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Designer | Cray |
---|---|
Bits | 64-bit |
Introduced | 2005 |
Version | 3rd generation of Tera MTA |
Endianness | Big-endian |
Predecessor | Cray MTA-2 |
Successor | Cray XMT2 |
Registers | |
32 general-purpose per stream (4096 per CPU) 8 target per stream (1024 per CPU) |
Cray XMT (Cray eXtreme MultiThreading,[1] codenamed Eldorado[2]) is a scalable multithreaded shared memory supercomputer architecture by Cray, based on the third generation of the Tera MTA architecture, targeted at large graph problems (e.g. semantic databases, big data, pattern matching).[3][4][5] Presented in 2005, it supersedes the earlier unsuccessful Cray MTA-2. It uses the Threadstorm3 CPUs inside Cray XT3 blades. Designed to make use of commodity parts and existing subsystems for other commercial systems, it alleviated the shortcomings of Cray MTA-2's high cost of fully custom manufacture and support.[2] It brought various substantial improvements over Cray MTA-2, most notably nearly tripling the peak performance, and vastly increased maximum CPU count to 8,192 and maximum memory to 128 TB, with a data TLB of maximal 512 TB.[2][3]
Cray XMT uses a scrambled[3] content-addressable memory[6] model on DDR1 ECC modules to implicitly load-balance memory access across the whole shared global address space of the system.[5] Use of 4 additional Extended Memory Semantics bits (full/empty, forwarding and 2 trap bits) per 64-bit memory word enables lightweight, fine-grained synchronization on all memory.[7] There are no hardware interrupts and hardware threads are allocated by an instruction, not the OS.[5][7]
Front-end (login, I/O, and other service nodes, utilizing AMD Opteron processors and running SLES Linux) and back-end (compute nodes, utilizing Threadstorm3 processors and running MTK, a simple BSD Unix-based microkernel[3]) communicate through the LUC (Lightweight User Communication) interface, a RPC-style bidirectional client/server interface.[1][5]
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