“位”的来历

ENIAC /ˈiniæk/ or /ˈeniæk/ Electronic Numerical Integrator And Computer.

EDVAC (Electronic Discrete Variable Automatic Computer) was one of the earliest electronic computers. Unlike its predecessor the ENIAC, it was binary rather than decimal, and was designed to be a stored-program computer.

The First Draft of a Report on the EDVAC (commonly shortened to First Draft) is an incomplete 101-page document written by John von Neumann and distributed on June 30, 1945 by Herman Goldstine, security officer on the classified ENIAC project. It contains the first published description of the logical design of a computer using the stored-program concept, which has controversially come to be known as the von Neumann architecture.

Von Neumann wrote the report by hand while commuting by train to Los Alamos, New Mexico and mailed the handwritten notes back to Philadelphia. Goldstine had the report typed and duplicated.

Von Neumann describes a detailed design of a "very high speed automatic digital computing system." He divides it into six major subdivisions: a central arithmetic part, CA, a central control part, CC, memory, M, input, I, output, O, and (slow) external memory, R, such as punched cards, Teletype tape, or magnetic wire or steel tape.

The CA will perform addition, subtraction, multiplication, division and square root. Other mathematical operations, such as logarithms and trigonometric functions are to be done with table look up and interpolation, possibly biquadratic. He notes that multiplication and division could be done with logarithm tables, but to keep the tables small enough, interpolation would be needed and this in turn requires multiplication, though perhaps with less precision.

Numbers are to be represented in binary notation. He estimates 27 binary digits (he did not use the term "bit," which was coined by Claude Shannon in 1948) would be sufficient (yielding 8 decimal place accuracy) but rounds up to 30-bit numbers with a sign bit and a bit to distinguish numbers from orders, resulting in 32-bit word he calls a minor cycle. Two's complement arithmetic is to be used, simplifying subtraction. For multiplication and division, he proposes placing the binary point after sign bit, which means all numbers are treated as being between −1 and +1 and therefore computation problems must be scaled accordingly.

Vacuum tubes are to be used rather than relays [继电器] due to tubes’ ability operate in one microsecond vs. 10 milliseconds for relays.

A key design concept enunciated, and later named the Von Neumann architecture, is a uniform memory containing both numbers (data) and orders (instructions).

Von Neumann estimates the amount of memory required based on several classes of mathematical problems, including ordinary and partial differential equations, sorting and probability experiments. Of these, partial differential equations in two dimensions plus time will require the most memory, with three dimensions plus time being beyond what can be done using technology that was then available. He concludes that memory will be the largest subdivision of the system and he proposes 8,192 minor cycles (words) of 32-bits as a design goal, with 2,048 minor cycles still being useful. He estimates a few hundred minor cycles will suffice for storing the program.

In Sec 14.1 von Neumann proposes the format for orders, which he calls a code. Order types include the basic arithmetic operations, moving minor cycles between CA and M (word load and store in modern terms), an order (s) that selects one of two numbers based on the sign of the previous operation, input and output and transferring CC to a memory location elsewhere (a jump).

六级/考研单词: electron, numerical, compute, invariable, successor, decimal, prolong, classify, logic, controversy, commute, duplicate, digit, arithmetic, punch, subtract, mathematics, suffice, yield, complement, thereby, accordingly, vacuum, relay, data, instruct, dimension