138 Part 2 The instruction-set processor: main-line computers

pared to the response times of real systems. Even with a drum there is considerable loss of computing and programming efficiency due to shuffling information back and forth between drum and computer.

WWI is designed for 2,048 registers of storage. Until recently there has been available only about 300 registers. This number, while small, has been adequate for much useful work. Very recently a second bank of new-model storage tubes has been added. These new tubes operate at 1,024 spots per tube bringing the total WWI storage to 1,280 registers. These tubes have been in the computer and under test for 2 months and in active use for about 2 weeks. In the next few months the tubes in the first bank will be replaced by new-model storage tubes bringing the total storage to 2,048. This number is on the lower end of what the project considers desirable. What the computer business needs, has needed, and will probably always need is a bigger, better, and faster storage device.

In a system where much valuable property and perhaps many human lives are dependent on the proper operation of the computing equipment, failures must be very rare. Furthermore, checking alone, however complete, is inadequate. It is not enough merely to know that the equipment has made an error. It is very unlikely that a man, presumably not too well suited to the work during normal conditions, can handle the situation in an emergency. Multiple machines with majority rule seem to be the best answer. Self-correcting machines are a possibility but appear to be too complicated to compete, especially as they provide no standby protection.

The characteristics of the Whirlwind I computer may be recapitulated as follows:

There are 32 possible operations, of which about 27 are assigned. They are of the usual types: addition, subtraction, multiplication, division, shifting by an arbitrary number of columns, transfer of all or parts of words, subprogram, and conditional subprogram. There are terminal equipment control orders and there are some special orders for facilitating double-length and floating-point operations.

One way to increase the effective speed of a machine is to provide built-in facilities for operations that occur frequently in the problems of interest. An example is an automatic co-ordinate transformation order. The addition of such facilities does not affect the general-purpose nature of the machine. The machine retains its old flexibility but becomes faster and more suited to a certain class of problems.

From March 14, 1951, at which time we began to keep detailed records, until November 22, 1951 a total of 950 hours of computer time were scheduled for applications use. The machine has been running on two shifts or a total of about 3,000 hours during this interval. The two-thirds time not used for applications has been used for machine improvement, adding equipment, and preventive maintenance.

Of the 950 hours available, 500 have been used by the scientific and engineering calculation group, the rest for control studies. The limited storage available until recently has been admittedly a serious handicap to the scientific and engineering applications people. There has not been room in storage for the lengthy subroutines necessary for convenient use of the machine. The largest part of their time has been spent in training, in setting up procedures, and in preparing a library of subroutines.

A partial list of the actual problems carried out by the group includes: