The CDC 6600 was the flagship of the 6000 series of

mainframe computer A mainframe computer, informally called a mainframe or big iron, is a computer used primarily by large organizations for critical applications like bulk data processing for tasks such as censuses, industry and consumer statistics, enterprise ...

systems manufactured by

Control Data Corporation Control Data Corporation (CDC) was a mainframe and supercomputer company that in the 1960s was one of the nine major U.S. computer companies, which group included IBM, the Burroughs Corporation, and the Digital Equipment Corporation (DEC), the N ...

. Generally considered to be the first successful

supercomputer A supercomputer is a type of computer with a high level of performance as compared to a general-purpose computer. The performance of a supercomputer is commonly measured in floating-point operations per second (FLOPS) instead of million instruc ...

, it outperformed the industry's prior recordholder, the

IBM 7030 Stretch The IBM 7030, also known as Stretch, was IBM's first transistorized supercomputer. It was the fastest computer in the world from 1961 until the first CDC 6600 became operational in 1964."Designed by Seymour Cray, the CDC 6600 was almost three tim ...

, by a factor of three."Designed by Seymour Cray, the CDC 6600 was almost three times faster than the next fastest machine of its day, the IBM 7030 Stretch." With performance of up to three

megaFLOPS Floating point operations per second (FLOPS, flops or flop/s) is a measure of computer performance in computing, useful in fields of scientific computations that require floating-point calculations. For such cases, it is a more accurate measur ...

, the CDC 6600 was the world's fastest computer from 1964 to 1969, when it relinquished that status to its successor, the

CDC 7600 The CDC 7600 was designed by Seymour Cray to be the successor to the CDC 6600, extending Control Data Corporation, Control Data's dominance of the supercomputer field into the 1970s. The 7600 ran at 36.4 MHz (27.5 ns clock cycle) and had ...

."The 7600 design lasted longer than any other supercomputer design. It had the highest performance of any computer from its introduction in 1969 till the introduction of the

Cray 1 The Cray-1 was a supercomputer designed, manufactured and marketed by Cray Research. Announced in 1975, the first Cray-1 system was installed at Los Alamos National Laboratory in 1976. Eventually, eighty Cray-1s were sold, making it one of the m ...

in 1976." The first CDC 6600s were delivered in 1965 to Livermore and Los Alamos. They quickly became a must-have system in high-end scientific and mathematical computing, with systems being delivered to

Courant Institute of Mathematical Sciences The Courant Institute of Mathematical Sciences (commonly known as Courant or CIMS) is the mathematics research school of New York University (NYU). Founded in 1935, it is named after Richard Courant, one of the founders of the Courant Institute ...

CERN The European Organization for Nuclear Research, known as CERN (; ; ), is an intergovernmental organization that operates the largest particle physics laboratory in the world. Established in 1954, it is based in Meyrin, western suburb of Gene ...

, the

Lawrence Radiation Laboratory Lawrence may refer to: Education Colleges and universities * Lawrence Technological University, a university in Southfield, Michigan, United States * Lawrence University, a liberal arts university in Appleton, Wisconsin, United States Preparator ...

, and many others. At least 100 were delivered in total. A CDC 6600 is on display at the

Computer History Museum The Computer History Museum (CHM) is a computer museum in Mountain View, California. The museum presents stories and artifacts of Silicon Valley and the Information Age, and explores the Digital Revolution, computing revolution and its impact ...

Mountain View, California Mountain View is a city in Santa Clara County, California, United States, part of the San Francisco Bay Area. Named for its views of the Santa Cruz Mountains, the population was 82,376 at the 2020 United States census, 2020 census. Mountain V ...

. The only running CDC 6000 series machine was restored by Living Computers: Museum + Labs, however the museum has permanently closed.

History and impact

CDC's first products were based on the machines designed at

Engineering Research Associates Engineering Research Associates, commonly known as ERA, was a pioneering computer firm from the 1950s. ERA became famous for their numerical computers, but as the market expanded they became better known for their drum memory systems. They were ...

(ERA), which

Seymour Cray Seymour Roger Cray (September 28, 1925 – October 5, 1996)
– was an American

CDC 1604 The CDC 1604 is a 48-bit computer designed and manufactured by Seymour Cray and his team at the Control Data Corporation (CDC). The 1604 is known as one of the first commercially successful transistorized computers. (The IBM 7090 was delivered ...

, one of the first commercial transistor-based computers, and one of the fastest machines on the market. Management was delighted, and made plans for a new series of machines that were more tailored to business use; they would include instructions for character handling and record keeping for instance. Cray was not interested in such a project and set himself the goal of producing a new machine that would be 50 times faster than the 1604. When asked to complete a detailed report on plans at one and five years into the future, he wrote back that his five-year goal was "to produce the largest computer in the world", "largest" at that time being synonymous with "fastest", and that his one-year plan was "to be one-fifth of the way". Taking his core team to new offices near the original CDC headquarters, they started to experiment with higher quality versions of the "cheap"

transistor A transistor is a semiconductor device used to Electronic amplifier, amplify or electronic switch, switch electrical signals and electric power, power. It is one of the basic building blocks of modern electronics. It is composed of semicondu ...

s Cray had used in the 1604. After much experimentation, they found that there was simply no way the

germanium Germanium is a chemical element; it has Symbol (chemistry), symbol Ge and atomic number 32. It is lustrous, hard-brittle, grayish-white and similar in appearance to silicon. It is a metalloid or a nonmetal in the carbon group that is chemically ...

-based transistors could be run much faster than those used in the 1604. The "business machine" that management had originally wanted, now forming as the

CDC 3000 series The CDC 3000 series ("thirty-six hundred" or "thirty-one hundred") are a family of mainframe computers from Control Data Corporation (CDC). The first member, the CDC 3600, was a 48-bit system introduced in 1963. The same basic design led to the c ...

, pushed them about as far as they could go. Cray then decided the solution was to work with the then-new

silicon Silicon is a chemical element; it has symbol Si and atomic number 14. It is a hard, brittle crystalline solid with a blue-grey metallic lustre, and is a tetravalent metalloid (sometimes considered a non-metal) and semiconductor. It is a membe ...

-based transistors from

Fairchild Semiconductor Fairchild Semiconductor International, Inc. was an American semiconductor company based in San Jose, California. It was founded in 1957 as a division of Fairchild Camera and Instrument by the " traitorous eight" who defected from Shockley Semi ...

, which were just coming onto the market and offered dramatically improved switching performance. During this period, CDC grew from a startup to a large company and Cray became increasingly frustrated with what he saw as ridiculous management requirements. Things became considerably more tense in 1962 when the new

CDC 3600 The CDC 3000 series ("thirty-six hundred" or "thirty-one hundred") are a family of mainframe computer, mainframe computers from Control Data Corporation (CDC). The first member, the CDC 3600, was a 48-bit computing, 48-bit system introduced in 196 ...

started to near production quality, and appeared to be exactly what management wanted, when they wanted it. Cray eventually told CDC's CEO, William Norris that something had to change, or he would leave the company. Norris felt he was too important to lose, and gave Cray the green light to set up a new laboratory wherever he wanted. After a short search, Cray decided to return to his home town of

Chippewa Falls, Wisconsin Chippewa Falls () is a city located on the Chippewa River (Wisconsin), Chippewa River in Chippewa County, Wisconsin, United States. The population was 14,731 in the 2020 United States census, 2020 census. Incorporated as a city in 1869, it is the ...

, where he purchased a block of land and started up a new laboratory. Although this process introduced a fairly lengthy delay in the design of his new machine, once in the new laboratory, without management interference, things started to progress quickly. By this time, the new transistors were becoming quite reliable, and modules built with them tended to work properly on the first try. The 6600 began to take form, with Cray working alongside Jim Thornton, system architect and "hidden genius" of the 6600. More than 100 CDC 6600s were sold over the machine's lifetime (1964 to 1969). Many of these went to various

nuclear weapon A nuclear weapon is an explosive device that derives its destructive force from nuclear reactions, either fission (fission or atomic bomb) or a combination of fission and fusion reactions (thermonuclear weapon), producing a nuclear exp ...

-related laboratories, and quite a few found their way into university computing laboratories. A CDC 6600 was used to disprove

Euler's sum of powers conjecture In number theory, Euler's conjecture is a disproved conjecture related to Fermat's Last Theorem. It was proposed by Leonhard Euler in 1769. It states that for all integers and greater than 1, if the sum of many th powers of positive integers ...

in an early example of direct numerical search. Cray immediately turned his attention to its replacement, this time setting a goal of ten times the performance of the 6600, delivered as the

. The later

CDC Cyber The CDC Cyber range of mainframe computer, mainframe-class supercomputers were the primary products of Control Data Corporation (CDC) during the 1970s and 1980s. In their day, they were the computer architecture of choice for scientific and ma ...

70 and 170 computers were very similar to the CDC 6600 in overall design and were nearly completely backwards compatible. The 6600 was three times faster than the previous record-holder, the

; this alarmed

IBM International Business Machines Corporation (using the trademark IBM), nicknamed Big Blue, is an American Multinational corporation, multinational technology company headquartered in Armonk, New York, and present in over 175 countries. It is ...

. Then-CEO Thomas Watson Jr. wrote a memo to his employees on August 28, 1963: "Last week, Control Data ... announced the 6600 system. I understand that in the laboratory developing the system there are only 34 people including the janitor. Of these, 14 are engineers and 4 are programmers ... Contrasting this modest effort with our vast development activities, I fail to understand why we have lost our industry leadership position by letting someone else offer the world's most powerful computer." Cray's reply was sardonic: "It seems like Mr. Watson has answered his own question."

Description

Typical machines of the 1950s and 1960s used a single

central processing unit A central processing unit (CPU), also called a central processor, main processor, or just processor, is the primary Processor (computing), processor in a given computer. Its electronic circuitry executes Instruction (computing), instructions ...

(CPU) to drive the entire system. A typical program would first load data into memory (often using pre-rolled library code), process it, and then write it back out. This required the CPUs to be fairly complex in order to handle the complete set of instructions they would be called on to perform. A complex CPU implied a large CPU, introducing signalling delays while information flowed between the individual modules making it up. These delays set a maximum upper limit on performance, as the machine could only operate at a cycle speed that allowed the signals time to arrive at the next module. Cray took another approach. In the 1960s, CPUs generally ran slower than the

main memory Computer data storage or digital data storage is a technology consisting of computer components and recording media that are used to retain digital data. It is a core function and fundamental component of computers. The central processin ...

to which they were attached. For instance, a processor might take 15 cycles to multiply two numbers, while each memory access took only one or two cycles. This meant there was a significant time where the main memory was idle. It was this idle time that the 6600 exploited. The CDC 6600 used a simplified central processor (CP) that was designed to run mathematical and logic operations as rapidly as possible, which demanded it be built as small as possible to reduce the length of wiring and the associated signalling delays. This led to the machine's (typically) cross-shaped main chassis with the circuit boards for the CPU arranged close to the center, and resulted in a much smaller CPU. Combined with the faster switching speeds of the silicon transistors, the new CPU ran at 10 MHz (100 ns cycle time), about ten times faster than other machines on the market. In addition to the clock being faster, the simple processor executed instructions in fewer clock cycles; for instance, the CPU could complete a multiplication in ten cycles. Supporting the CPU were ten 12-bit 4 KiB peripheral processors (PPs), each with access to a common pool of 12 input/output (I/O) channels, that handled input and output, as well as controlling what data were sent into central memory for processing by the CP. The PPs were designed to access memory during the times when the CPU was busy performing operations. This allowed them to perform

input/output In computing, input/output (I/O, i/o, or informally io or IO) is the communication between an information processing system, such as a computer, and the outside world, such as another computer system, peripherals, or a human operator. Inputs a ...

essentially for free in terms of central processing time, keeping the CPU busy as much as possible. The 6600's CP used a 60-bit word and a

ones' complement The ones' complement of a binary number is the value obtained by inverting (flipping) all the bits in the Binary number, binary representation of the number. The name "ones' complement" refers to the fact that such an inverted value, if added t ...

representation of integers, something that later CDC machines would use into the late 1980s, making them the last systems besides some

digital signal processor A digital signal processor (DSP) is a specialized microprocessor chip, with its architecture optimized for the operational needs of digital signal processing. DSPs are fabricated on metal–oxide–semiconductor (MOS) integrated circuit chips. ...

s to use this architecture. Later, CDC offered options as to the number and type of CPs, PPs and channels, e.g., the CDC 6700 had two central processors, a 6400 CP and a 6600 CP. While other machines of its day had elaborate

front panel A front panel was used on early electronic computers to display and allow the alteration of the state of the machine's internal CPU register, registers and computer memory, memory. The front panel usually consisted of arrays of electric light, ...

s to control them, the 6600 has only a ''dead start panel''. There is a dual CRT system console, but it is controlled by the operating system and neither controls nor displays the hardware directly. The entire 6600 machine contained approximately 400,000 transistors.

Peripheral processors

The CPU could only execute a limited number of simple instructions. A typical CPU of the era had a complex instruction set, which included instructions to handle all the normal "housekeeping" tasks, such as memory access and

. Cray instead implemented these instructions in separate, simpler processors dedicated solely to these tasks, leaving the CPU with a much smaller instruction set. This was the first of what later came to be called

reduced instruction set computer In electronics and computer science, a reduced instruction set computer (RISC) is a computer architecture designed to simplify the individual instructions given to the computer to accomplish tasks. Compared to the instructions given to a com ...

(RISC) design. By allowing the CPU, peripheral processors (PPs) and I/O to operate in parallel, the design considerably improved the performance of the machine. Under normal conditions a machine with several processors would also cost a great deal more. Key to the 6600's design was to make the I/O processors, known as ''peripheral processors'' (PPs), as simple as possible. The PPs were based on the simple 12-bit CDC 160-A, which ran much slower than the CPU, gathering up data and transmitting it as bursts into main memory at high speed via dedicated hardware. The 10 PPs were implemented virtually; there was CPU hardware only for a single PP. This CPU hardware was shared and operated on 10 PP register sets which represented each of the 10 PP ''states'' (similar to modern multithreading processors). The PP '' register barrel'' would "rotate", with each PP register set presented to the "slot" which the actual PP CPU occupied. The shared CPU would execute all or some portion of a PP's instruction whereupon the barrel would "rotate" again, presenting the next PP's register set (state). Multiple "rotations" of the barrel were needed to complete an instruction. A complete barrel "rotation" occurred in 1000 nanoseconds (100 nanoseconds per PP), and an instruction could take from one to five "rotations" of the barrel to be completed, or more if it was a data transfer instruction.

Instruction-set architecture of CP

The basis for the 6600 CPU is what would later be called a

RISC In electronics and computer science, a reduced instruction set computer (RISC) is a computer architecture designed to simplify the individual instructions given to the computer to accomplish tasks. Compared to the instructions given to a comp ...

system, one in which the processor is tuned to do instructions that are comparatively simple and have limited and well-defined access to memory. The philosophy of many other machines was toward using instructions which were complicated — for example, a single instruction which would fetch an operand from memory and add it to a value in a register. Instructions for the CP are either 15 bits split into 5 3-bit fields designated as f, m, i, j and k or 30 bits split into 3-bit f, m, i and j and an 18-bit K field. The function (f) and modifier (m) usually specify the opcode, although in some cases, the register number is part of a 9-bit opcode. Most 15-bit instructions perform an operation on two registers and store the result in a third (i) register. Most 30-bit instructions perform an operation on a register and a constant and store the reult in a second (i) register. The CP has no explicit load and store instructions, and only jumps and the SAi instructions reference memory. An SAi instruction reads from central memory into an associated X register when i is 1-5 and writes from it when i is 6 or 7. Thus, in the CP, adding from memory would require two instructions. While slower in theory due to the additional instruction, the fact that in well-scheduled code, multiple instructions could be processing in parallel offloaded this expense. This simplification also forced programmers to be very aware of their memory accesses, and therefore code deliberately to reduce them as much as possible. The CDC 6600 CP, being a three-address machine, allows for the specification of all three operands.

Models

The

CDC 6000 series The CDC 6000 series is a discontinued family of mainframe computers manufactured by Control Data Corporation in the 1960s. It consisted of the CDC 6200, CDC 6300, #Versions, CDC 6400, #Versions, CDC 6500, CDC 6600 and #Versions, CDC 6700 computers, ...

included four basic models, the CDC 6400, the CDC 6500, the CDC 6600, and the CDC 6700. The models of the 6000 series differed only in their CPUs, which were of two kinds, the 6400 CPU and the 6600 CPU. The 6400 CPU had a unified arithmetic unit, rather than discrete ''functional units''. As such, it could not overlap instructions' execution times. For example, in a 6400 CPU, if an add instruction immediately followed a multiply instruction, the add instruction could not be started until the multiply instruction finished, so the net execution time of the two instructions would be the sum of their individual execution times. The 6600 CPU had multiple functional units which could operate simultaneously, ''i.e.'', "in

parallel Parallel may refer to: Mathematics * Parallel (geometry), two lines in the Euclidean plane which never intersect * Parallel (operator), mathematical operation named after the composition of electrical resistance in parallel circuits Science a ...

", allowing the CPU to overlap instructions' execution times. For example, a 6600 CPU could begin executing an add instruction in the next CPU cycle following the beginning of a multiply instruction (assuming, of course, that the result of the multiply instruction was not an operand of the add instruction), so the net execution time of the two instructions would simply be the (longer) execution time of the multiply instruction. The 6600 CPU also had an ''instruction stack'', a kind of ''

instruction cache A CPU cache is a hardware cache used by the central processing unit (CPU) of a computer to reduce the average cost (time or energy) to access data from the main memory. A cache is a smaller, faster memory, located closer to a processor core, which ...

'', which helped increase CPU throughput by reducing the amount of CPU idle time caused by waiting for memory to respond to instruction fetch requests. The two kinds of CPUs were instruction compatible, so that a program that ran on either of the kinds of CPUs would run the same way on the other kind but would run faster on the 6600 CPU. Indeed, all models of the 6000 series were fully inter-compatible. The CDC 6400 had one CPU (a 6400 CPU), the CDC 6500 had two CPUs (both 6400 CPUs), the CDC 6600 had one CPU (a 6600 CPU), and the CDC 6700 had two CPUs (one 6600 CPU and one 6400 CPU).

Central Processor (CP)

The Central Processor (CP) and main memory of the 6400, 6500, and 6600 machines had a 60-bit word length. The Central Processor had eight general purpose 60-bit registers X0 through X7, eight 18-bit address registers A0 through A7, and eight 18-bit "increment" registers B0 through B7. B0 was held at zero permanently by the hardware. Many programmers found it useful to set B1 to 1, and similarly treat it as inviolate. The CP had no instructions for input and output, which are accomplished through Peripheral Processors (below). No opcodes were specifically dedicated to loading or storing memory; this occurred as a side effect of assignment to certain A registers. Setting A1 through A5 loaded the word at that address into X1 through X5 respectively; setting A6 or A7 stored a word from X6 or X7. No side effects were associated with A0. A separate hardware load/store unit, called the ''stunt box'', handled the actual data movement independently of the operation of the instruction stream, allowing other operations to complete while memory was being accessed, which required eight cycles, in the best case. The 6600 CP included ten parallel functional units, allowing multiple instructions to be worked on at the same time. Today, this is known as a

superscalar processor A superscalar processor (or multiple-issue processor) is a CPU that implements a form of parallelism called instruction-level parallelism within a single processor. In contrast to a scalar processor, which can execute at most one single ins ...

design, but it was unique for its time. Unlike most modern CPU designs, functional units were not pipelined; the functional unit would become busy when an instruction was "issued" to it and would remain busy for the entire time required to execute that instruction. (By contrast, the CDC 7600 introduced pipelining into its functional units.) In the best case, an instruction could be issued to a functional unit every 100 ns clock cycle. The system read and decoded instructions from memory as fast as possible, generally faster than they could be completed, and fed them off to the units for processing. The units were: * floating point multiply (two copies) * floating point divide * floating point add * "long" integer add * incrementers (two copies; performed memory load/store) * shift * Boolean logic * branch Floating-point operations were given pride of place in this

architecture Architecture is the art and technique of designing and building, as distinguished from the skills associated with construction. It is both the process and the product of sketching, conceiving, planning, designing, and construction, constructi ...

: the CDC 6600 (and kin) stand virtually alone in being able to execute a 60-bit

floating point In computing, floating-point arithmetic (FP) is arithmetic on subsets of real numbers formed by a ''significand'' (a signed sequence of a fixed number of digits in some base) multiplied by an integer power of that base. Numbers of this form ...

multiplication in time comparable to that for a program branch. A recent analysis by Mitch Alsup of James Thornton's book, "Design of a Computer", revealed that the 6600's Floating Point unit is a 2 stage pipelined design. Fixed point addition and subtraction of 60-bit numbers were handled in the Long Add Unit, using

for negative numbers. Fixed point multiply was done as a special case in the floating-point multiply unit—if the exponent was zero, the FP unit would do a single-precision 48-bit floating-point multiply and clear the high exponent part, resulting in a 48-bit integer result. Integer divide was performed by a macro, converting to and from floating point. Previously executed instructions were saved in an eight-word

cache Cache, caching, or caché may refer to: Science and technology * Cache (computing), a technique used in computer storage for easier data access * Cache (biology) or hoarding, a food storing behavior of animals * Cache (archaeology), artifacts p ...

, called the "stack". In-stack jumps were quicker than out-of-stack jumps because no memory fetch was required. The stack was flushed by an unconditional jump instruction, so unconditional jumps at the ends of loops were conventionally written as conditional jumps that would always succeed. The system used a 10

MHz The hertz (symbol: Hz) is the unit of frequency in the International System of Units (SI), often described as being equivalent to one event (or cycle) per second. The hertz is an SI derived unit whose formal expression in terms of SI base u ...

clock, with a four-phase signal. A floating-point multiplication took ten cycles, a division took 29, and the overall performance, taking into account memory delays and other issues, was about 3 MFLOPS. Using the best available compilers, late in the machine's history, FORTRAN programs could expect to maintain about 0.5 MFLOPS.

Memory organization

User programs are restricted to use only a contiguous area of main memory. The portion of memory to which an executing program has access is controlled by the ''RA'' (Relative Address) and ''FL'' (Field Length) registers which are not accessible to the user program. When a user program tries to read or write a word in central memory at address ''a'', the processor will first verify that a is between 0 and FL-1. If it is, the processor accesses the word in central memory at address RA+a. This process is known as base-bound relocation; each user program sees core memory as a contiguous block words with length FL, starting with address 0; in fact the program may be anywhere in the physical memory. Using this technique, each user program can be moved ("relocated") in main memory by the operating system, as long as the RA register reflects its position in memory. A user program which attempts to access memory outside the allowed range (that is, with an address which is not less than FL) will trigger an interrupt, and will be terminated by the operating system. When this happens, the operating system may create a

core dump In computing, a core dump, memory dump, crash dump, storage dump, system dump, or ABEND dump consists of the recorded state of the working Computer storage, memory of a computer program at a specific time, generally when the program has crash (com ...

which records the contents of the program's memory and registers in a file, allowing the developer of the program a means to know what happened. Note the distinction with

virtual memory In computing, virtual memory, or virtual storage, is a memory management technique that provides an "idealized abstraction of the storage resources that are actually available on a given machine" which "creates the illusion to users of a ver ...

systems; in this case, the entirety of a process's addressable space must be in core memory, must be contiguous, and its size cannot be larger than the real memory capacity. All but the first seven

machines could be configured with an optional Extended Core Storage (ECS) system. ECS was built from a different variety of core memory than was used in the central memory. This memory was slower, but cheap enough that it could be much larger. The primary reason was that ECS memory was wired with only two wires per core (contrast with five for central memory). Because it performed very wide transfers, its sequential transfer rate was the same as that of the small core memory. A 6000 CPU could directly perform block memory transfers between a user's program (or operating system) and the ECS unit. Wide data paths were used, so this was a very fast operation. Memory bounds were maintained in a similar manner as central memory, with an RA/FL mechanism maintained by the operating system. ECS could be used for a variety of purposes, including containing user data arrays that were too large for central memory, holding often-used files, swapping, and even as a communication path in a multi-mainframe complex.

Peripheral Processors (PPs)

To handle the "housekeeping" tasks, which in other designs were assigned to the CPU, Cray included ten other processors, based partly on his earlier computer, the CDC 160-A. These machines, called Peripheral Processors, or PPs, were full computers in their own right, but were tuned to performing I/O tasks and running the operating system. (Substantial parts of the operating system ran on the PP's; thus leaving most of the power of the Central Processor available for user programs.) Only the PPs had access to the I/O

channels Channel, channels, channeling, etc., may refer to: Geography * Channel (geography), a landform consisting of the outline (banks) of the path of a narrow body of water. Australia * Channel Country, region of outback Australia in Queensland and pa ...

. One of the PPs (PP0) was in overall control of the machine, including control of the program running on the main CPU, while the others would be dedicated to various I/O tasks; PP9 was dedicated to the system console. When the CP program needed to perform an operating system function, it would put a request in a known location (''Reference Address'' + 1) monitored by PP0. If necessary, PP0 would assign another PP to load any necessary code and to handle the request. The PP would then clear RA+1 to inform the CP program that the task was complete. The unique role of PP0 in controlling the machine was a potential single point of failure, in that a malfunction here could shut down the whole machine, even if the nine other PPs and the CPU were still functioning properly. Cray fixed this in the design of the successor 7600, when any of the PPs could be the controller, and the CPU could reassign any one to this role. Each PP included its own memory of 4096

12-bit Before the widespread adoption of ASCII in the late 1960s, six-bit character codes were common and a 12-bit word, which could hold two characters, was a convenient size. This also made it useful for storing a single decimal digit along with a si ...

words. This memory served for both for I/O buffering and program storage, but the execution units were shared by ten PPs, in a configuration called the Barrel and slot. This meant that the execution units (the "slot") would execute one instruction cycle from the first PP, then one instruction cycle from the second PP, etc. in a round robin fashion. This was done both to reduce costs, and because access to CP memory required 10 PP clock cycles: when a PP accesses CP memory, the data is available next time the PP receives its slot time.

Central Processor access

In addition to a conventional instruction set, the PPs have several instructions specifically intended to communicate with the central processor. * CRD d - transfers one 60-bit word from central memory at the address specified by the PPs ''A'' register to five consecutive PP words beginning at address ''d''. * CRM d,m - similar to CRD, but transfers a block of words whose length was previously stored at location ''d'' into PP memory starting at PP address ''m''. * CWD d - assembles five consecutive PP words beginning at location ''d'', and transfers them to the central memory location specified by register ''A''. * CWM d,m - transfers a block starting at PP memory address ''m'' to central memory. The central memory address was stored in register ''A'', and the length was stored at location ''d'' prior to execution. * RPN - transfers the contents of the central processor's program address register to the PP's ''A'' register. * EXN - ''Exchange Jump'' transmits an address from the ''A'' register and tells the processor to perform an ''Exchange Jump'' using the address specified. The CP Exchange Jump interrupts the processor, loads its registers from the specified location and stores the previous contents at the same location. This performs a task switch.

Wordlengths, characters

The central processor has 60-bit words, while the peripheral processors have

words. CDC used the term "byte" to refer to 12-bit entities used by peripheral processors; characters are 6-bit, and central processor instructions are either 15 bits, or 30 bits with a signed 18-bit address field, the latter allowing for a directly addressable memory space of 128K words of central memory (converted to modern terms, with 8-bit bytes, this just under 1 MB). The signed nature of the address registers limits an individual program to 128K words. (Later CDC 6000-compatible machines could have 256K or more words of central memory, budget permitting, but individual user programs were still limited to 128K words of CM.) Central processor instructions start on a word boundary when they are the target of a jump statement or subroutine return jump instruction, so no-op instructions are sometimes required to fill out the last 15, 30 or 45 bits of a word. Experienced assembler programmers could fine-tune their programs by filling these ''no-op'' spaces with misc instructions that would be needed later in the program. The 6-bit characters, in an encoding called

CDC display code Display code is the six-bit character code used by many computer systems manufactured by Control Data Corporation, notably the CDC 6000 series in 1964, the 7600 in 1967 and the following Cyber series in 1971. The CDC 6000 series and their succes ...

, could be used to store up to 10 characters in a word. They permitted a character set of 64 characters, which is enough for all upper case letters, digits, and some punctuation. It was certainly enough to write FORTRAN, or print financial or scientific reports. There were actually two variations of the CDC display code character sets in use — 64-character and 63-character. The 64-character set had the disadvantage that the ":" (colon) character would be ignored (interpreted as zero fill) if it were the last character in a word. A complementary variant, called 6/12 display code, was also used in the Kronos and NOS timesharing systems to allow full use of the

ASCII ASCII ( ), an acronym for American Standard Code for Information Interchange, is a character encoding standard for representing a particular set of 95 (English language focused) printable character, printable and 33 control character, control c ...

character set in a manner somewhat compatible with older software. With no byte addressing instructions at all, code had to be written to pack and shift characters into words. The very large words, and comparatively small amount of memory, meant that programmers would frequently economize on memory by packing data into words at the bit level. Due to the large word size, and with 10 characters per word, it was often faster to process a word's worth of characters at a time, rather than unpacking/processing/repacking them. For example, the CDC

COBOL COBOL (; an acronym for "common business-oriented language") is a compiled English-like computer programming language designed for business use. It is an imperative, procedural, and, since 2002, object-oriented language. COBOL is primarily ...

compiler was actually quite good at processing decimal fields using this technique. These sorts of techniques are now commonly used in the "multi-media" instructions of current processors.

Physical design

The machine was built in a plus-sign-shaped cabinet with a pump and heat exchanger in the outermost of each of the four arms. Cooling was done with

Freon Freon ( ) is a registered trademark of the Chemours Company and generic descriptor for a number of halocarbon products. They are stable, nonflammable, low toxicity gases or liquids which have generally been used as refrigerants and as aerosol p ...

circulating within the machine and exchanging heat to an external chilled water supply. Each arm could hold four chassis, each about thick, hinged near the center, and opening a bit like a book. The intersection of the "plus" was filled with cables that interconnected the chassis. The chassis were numbered from 1 (containing all 10 PPUs and their memories, as well as the 12 rather minimal I/O channels) to 16. The main memory for the CPU was spread over many of the chassis. In a system with only 64K words of main memory, one of the arms of the "plus" was omitted. The logic of the machine was packaged into modules about square and about thick. Each module had a connector (30 pins, two vertical rows of 15) on one edge, and six test points on the opposite edge. The module was placed between two aluminum cold plates to remove heat. The module consisted of two parallel printed circuit boards, with components mounted either on one of the boards or between the two boards. This provided a very dense package; generally impossible to repair, but with good heat transfer characteristics. It was known as cordwood construction.

Operating system and programming

There was a sore point with the 6600

operating system An operating system (OS) is system software that manages computer hardware and software resources, and provides common daemon (computing), services for computer programs. Time-sharing operating systems scheduler (computing), schedule tasks for ...

support — slipping timelines. The machines originally ran a very simple job-control system known as COS ( Chippewa Operating System), which was quickly "thrown together" based on the earlier

CDC 3000 The CDC 3000 series ("thirty-six hundred" or "thirty-one hundred") are a family of mainframe computers from Control Data Corporation (CDC). The first member, the CDC 3600, was a 48-bit system introduced in 1963. The same basic design led to the c ...

operating system in order to have something running to test the systems for delivery. However the machines were intended to be delivered with a much more powerful system known as SIPROS (for Simultaneous Processing Operating System), which was being developed at the company's System Sciences Division in

Los Angeles Los Angeles, often referred to by its initials L.A., is the List of municipalities in California, most populous city in the U.S. state of California, and the commercial, Financial District, Los Angeles, financial, and Culture of Los Angeles, ...

. Customers were impressed with SIPROS' feature list, and many had SIPROS written into their delivery contracts. SIPROS turned out to be a major fiasco. Development timelines continued to slip, costing CDC major amounts of profit in the form of delivery delay penalties. After several months of waiting with the machines ready to be shipped, the project was eventually cancelled. The programmers who had worked on COS had little faith in SIPROS and had continued working on improving COS. Operating system development then split into two camps. The CDC-sanctioned evolution of COS was undertaken at the

Sunnyvale, California Sunnyvale () is a city located in the Santa Clara Valley in northwestern Santa Clara County, California, United States. Sunnyvale lies along the historic El Camino Real (California), El Camino Real and U.S. Route 101 in California, Highway 1 ...

software development laboratory. Many customers eventually took delivery of their systems with this software, then known as SCOPE (Supervisory Control Of Program Execution). SCOPE version 1 was, essentially, dis-assembled COS; SCOPE version 2 included new device and file system support; SCOPE version 3 included permanent file support, EI/200 remote batch support, and INTERCOM

time-sharing In computing, time-sharing is the Concurrency (computer science), concurrent sharing of a computing resource among many tasks or users by giving each Process (computing), task or User (computing), user a small slice of CPU time, processing time. ...

support. SCOPE always had significant reliability and maintainability issues. CDC 6000 series SCOPE 3

The underground evolution of COS took place at the

Arden Hills, Minnesota Arden Hills ( ) is a city in Ramsey County, Minnesota, United States. The population was 9,939 at the 2020 census. Bethel University and its seminary is located in the city. Also, the campus of University of Northwestern – St. Paul straddl ...

assembly plant. MACE ( regMansfield And

ave is a Latin word, used by the Roman Empire, Romans as a salutation (greeting), salutation and greeting, meaning 'wikt:hail, hail'. It is the singular imperative mood, imperative form of the verb , which meant 'Well-being, to be well'; thus on ...

Cahlander Executive) was written largely by a single programmer in the off-hours when machines were available. Its feature set was essentially the same as COS and SCOPE 1. It retained the earlier COS file system, but made significant advances in code modularity to improve system reliability and adaptiveness to new storage devices. MACE was never an official product, although many customers were able to wrangle a copy from CDC. The unofficial MACE software was later chosen over the official SCOPE product as the basis of the next CDC operating system, Kronos, named after the Greek god of time. The main marketing reason for its adoption was the development of its TELEX time-sharing feature and its BATCHIO remote batch feature. Kronos continued to use the COS/SCOPE 1 file system with the addition of a permanent file feature. An attempt to unify the SCOPE and Kronos operating system products produced NOS, (Network Operating System). NOS was intended to be the sole operating system for all CDC machines, a fact CDC promoted heavily. Many SCOPE customers remained software-dependent on the SCOPE architecture, so CDC simply renamed it NOS/BE (Batch Environment), and were able to claim that everyone was thus running NOS. In practice, it was far easier to modify the Kronos code base to add SCOPE features than the reverse. The assembly plant environment also produced other operating systems which were never intended for customer use. These included the engineering tools SMM for hardware testing, and KALEIDOSCOPE, for software smoke testing. Another commonly used tool for CDC Field Engineers during testing was MALET (Maintenance Application Language for Equipment Testing), which was used to stress test components and devices after repairs or servicing by engineers. Testing conditions often used hard disk packs and magnetic tapes which were deliberately marked with errors to determine if the errors would be detected by MALET and the engineer. The names SCOPE and COMPASS were used by CDC for both the

, including the 6600, and the

: * The name

COMPASS A compass is a device that shows the cardinal directions used for navigation and geographic orientation. It commonly consists of a magnetized needle or other element, such as a compass card or compass rose, which can pivot to align itself with No ...

was used by CDC for the

Assembly language In computing, assembly language (alternatively assembler language or symbolic machine code), often referred to simply as assembly and commonly abbreviated as ASM or asm, is any low-level programming language with a very strong correspondence bet ...

s on both families. * The name SCOPE was used for its implementations on the 3000 and 6000 series."CDC delivered an early version of their SCOPE operating system for the 3600"

CDC 7600

The

was originally intended to be fully compatible with the existing 6000-series machines as well; it started life known as the CDC 6800. But during its design, the designers determined that maintaining complete compatibility with the existing 6000-series machines would limit how much performance improvement they could attain and decided to sacrifice compatibility for performance. While the CDC 7600's CPU was basically instruction compatible with the 6400 and 6600 CPUs, allowing code portability at the

high-level language A high-level programming language is a programming language with strong abstraction from the details of the computer. In contrast to low-level programming languages, it may use natural language ''elements'', be easier to use, or may automate (or ...

source code level, the CDC 7600's hardware, especially that of its Peripheral Processor Units (PPUs), was quite different, and the CDC 7600 required a different operating system. This turned out to be somewhat serendipitous because it allowed the designers to improve on some of the characteristics of the 6000-series design, such as the latter's complete dependence on Peripheral Processors (PPs), particularly the first (called PP0), to control operation of the entire computer system, including the CPU(s). Unlike the 6600 CPU, the CDC 7600's CPU could control its own operation via a Central Exchange jump (XJ) instruction that swapped all register contents with core memory. In fact, the 6000-series machines were

retrofitted Retrofitting is the addition of new technology or features to older systems. Retrofits can happen for a number of reasons, for example with big capital expenditures like naval vessels, military equipment or manufacturing plants, businesses or go ...

with this capability.

References

External links

Neil R. Lincoln with 18 Control Data Corporation (CDC) engineers on computer architecture and design

Charles Babbage Institute The IT History Society (ITHS) is an organization that supports the history and scholarship of information technology by encouraging, fostering, and facilitating archival and historical research. Formerly known as the Charles Babbage Foundation, ...

, 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 6600,

CDC 8600 The CDC 8600 was the last of Seymour Cray's supercomputer designs while he worked for Control Data Corporation. As 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 fast ...

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

and

Seymour Cray Seymour Roger Cray (September 28, 1925 – October 5, 1996)
– was an American

Parallel operation in the Control Data 6600, James Thornton

– by C.

Gordon Bell Chester Gordon Bell (August 19, 1934 – May 17, 2024) was an American electrical engineer and manager. An early employee of Digital Equipment Corporation (DEC), from 1960–1966, Bell designed several of their PDP machines and later served as ...

of Microsoft Research (formerly of DEC) * – overview with pictures {{Authority control 6600 Supercomputers Transistorized computers Computer-related introductions in 1964 60-bit computers

History and impact

Description

Peripheral processors

Instruction-set architecture of CP

Models

Central Processor (CP)

Memory organization

Peripheral Processors (PPs)

Central Processor access

Wordlengths, characters

Physical design

Operating system and programming

CDC 7600

See also

References

Further reading

External links