genuinely weakly sourced. Every claim carries its source and a confidence tier. Treat anything below verified as a lead, not a citation.
Measured performance
- Rmax
- 76.51 TFlop/s
- Rpeak
- 99.51 TFlop/s
- Rmax ÷ Rpeak
- 76.9%
- Cores
- 10,816
- Power
- 515 kW
- Per watt
- 0.1 GF/W
Figures are as last publicly reported for the configuration described below, not a live measurement. Where a system was upgraded in place, the post-upgrade configuration is shown and the earlier one appears in the timeline.
What this machine is made of
One row per supplier relationship. “Supplier at build” is the company that shipped the part at the time; where that company has since been acquired, the parent it rolls up to today is shown beside it. That distinction is what makes ticker-level aggregation possible across a thirty-year dataset.
| Role | Part | Supplier at build | Quantity | Confidence | Source |
|---|---|---|---|---|---|
| Integrator | - Cray XT4 and XT5 system | Cray HPENYSE
rolls up to Hewlett Packard Enterprise | - | Reported | top500.orgtheregister.com |
| CPU | - AMD Opteron quad-core 2.3 GHz | AMD | - | Reported | top500.orgtheregister.com |
| Interconnect | - Cray SeaStar XT interconnect | Cray HPENYSE
rolls up to Hewlett Packard Enterprise | - | Reported | theregister.comtop500.org |
| Operating system | Cray Linux Environment Operating systems Linux, Cray-customised · Proprietary layer over open-source Linux Cray Compute Node Linux (CNL) | Cray HPENYSE
rolls up to Hewlett Packard Enterprise | - | Reported | top500.org |
The read
CSC's Cray XT4/XT5 supercomputer in Espoo. The Register (July 2012) says it came online in spring 2007 and was upgraded two years later to a mix of XT4 and XT5 nodes with quad-core Opterons and the SeaStar interconnect, 10,864 cores, about 76.5 TFlop/s sustained and 102 TFlop/s peak. TOP500 lists the system (2008 installation year, CNL operating system) on several lists from November 2008 (32nd, 10,816 cores, 76.51 TFlop/s Rmax, 99.51 TFlop/s Rpeak, 515 kW) to November 2011 (a second entry, TOP500 system 176489, at 10,864 cores). The Register article also describes CSC's then-planned HP cluster and Cray successors in Kajaani. The retirement date was not found; the status date is the last list appearance.
Timeline
Public list appearances
Pointers only: rank and edition, linking to the canonical entry. We do not reproduce list tables. See sourcing policy.
Change history
- 2026-10-09 Added Louhi
Source check
We fetched this system's own citations and recorded whether each page actually mentions it. This is a corroboration signal, not a fact check, and it is published so you can see how well the sourcing holds up rather than take it on trust.
| Cited source | Result | Found on the page |
|---|---|---|
| theregister.com | names system only | - |
| top500.org | does not name this system | - |
Checked 2026-10-13 by pnpm verify. Re-run it and the table changes with the web.
Further reading
Operating a supercomputer
Acceptance testing, why "installed" and "in production" are six months apart, and the machine lifecycle.
Inside a node
Latency-optimised versus throughput-optimised processors, NUMA, and the end of the host-to-device copy.
The interconnect
Topologies, why latency and tail behaviour matter more than bandwidth, and how the fabric market consolidated.