Editing Alliant Computer Systems (section)

===1980s===
Alliant was founded, as Dataflow Systems, in May 1982 by Ron Gruner, [[Craig Mundie]] and Rich McAndrew<ref name="Livingston2008">{{cite book|last=Livingston|first=Jessica|authorlink=Jessica Livingston|title=Founders at Work: Stories of Startups' Early Days|url=https://books.google.com/books?id=ktm885vGIXEC&pg=PA427|date=1 November 2008|publisher=Apress|isbn=978-1-4302-1077-1|page=427}}</ref> to produce machines for scientific and engineering users who needed smaller, less costly machines than offerings from [[Cray Computer]] and similar high-end vendors. Machines that addressed this market segment later became known as [[minisupercomputer]]s. At the time there was a huge gap on the price/performance curve as a highly configured [[VAX 11/780]] had a performance of about a [[million instructions per second|MIP]] and [[megaflop|MegaFLOP]] for around $1M USD and a Cray-1S or Cray 1M over $10M USD.

Alliant's first machines were announced in 1985, starting with the FX series. The FX series consisted of four types of 18" x 18" boards: Computational Elements, or CEs, System Cache, Interactive Processor (IP) Cache, and Memory Modules. Each board plugged into a [[backplane]] using a special high-density connector. The caches and memory modules all communicated with each other over a 2 x 64-bit bus called the DMB (Dataflow Memory Bus). The backplane was an active backplane and it contained an 8 x 4 crossbar switch (FX/8) that allowed any CE to connect to one of four cache ports, two on each System Cache. Total cache bandwidth was 376&nbsp;[[MB/s]].

The CEs included a set of [[Weitek]] 1064/1065 [[floating point unit|FPU]]'s and several custom designed support chips to implement a custom [[vector processor]]. The [[Scalar processor|scalar]] [[instruction set]] was based upon the popular [[Motorola 68000 family|Motorola 68000]] architecture. The floating point instruction set, vector instruction set, and concurrency instruction set were all custom [[co-processor]] instruction sets designed by Alliant. The shared system cache and a special concurrency bus implemented low [[Latency_(engineering)#Computer_hardware_and_software_systems|latency]] concurrency control that could be exploited automatically by [[high-level language]] [[compiler]]s to provide [[Data parallelism|data-parallel]] processing among the CEs. The scalar instruction cycle time for the original CE was 170&nbsp;ns, the vector processor was twice as fast as the scalar processor with a cycle time of 85&nbsp;ns.

Each IP Cache had three ports that connected via [[ribbon cable]]s to [[Interactive processing|Interactive Processors]], IPs, which used [[Motorola 68012]]'s and, subsequently [[Motorola 68020]]'s and then [[Motorola 68030]]'s with 4&nbsp;MB of local RAM in a Multibus form factor plugged into a 13 slot Multibus chassis.

Memory modules were 8&nbsp;MB each and four way interleaved with ECC. Read bandwidth was 188&nbsp;MB/s.

Like many early [[multiprocessing]] systems, the FX series ran a version of [[BSD Unix|4.2 BSD Unix]] on the IPs and CEs, known as Concentrix which initially added multiprocessor support and new VM and IO sub-systems. Subsequent releases added features such as the first striped Track File System (TFS) and support for real time scheduling (FX/RT).

Systems were numerated for the largest potential number of CEs inside, the FX/1, FX/4 and FX/8. Alliant machines were fairly small, the FX/1 was about the size of a large full-height PC, while the FX/8 was smaller than a [[VAX-11|VAX-11/780]], about the size of a large [[photocopier]]. All the systems were [[Computer_cooling#Air_cooling|air-cooled]]. The speed of an FX/1 was about 2.5 MIPS ([[million instructions per second]]) and compared favorably to the 1 MIPS [[VAX-11/780]]. A fully populated eight CE FX/8, with eight times the aggregate MIPS, was in practice around five times faster than the FX/1 at solving problems that allowed a high degree of [[parallel computation]] (see [[Amdahls law|Amdahl's law]]).

A second series of FX machines, introduced in early 1988, replaced the CE with pin compatible new custom hardware known as the ''Advanced Computational Element'' (ACE). The Weitek FPUs were replaced by a floating point chipset made by [[Bipolar Integrated Technology]] which formed the core of a redesigned vector processor with 32 64-bit vector elements, 8 64-bit scalar floating point [[processor register|registers]], 8 32-bit integer registers, and 8 32-bit address registers. The new vector processor increased vector processing speed by reducing the in-register cycle time to 42&nbsp;ns. The scalar instruction cycle time, cache and memory bandwidth remained the same. The ACE, with its higher level of integration using more advanced [[application-specific integrated circuit|ASIC]]s, also required less [[printed circuit board]] space allowing it to return to the 18x18 inch square profile used by the other system boards in the main chassis. These were used in the FX/40, FX/80 and VFX machines. In addition, because of the pin compatibility, existing FX/4 and FX/8 systems could be field upgraded to FX/40 and FX/80 configurations by simple replacement of CE's with ACE's along with an update to the microcode file on the system disk. However systems of mixed configurations of CEs and ACEs were not supported. The smaller FX/1, because of restrictions in chassis cooling, could not be upgraded.

Alliant offered a number of software packages for its machines, including a solver for linear equations (FX/Skyline Solver), a C compiler (FX/C compiler), and scientific libraries (FX/Linpack and FX/Eispack).<ref name="Gibson1987">{{citation|last=Gibson|first=Stanley|title=Alliant adds compiler tools|url=https://books.google.com/books?id=mUSIMiurpfYC&pg=PP29|volume=21|date=2 November 1987|publisher=IDG Enterprise|page=29|issn=0010-4841|work=Computerworld|issue=44}}</ref>