IBM Advanced Computing Systems -- Technical Description sections

Mark Smotherman
last updated January 2, 2017

I built a Precursor that ran at a 10ns cycle. 5 levels of logic. Each chip could dissipate 3 watts and with 625 chips we had to have coolant. We used FC78 as a liquid coolant. The precursor was a path through a 24 bit adder.

-- Bill Mooney, personal correspondence, describing a test of ACS circuitry in 1968

Explanatory sidebars


Chips and Packaging


In a 1968 paper, Richard Chu and colleagues published a chart that compared junction temperatures for a hypothetical array of components based on air and various forms of liquid cooling. [Richard Chu, Martin Cohen, and John Seely, "Thermal considerations and techniques for electronic circuit packages in modern digital computers," Proc. 9th Intl. Electronic Circuit Packaging Symposium, 1968, session 5/3, pp. 1-9.] FC-78 and FC-88 are fluorocarbon products made by the 3M company. (Freon is a widely-recognized tradename for similar products made by Dupont.) PC is component power.

junction temperature chart

It was clear that chips with power dissipation in the range contemplated by ACS would need extensive cooling, and thus there were several types of cooling assemblies and modules developed as part of the ACS project.

Sidebar - Chip terminology

The word "chip" can refer to the unmounted square or rectangular piece of silicon cut from a manufactured silicon wafer. This small piece of silicon is also called an integrated circuit die. Alternatively, the word "chip" can refer to a mounted die in one of various types of ceramic, metal, and/or plastic packages, e.g., a Dual Inline Package (DIP), a pin grid array (PGA), etc. The meaning of "chip" is usually clear from the context. The part of the package in direct contact with the die is sometimes called the chip carrier, header, or pad.

A single die may be mounted in a package, or there may be multiple dies per package. The package in the latter instance is sometimes called a multi-chip module (MCM). If the packages are mounted on a printed circuit board (PCB), the combination of packages and board may be referred to simply as a card or board (depending on size). A small board with multiple packages that may itself be subsequently mounted to a larger board or placed in some type of enclosure is sometimes called a multi-chip carrier (MCC) or sometimes a multi-chip module (MCM). A combination of multiple packages, boards, and/or enclosures may be referred to as a module or assembly.

Sidebar - Circuit counts rather than transistor counts

Even though we typically use transistor count as the preferred metric of chip complexity today, circuit count was the common metric in the 1960s. A "circuit" was considered to be a logic gate or flip-flop, and thus a circuit represented multiple components such as transistors, resistors, and diodes. In 1967, Motorola authors Jan Narud, Curtis Phillips, and Walter Seelbach, gave the following definitions in their paper, "Complex monolithic arrays: Some aspects of design and fabrication," Proc. 6th Symposium on Adaptive Processes, 1967, pp. 303-308:

For ECL gates, they use a count of eight components per gate. So, for the circuit counts used on this page, you can multiply by five and have an approximate transistor count equivalent.

Sidebar - Logic families (as of mid-1960s, prior to CMOS dominance)

(See R. Henle and L. Hill, "Integrated computer circuits - past, present, and future," Proceedings of the IEEE, vol. 54, no. 12, December 1966, pp. 1849-1860.)

Sidebar - IBM mainframe packaging families (in chronological order, with approx. complexity)

Sidebar - Technology and performance comparison of various high-performance machines

Machine Delivered CPU
Packaging Cooling Schildberger
Index 2
Index 3
CDC 1604 1960 - 6400 ns air 20 58
IBM Stretch 1961 300 ns - 2180 ns CSL SMS oil-immersed
core memory
631 372
IBM 7094 1962 2000 ns - 2000 ns CSL SMS air 96 176
IBM 7094-II 1964 1400 ns - 2000 ns CSL SMS air 95 217
CDC 3600 1963 1400 ns - air 75 316
CDC 6600 1964 100 ns - 1000 ns DCTL "cordwood"4 CFC 5 4090 7020 2.09 0.48
IBM S/360 M65 1965 200 ns - 750 ns DTL SLT air 0.7 810 1390 0.521
IBM S/360 M75 1966 195 ns - 750 ns DTL SLT air 0.89
IBM S/360 M91 1967 60 ns - 780 ns CSEF ASLT (ACPX) water 6 5.0
CDC 7600 1969 27.5 ns - 275 ns DCTL 8-board
CFC 7 10.3 3.3
IBM S/360 M85 1969 80 ns 80-160 ns 960 ns CSEF MST-4 water 1.92 - 2.4
ACS cancelled
in 1969
10 ns
50 nsec 300 nsec ECL MSI package immersion
in CFC
IBM S/370 M165 1971 80 ns 80-160 ns 2000 ns CSEF MST-4 water 1.6 - 2.0 3515 2.21 0.77
IBM S/360 M195 1971 54 ns 54-162 ns 756 ns CSEF MST 4 water 5.00 2.5
IBM S/370 M168 1973 80 ns 80-160 ns 320 ns CSEF MST (1,2,4,A) water 2.36 - 2.74 2.44 1.2
CDC 8600 cancelled
in 1974
8 ns
- 256 ns 9 ECL 18-board
Amdahl 470 V/6 1975 10 32.5 ns 65 ns 200 ns ECL LSI package11 air 12 4.4 13 4.64 1.1
Cray-1 1976 12.5 ns - 50 ns ECL ceramic
CFC 14 160 16.2 15 3.4 16
IBM 3033 17 1978 57 ns 57-114 ns 285 ns CSEF MST (1,2,4,
water 4.9 - 9 19019 5.68 1.7
IBM 3081 1981 26 ns 26-52 ns 312 ns TTL TCM water 10.2 - 15.4 6.58 - 8.2 2.0

1 I chose not to use John McCallum's normalized MIPS numbers since his amalgamation of different sources ends up with the M65 rated faster than the M75.
2 values from line 14 of Tables II.2.11.1 and II.2.11.1a in M. Phister, Jr., Data Processing Technology and Economics, 2nd ed., 1979
3 values from line 13 of Table II.2.11.1 in Phister, op. cit.
4 James Thornton describes a 6600 cordwood module as having two small printed circuit boards with components mounted on and between the boards; each module has up to 64 transistors and implements 30 or more gates
5 see US Patent 3,334,684, Rousch and Mazorol, "Cooling system for data processing equipment," 1967
6 see the overview of IBM cooling methods in Chu, op. cit. The Model 91 cooling was patented as US Patent 3,317,798, Chu, et al., "Cooling electrical apparatus," 1967
7 see US Patents 3,865,183, Rousch, "Cooling systems for electronic modules," 1975 (and 3,904,933, Davis, 1975)
8 note that an ACS precursor ran at 10 ns (100 MHz) in 1968; 1967-68 presentations of the ACS-1 quoted 12.5 ns (80 MHz)
9 reflects latency estimate for 8600 core memory design ca. 1972; a later decision was made to redesign the memory modules using semiconductor memory
10 according to Robert Doran, a non-virtual-memory 470 would have shipped in 1973 but was preempted by the S/370 M158 and M168 announcements in 1972; see the 1973 Amdahl 470/6 System Machine Reference Manual
11 see R. Beall, "Packaging for a super computer," Proc. IEEE Intercon, March 1974, pp. 1-9; see also US Patent 3,808,475, Buelow and Zasio, "LSI chip construction and method," 1974 (and 3,981,070, 1976); US Patent 4,016,463, Beall, Buelow, and Zasio, "High density multilayer printed circuit card assembly and method," 1977; US Patent 4,115,837, Beall and Zasio, "LSI chip package and method," 1978 (and 4,396,971, 1983)
12 see Beall, op. cit.; see also US Patent 3,903,404, Beall, Buelow, and Zasio, "Computer construction and method," 1975
13 number for V/6 model II, which had a larger cache
14 see US Patent 4,120,021, Rousch, "Cooling system for electronic assembly," 1978
15 scalar mode; 98.0 in vector mode on Cray-1S
16 a Cray-1S ran at 12 MFLOPS on Linpack in 1983, which was increased later to 27 MFLOPS
17 note that the 3033 was based on the 85/165/168 microarchitecture since IBM was busy working on Future System (FS) between 1971-1975; see US Patent 4,200,927, Hughes, et al., "Multi-instruction stream branch processing mechanism," 1980

sidebar: Comparison of CDC, IBM, and Amdahl circuit packaging

CDC, IBM, and Amdahl circuit modules

Back row: circuit card similar to what was used in earlier CDC computers, cordwood module similar to what was used in CDC 6000 series, and eight-board module similar to what was used in the CDC 7600 (the particular module shown likely came from a later Cyber 175).
Front row: SMS circuit card similar to what was used in the IBM 7000 series, SLT card similar to what was used in the IBM S/360 series (other than the 91), IBM ACS chip package, and Amdahl 470 chip package mounted on a test card.

sidebar: Comparison of ACS board and Amdahl 470 board

ACS 1968-era circuit board with 10x10 array of chip packages next to 1975-era Amdahl 470 circuit board. (The ACS chip packages are empty and are not soldered to the board; the ACS board could hold up to 620 chip packages.)

close up of cooling stud
close up of cooling stud

ACS chip package compared to Amdahl 470 chip package. (The ACS chip package is capped but not soldered to the test card.)

test cards
close up of cooling stud
close up of cooling stud

Acknowledgements: Thanks to Bill Mooney for the gift of the ACS chips and the thermal module. Thanks to Lynn Conway for suggesting that definitions should be given for chip terminology and circuit counts. Thanks to my daughter, Sara, for taking many of the pictures of the chips and thermal module, and to Dr. Andy Mount of Clemson for taking the macro pcitures.

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