Серия IBM 1400: Бизнес-компьютеры с десятичной арифметикой.

Mid range business decimal computers

The IBM 1400 series are second generation (transistor) mid range business decimal computers that IBM marketed in the early 1960s. The computers were offered to replace tabulating machines like the IBM 407. The 1400 series machines stored information in magnetic cores as variable length character strings separated on the left by a special bit, called a "wordmark," and on the right by a "record mark." Arithmetic was performed digit by digit. Input and output support included punched card, magnetic tape, and high speed line printers. Disk storage was also available. Many members of the series could be used as independent systems, as extensions to IBM punched card equipment, or as auxiliary equipment to other computer systems. Some, however, were intended for specific applications or were economical only as independent systems.

IBM provided several models compatible (or nearly so) with the 1401. 1460 is twice as fast, and many special features of 1401 were standard. 1440 was a popular lower cost alternative, although not fully compatible with the 1401. 1240, 1420, 1450 are systems specially designed for banking. 1410 is a much faster system in the same spirit as 1401, but with significant differences, such as larger memory (up to 100,000 characters), more index registers (fifteen), and additional instructions. A remarkable feature in the pre microprogramming era was a "compatibility mode" switch that allows it to run 1401 programs without change. 7010 is a faster and exactly compatible version of 1410. The IBM System/360 Model 30 could be ordered with a 1401 compatibility microprogram feature. Several 1400 series peripherals were adapted for use with System/360. Honeywell's Honeywell 200 provided approximate 1401 compatibility through a combination of architectural similarity and software support.

With the 1400 series, the smallest addressable unit in core storage is called a character. The 1400 stores alphameric characters internally in binary coded decimal (BCD) form, spanning six bits called BA8421. When the character is an operation code or is the first character in a field, another bit, called the "word mark", is included. An odd parity bit, called "C", is also included. Arithmetic is 10 based with the one's position at the high and the most significant decimal digit at the low address end of a multi digit field, thus of ″big endian″ style. This pertains for both, the (possibly indexed) address calculation for the access of operands and for the various operands of the arithmetic instructions. Whereas an address field in an instruction, designating an operand, is of fixed length (which depends on the size of the storage), the numeric operands of arithmetic instructions may be of arbitrary (positive) length. The word mark approach allows the 1410 to access a field (depending on the instruction to be performed) at either end, so that the most efficient access can be chosen. This way, the compiler of a higher level programming language has to take care of the initial increment of the operand address (by operand length minus 1) for example, for add, subtract, or multiply instructions.

Programming languages for the 1400 series included Symbolic Programming System (SPS, an assembly language), Autocoder (a more fully featured assembly language), COBOL, FORTRAN, Report Program Generator (RPG), and FARGO.

The 1400 series was replaced by System/360 and, later, by low end machines like the IBM System/3, System/32, System/34, System/36, System/38, and AS/400. The 1400s were officially withdrawn in the early 1970s, however some 1400 series peripherals were still marketed with third generation systems. Two 1401 computers have been restored to full operational status at the Computer History Museum.