Eniac performs multiplication by a built-in table of the products in the 10-by-10 multiplication table, using the method of _left-hand components_ and _right-hand components_ (see Supplement 2). For example, suppose that the 3rd digit of the multiplier is 7 and that the 5th digit of the multiplicand is 6. Then, when Eniac attends to the 3rd digit of the multiplier, the right-hand digit of the 42 = 6 × 7 is gathered in one accumulator, and the left-hand digit 4 is gathered in another accumulator. After Eniac has attended to all the digits of the multiplier, then Eniac performs one more addition and transfers the sum of the left-hand digits into the right-hand digits accumulator. Eniac does division in rather a novel way. First, the divisor is subtracted over and over until the result becomes negative or 0. Then the machine shifts to the next column and adds the divisor until the result becomes positive or 0. It continues this process, alternating from column to column. For example, suppose that we divide 3 into 84 in this way. We have: ______ _ 3 ) 84 ( 32 -3 —— +54 -3 —— +24 -3 —— -6 +3 —— -3 +3 —— 0 After we subtract 3 the third time, the result becomes negative,-6; in the next column, after we add 3 twice, the result becomes 0. The quotient is _ 32, which is the same as 30 - 2, or 28; and 3 × 28 is 84. Thus the process checks. Consulting a Table Eniac has three Function Tables. Here you can store numbers or instructions for the machine to refer to. Each Function Table has 104 _arguments_ (see Supplement 2). For each argument, you can store 12 digits and 2 signs that may be plus or minus. This capacity can be devoted to one 12-digit number with a sign, or to two 6-digit numbers each with a sign, or to six 2-digit instructions. The three Function Tables are panels 43, 44, and 45. To put in the numbers or instructions, you have to go over to these panels and set the numbers or instructions, digit by digit, turning dial switches by hand. It is slow and hard to do this right, but once it is done, Eniac can refer to any number or instruction in any table in ¹/₁₀₀₀ of a second. This is much faster than the table reference time in any other of the giant brains built up to 1948. Programming We said above that Eniac has over 100 control lines or program trunks along which instructions can be sent. These instructions are expressed as pulses called _program pulses_. Now how do we make these pulses do what we want them to do? For example, how can we instruct Accumulator 11 to add what it holds into Accumulator 13?