Supercomputer architecture

Approaches to supercomputer architecture have taken dramatic turns since the earliest systems were introduced in the 1960s. Early supercomputer architectures pioneered by Seymour Cray relied on compact innovative designs and local parallelism to achieve superior computational peak performance. However, in time the demand for increased computational power ushered in the age of massively parallel systems. Approaches to supercomputer architecture have taken dramatic turns since the earliest systems were introduced in the 1960s. Early supercomputer architectures pioneered by Seymour Cray relied on compact innovative designs and local parallelism to achieve superior computational peak performance. However, in time the demand for increased computational power ushered in the age of massively parallel systems. While the supercomputers of the 1970s used only a few processors, in the 1990s, machines with thousands of processors began to appear and by the end of the 20th century, massively parallel supercomputers with tens of thousands of 'off-the-shelf' processors were the norm. Supercomputers of the 21st century can use over 100,000 processors (some being graphic units) connected by fast connections. Throughout the decades, the management of heat density has remained a key issue for most centralized supercomputers. The large amount of heat generated by a system may also have other effects, such as reducing the lifetime of other system components. There have been diverse approaches to heat management, from pumping Fluorinert through the system, to a hybrid liquid-air cooling system or air cooling with normal air conditioning temperatures. Systems with a massive number of processors generally take one of two paths: in one approach, e.g., in grid computing the processing power of a large number of computers in distributed, diverse administrative domains, is opportunistically used whenever a computer is available. In another approach, a large number of processors are used in close proximity to each other, e.g., in a computer cluster. In such a centralized massively parallel system the speed and flexibility of the interconnect becomes very important, and modern supercomputers have used various approaches ranging from enhanced Infiniband systems to three-dimensional torus interconnects. Since the late 1960s the growth in the power and proliferation of supercomputers has been dramatic, and the underlying architectural directions of these systems have taken significant turns. While the early supercomputers relied on a small number of closely connected processors that accessed shared memory, the supercomputers of the 21st century use over 100,000 processors connected by fast networks. Throughout the decades, the management of heat density has remained a key issue for most centralized supercomputers. Seymour Cray's 'get the heat out' motto was central to his design philosophy and has continued to be a key issue in supercomputer architectures, e.g., in large-scale experiments such as Blue Waters. The large amount of heat generated by a system may also have other effects, such as reducing the lifetime of other system components. There have been diverse approaches to heat management, e.g., the Cray 2 pumped Fluorinert through the system, while System X used a hybrid liquid-air cooling system and the Blue Gene/P is air-cooled with normal air conditioning temperatures. The heat from the Aquasar supercomputer is used to warm a university campus. The heat density generated by a supercomputer has a direct dependence on the processor type used in the system, with more powerful processors typically generating more heat, given similar underlying semiconductor technologies. While early supercomputers used a few fast, closely packed processors that took advantage of local parallelism (e.g., pipelining and vector processing), in time the number of processors grew, and computing nodes could be placed further away,e.g., in a computer cluster, or could be geographically dispersed in grid computing. As the number of processors in a supercomputer grows, 'component failure rate' begins to become a serious issue. If a supercomputer uses thousands of nodes, each of which may fail once per year on the average, then the system will experience several node failures each day. As the price/performance of general purpose graphic processors (GPGPUs) has improved, a number of petaflop supercomputers such as Tianhe-I and Nebulae have started to rely on them. However, other systems such as the K computer continue to use conventional processors such as SPARC-based designs and the overall applicability of GPGPUs in general purpose high performance computing applications has been the subject of debate, in that while a GPGPU may be tuned to score well on specific benchmarks its overall applicability to everyday algorithms may be limited unless significant effort is spent to tune the application towards it. However, GPUs are gaining ground and in 2012 the Jaguar supercomputer was transformed into Titan by replacing CPUs with GPUs.