CDC 7600
Encyclopedia
The CDC 7600 was the Seymour Cray
Seymour Cray
Seymour Roger Cray was an American electrical engineer and supercomputer architect who designed a series of computers that were the fastest in the world for decades, and founded Cray Research which would build many of these machines. Called "the father of supercomputing," Cray has been credited...

-designed successor to the CDC 6600
CDC 6600
The CDC 6600 was a mainframe computer from Control Data Corporation, first delivered in 1964. It is generally considered to be the first successful supercomputer, outperforming its fastest predecessor, IBM 7030 Stretch, by about three times...

, extending Control Data's dominance of the supercomputer
Supercomputer
A supercomputer is a computer at the frontline of current processing capacity, particularly speed of calculation.Supercomputers are used for highly calculation-intensive tasks such as problems including quantum physics, weather forecasting, climate research, molecular modeling A supercomputer is a...

 field into the 1970s. The 7600 ran at 36.4 MHz (27.5 ns clock cycle) and had a 65 Kword primary memory using core and variable-size (up to 512 Kword) secondary memory (depending on site). It was generally about ten times as fast as the CDC 6600, and could deliver about 10 MFLOPS on hand-compiled code, with a peak of 36 MFLOPS. In addition, in benchmark tests in early 1970 it was shown to be slightly faster than its IBM
IBM
International Business Machines Corporation or IBM is an American multinational technology and consulting corporation headquartered in Armonk, New York, United States. IBM manufactures and sells computer hardware and software, and it offers infrastructure, hosting and consulting services in areas...

 rival, the IBM System 360, Model 195. When the system was released in 1969, it carried a price tag around $5 million, more as options and features were added.

Design

After the 6600 started to near production quality, Cray lost interest in it and turned to designing its replacement. Making a machine "somewhat" faster would not be too difficult in the late 1960s; the introduction of integrated circuit
Integrated circuit
An integrated circuit or monolithic integrated circuit is an electronic circuit manufactured by the patterned diffusion of trace elements into the surface of a thin substrate of semiconductor material...

s allowed for denser packing of components, and in turn a high clock speed. Transistor
Transistor
A transistor is a semiconductor device used to amplify and switch electronic signals and power. It is composed of a semiconductor material with at least three terminals for connection to an external circuit. A voltage or current applied to one pair of the transistor's terminals changes the current...

s in general were also getting somewhat faster as the production processes and quality improved. However these sorts of improvements might be expected to make a machine twice as fast, perhaps as much as five times, but not the tenfold increase he demanded. Likewise the 6600 already had a hard time filling its existing ten functional units, so simply adding more parallelism wouldn't help all that much.

In order to solve this problem, Cray turned to the concept of an instruction pipeline
Instruction pipeline
An instruction pipeline is a technique used in the design of computers and other digital electronic devices to increase their instruction throughput ....

. While the 6600 could work on several instructions at once, it had to wait for any one to complete its trip through a functional unit before moving on to the next. For some period of time, the majority of the circuitry in any one unit was not being used. A pipeline improves on this by feeding in the next instruction before the first has completed, thereby having each unit effectively work in "parallel", as well as the machine as a whole. The improvement in performance generally depends on the number of steps the unit takes to complete, for instance, the 6600's divide unit took 10 cycles to complete an instruction, so by pipelining the units it could be expected to gain about 10 times the speed.

Things are never that simple, however. Pipelining requires that the unit's internals can be effectively separated to the point where each step of the operation is running on completely separate circuitry. This is rarely achievable in the real world. Nevertheless, the use of pipelining on the 7600 improved performance over the 6600 by a factor of about 3.

As always, Cray's design also focussed on packaging to reduce size, shorten signal paths, and thereby increase operating frequency. For the 7600 each circuit module actually consisted of up to six PC boards, each one stuffed with subminiature resistors, diodes, and transistors. The six boards were stacked up and then interconnected along their edges, making for a very compact, but basically unrepairable module.

However the same dense packing also led to the machine's biggest problem—heat. For the 7600, Cray once again turned to his refrigeration engineer, Dean Roush, formerly of the Amana company. Roush added an aluminum plate to the back of each side of the cordwood stack, which were in turn cooled by a liquid freon system running through the core of the machine. Since the system was mechanical and therefore prone to failure, the 7600 was redesigned into a large "C" shape to allow access to the modules on either side of the cooling piping by walking into the inside of the C and opening the cabinet.

Relationship with the CDC 6600

Although the 7600 shared many features of the 6600, including hardware, instructions, and its 60-bit word size, it was not object-code compatible with the CDC 6600. In addition, it was not entirely source-code (COMPASS
COMPASS
COMPASS is an acronym for COMPrehensive ASSembler. COMPASS is any of a family of macro assembly languages on Control Data Corporation's 3000 series, and on the 60-bit CDC 6000 series, 7600 and Cyber 70 and 170 series mainframe computers...

) compatible, as some instructions in the 7600 did not exist in the 6600, and vice-versa. It had originally been named the CDC 6800, but was changed to 7600 when Cray decided it could not be completely compatible. However, due to the 7600's operating system design, the 6600 and 7600 shared a "uniform software environment" despite the low-level differences.

In fact, from a high-level perspective, the 7600 was quite similar to the 6600. At the time computer memory could be arranged in blocks with independent access paths, and Cray's designs used this to their advantage. While most machines would use a single CPU to run all the functionality of the system, Cray realized that this meant each memory block spent a considerable amount of time idle while the CPU was processing instructions and accessing other blocks. In order to take advantage of this, the 6600 and 7600 left mundane housekeeping tasks, printing output or reading punched card
Punched card
A punched card, punch card, IBM card, or Hollerith card is a piece of stiff paper that contains digital information represented by the presence or absence of holes in predefined positions...

s for instance, to a series of ten smaller 12-bit machines based on the CDC 160A
CDC 160A
The CDC 160 and CDC 160-A were 12-bit minicomputers built by Control Data Corporation from 1960 to 1965. The 160 was designed by Seymour Cray - reportedly over a long three-day weekend...

 known as Peripheral Processors or PP's. For any given cycle of the machine one of the PP's was in control, feeding data into the memory while the main processor was crunching numbers. When the cycle completed, the next PP was given control. In this way the memory always held up-to-date information for the main processor to work on (barring delays in the external devices themselves), eliminating delays on data as well as allowing the CPU to be built for mathematical performance and nothing else. The PPU could have been called a very smart "communications channel".

Like the 6600, the 7600 used 60-bit words with instructions that were generally 15-bits in length (although there were longer versions). However the instruction set itself had changed to reflect the new internal memory layout, thereby rendering it incompatible with the earlier 6600. The machines were similar enough to make porting of compiler
Compiler
A compiler is a computer program that transforms source code written in a programming language into another computer language...

s and operating system
Operating system
An operating system is a set of programs that manage computer hardware resources and provide common services for application software. The operating system is the most important type of system software in a computer system...

s possible without too much trouble. The machine initially did not come with software; sites had to be willing to write their own operating system, like NLTSS
NLTSS
NLTSS, the Network Livermore Timesharing System, also sometimes known as the New Livermore Time Sharing System was an operating system that was actively developed at Lawrence Livermore Laboratory from 1979 until about 1988, though it continued to run production applications until 1995...

, NCAROS, and others; and compilers like LRLTRAN [Livermore's version of Fortran with dynamic memory management and other non-standard features].

Reception and Usage

From the period from about 1969 to 1975, the CDC 7600 was generally regarded as the fastest computer in the world, except for specialized units. However, even with the advanced mechanicals and cooling the 7600 was prone to failure. Both LLNL and NCAR reported that the machine would break down at least once a day, often 4 or 5 times. Acceptance at installation sites took years while the bugs were worked out, and while the machine generally sold well enough given its "high end" niche, it is unlikely the machine generated any sort of real profits for CDC. The successor CDC 8600
CDC 8600
The CDC 8600 was the last of Seymour Cray's supercomputer designs while working for the Control Data Corporation. The "natural successor" to the CDC 6600 and CDC 7600, the 8600 was intended to be about 10 times as fast as the 7600, already the fastest computer on the market.Development started in...

 was never completed, and Seymour Cray went on to form his own company, Cray Research.

One surviving 7600 is partially on display at the Computer History Museum
Computer History Museum
The Computer History Museum is a museum established in 1996 in Mountain View, California, USA. The Museum is dedicated to preserving and presenting the stories and artifacts of the information age, and exploring the computing revolution and its impact on our lives.-History:The museum's origins...

. Its sheer size allows only 2 corner units to be shown. The rest is in storage.

Another 7600 is on display at the Chippewa Falls Museum of Industry and Technology, along with its console and a tape controller.

External links

  • Neil R. Lincoln with 18 Control Data Corporation (CDC) engineers on computer architecture and design, Charles Babbage Institute
    Charles Babbage Institute
    The Charles Babbage Institute is a research center at the University of Minnesota specializing in the history of information technology, particularly the history since 1935 of digital computing, programming/software, and computer networking....

    , University of Minnesota. Engineers include Robert Moe, Wayne Specker, Dennis Grinna, Tom Rowan, Maurice Hutson, Curt Alexander, Don Pagelkopf, Maris Bergmanis, Dolan Toth, Chuck Hawley, Larry Krueger, Mike Pavlov, Dave Resnick, Howard Krohn, Bill Bhend, Kent Steiner, Raymon Kort, and Neil R. Lincoln. Discussion topics include CDC 1604
    CDC 1604
    The CDC 1604 was a 48-bit computer designed and manufactured by Seymour Cray and his team at the Control Data Corporation. The 1604 is known as the first commercially successful transistorized computer. Legend has it that the 1604 designation was chosen by adding CDC's first street address to...

    , CDC 6600
    CDC 6600
    The CDC 6600 was a mainframe computer from Control Data Corporation, first delivered in 1964. It is generally considered to be the first successful supercomputer, outperforming its fastest predecessor, IBM 7030 Stretch, by about three times...

    , CDC 7600, CDC 8600
    CDC 8600
    The CDC 8600 was the last of Seymour Cray's supercomputer designs while working for the Control Data Corporation. The "natural successor" to the CDC 6600 and CDC 7600, the 8600 was intended to be about 10 times as fast as the 7600, already the fastest computer on the market.Development started in...

    , CDC STAR-100
    CDC STAR-100
    The STAR-100 was a vector supercomputer designed, manufactured, and marketed by Control Data Corporation . It was one of the first machines to use a vector processor to improve performance on appropriate scientific applications....

     and Seymour Cray
    Seymour Cray
    Seymour Roger Cray was an American electrical engineer and supercomputer architect who designed a series of computers that were the fastest in the world for decades, and founded Cray Research which would build many of these machines. Called "the father of supercomputing," Cray has been credited...

    .
  • Presentation of the CDC 7600 and other machines designed by Seymour Cray – by C. Gordon Bell
    Gordon Bell
    C. Gordon Bell is an American computer engineer and manager. An early employee of Digital Equipment Corporation 1960–1966, Bell designed several of their PDP machines and later became Vice President of Engineering 1972-1983, overseeing the development of the VAX...

    of Microsoft Research (formerly of DEC)
  • SDC Computer Gallery
  • Computer History Museum
  • Chippewa Falls Museum of Industry and Technology
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