After Computing Devices became affiliated with the Bendix Corporation, the company became the Canadian representative for Bendix equipment. The 102-D in their Ottawa offices was replaced with a Bendix G-15D. Another G-15D was soon installed in the Department of Electrical Engineering at the University of Manitoba. I can't recall how many G-15Ds were sold in Canada, but I can remember visiting the University of Guelph where Gordon Ashton was using one for statistical calculations. At one time the company installed a G15-D in a van which was used for giving demonstrations in various parts of Western Canada.
There were apparently several models of the Bendix G-15 computer, designated by a suffix "A", "C" and "D", and they were roughly comparable. The basic system was contained in a cabinet 32 inches by 27 inches by 61 inches and weighing 650 pounds. There was a control panel on the front of the cabinet and also a paper tape reader which accommodated a removable tape magazine. A Flexowriter was used for manual input and for low-speed paper tape input and output. Neither a separate power supply nor air conditioning was required. The cost of the basic system was about $45,000. Optional equipment included a card reader and punch, magnetic tape, graph plotter, and a digital differential analyzer. The accompanying photograph shows the G15-D at Computing Devices. The person seated at the card punch is Peggy Steen whom we shall mention later in the discusion of programming. The clipbord shown on the table in the lower left probably contains the booking schedule for use of the G-15D.
The magnetic drum memory consisted of 2160 29-bit words. Internal operation was binary with single-, double- and arbitrary-precision arithmetic. Addition times were about 15 milliseconds including access, and multiplication and division times were approximately 32 milliseconds. A two-address instruction was used where the first address specified the operation and the second the address of the next command. There were fifty basic commands which were considered, according to one of the G15 manuals, "sufficient to program any problem", and which could be modified to give about 1300 different commands which would permit an increase in efficiency and speed of computation. Machine-language programming required considerable skill and patience as occasionally a single coding error could take a day or more to locate and correct.
In addition to machine-language programming there was an interpretive system called "Intercom" and a compiler called "Pogo". In 1960 an "Algo" compiler based on the Algol language was introduced; it will be discussed in a later section. Intercom 1000 Single-Precision had a capacity of 1200 five-digit words while Intercom 1000 Double-Precision allowed up to 1000 twelve-digit words. There was a total of about 50 one-address commands with the format "Op Addr" for floating-point arithmetic, transfer of control, input-output, and the use of index registers as well as number of arithmetic and input-output subroutines. The Intercom 1000 system provided a great simplication over the very complicated machine-language programming for the G15. I can still remember Peggy Steen, working from a carefully prepared flow diagram that was provided her, coding in her very neat handwriting page after page of almost error-free Intercom commands.
The present simulation of Intercom for the sample problem required implementing the following nine commands, where "A" refers as usual to the Accumulator:
41 Subtract: A <- (A) - (Addr)
42 Clear and Add: A <- (Addr)
43 Add: A <- (A) + (Addr)
49 Store: Addr <- (A)
20 Trans. if (A) >= 0: If (A) >= 0, take next instruction from Addr
23 Trans. if (A) = 0: If (A) = 0, take next instruction from Addr
29 Trans.: Take next instruction from Addr
33 Print: Type fixed point number and tab
55 Read: Read from paper tape into the channel specified by the first two digits
of Addr and word positions 00, 01, ... . For example, "55 0803" will read
three numbers into 0800, 0801 and 0802.
The J script file is given in G15.ijs, and the program for the sample problem is given below.
0700 42 0722 A <- 0 0701 49 0725 N <- 0 0702 49 0726 Sum <- 0 0703 49 0727 Max <- 0 0704 55 0801 Read P 0705 42 0800 A <- P 0706 23 0718 Is P = 0? 0707 43 0726 Sum <- Sum + P 0708 49 0726 0709 42 0725 N <- N +1 0710 43 0723 0711 49 0725 0712 42 0727 A <- Max 0713 41 0800 Max - P 0714 20 0704 Is Max - P >= 0? 0715 42 0800 Max <- P 0716 49 0727 0717 29 0704 Trans. to 0704 0718 33 0725 Print N 0719 33 0726 Print Sum 0720 33 0727 Print Max 0721 67 0000 Halt 0722 0 0723 1 0724 Working storage 0725 0726 0727
|Bendix G15D Intercom|
Information about the G-15 may be found at the websites of Paul Pierce of Portland, Oregon and the Australia Computer Museum.