Description of the IBM 704
1. Double Arithmetic Speed in Multiplication and
The Type 704 executes multiplication and division commands at double the speed of the present Type 701. The Type 701 performs the operations of multiplication or division in 456 microseconds, or approximately 2000 operations per second. The Type 704 multiplies or divides in 240 microseconds, or approximately 4000 operations per second. The doubling of speed in arithmetic, plus the use of index commands, more than doubles the effectiveness of the present Type 701.
2. Automatic Floating-Point Operation
The Type 704 is the first large-scale commercially available computer to employ fully automatic floating-point arithmetic commands. These commands enable the machine to record automatically and keep track of the size of all numbers during thousands of computing steps. At each step the most significant digits of any given number are always used in performing arithmetic. This ability is of tremendous importance in long sequential calculations which might typically involve millions of steps with numbers and their combined results varying from extremely small to unusually large numbers on any given step. Heretofore, this has been done by interpretive programs such as the IBM 701 SpeedCoding System.
The execution times for the various floating-point
a. Floating-Point Addition—84 microseconds*, or 11,000 per second.
b. Floating-Point Subtractions—84 microseconds*, or 11,000 per second.
c. Floating-Point Multiplication—204 microseconds, or 4,500 per second.
d. Floating-Point Division—216 microseconds, or 4,500 per second.
*In case the operands differ by 10 or less and normalization does not require more than 4 shifts.
This means floating-point addition can be accomplished in approximately 1/20 of the time and multiplication can be performed in approximately 1/7 of the time presently required on the Type 701.
3. Index Registers
Three special electronic registers have been added to the machine to facilitate the writing of programs. In normal practice many programs involve the repeated application of the same sequence of steps to data located in different parts of the memory. This requires writing programs to shift the sequence of steps so as to operate on the proper data at the proper time. Such manipulation of programs is done automatically in the Type 704 by reference to index registers which control the repeated application of a programmed routine. These registers increase the logical ability of the machine and, at the same time, provide for a reduction in the number of instructions now needed to perform the proper shifting and manipulation of a given sequence.
4. High-Speed Drum Switching and Transmission
Changes in switching techniques and equipment have been made on the Type 731 Magnetic Drum unit to provide more than a twelve fold speed increase in the transfer rate between magnetic drum and electrostatic storage. In the present Type 701 the magnetic drum is read at a rate of 800 words per second or the equivalent of 8000 digits per second. The Type 704 will read at 10,000 words per second or at the rate of 100,000 decimal digits per second. In addition to this, the initial access time has been reduced from an average of 50 milliseconds to an average of 12 milliseconds.
The addition of new commands enables the Type 704 to use the drum most effectively in table lookup operations. It is possible to consult tables stored on the drums without the necessity of bringing into the main memory any portion of the table other than that desired. The use of such high-speed table lockups is invaluable in many engineering and scientific applications.
5. New Logical Operations
The Type 701 has a total of 32 operations available to the programmer. In the Type 704 this number has been increased to 73. Among these new commands are:
a. Logical Multiplication to Accumulator.
b. Logical Multiplication to Memory.
c. Logical Addition to the Accumulator.
d. Logical Addition to the Memory.
These commands facilitate the extraction and combination of small pieces of information within the main memory . With such commands it is possible to perform processing and arithmetic efficiently on fields smaller or larger than 10 digits.
Another command, END AROUND CARRY ADD, has been added which will simplify the handling of the methods used in checking the flow of information among the various input/output units and the main memory. This will increase the overall checking ability to the machine with a simultaneous reduction in programming requirements.
Many additional transfer and test commands have
been added to increase the logical power and flexibility of the machine, as
well as to reduce the memory positions necessary to effect a given
program." [Annals of the History of Computing, Vol.5
Personal Reflections - Roger Mills:
One of the first operating systems developed for the IBM 704
was developed at North American Aviation (NAA). IBM developed a card-to-tape
reader and a tape-to-printer output unit. NAA developed programs to batch
cards for input from tape and to batch output on tape for printing. The
computing groups from NAA, Rand, and Lockheed combined to generate various areas
of computing for the IBM 704.