IBM 1400 series
The IBM 1400 series were 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.

History 
The 1401, announced on October 5, 1959, was the first member of the IBM 1400 series. It was the first computer to deploy over 10,000 units. The IBM 1410 was a similar design, but with a larger address space. The  IBM 1460 was logically but not physically identical to a fully optioned 1401 with 16,000 characters of memory, and twice as fast. The 1240 was a banking system, equivalent to the 1440 system with MICR support.  The IBM 7010 was logically but not physically identical to a 1410, and twice as fast.

Members of the 1400 series included:

 IBM 1240 - 1963 banking system
 IBM 1401 - 1959
 IBM 1410 - 1960
 IBM 1420 - 1962 high-speed bank transit system
 IBM 1440 - 1962
 IBM 1450 - 1968 Bank Data Processing System for small banks
 IBM 1460 - 1963
 IBM 7010 - 1962

Peripherals used with 1400 series machines included:

Card reader/punches: IBM 1402, IBM 1442
 Printers: IBM 1403, IBM 1443
 7 track tape drives: IBM 729, IBM 7330
 Disk drives: IBM 1301, IBM 1311
 Check processing IBM 1210
 Paper tape input/output

Compatible systems 

IBM provided several models compatible (or nearly so) with the 1401.
 1460 was 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 were systems specially designed for banking.
 1410 was 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 allowed it to run 1401 programs without change.
 7010 was 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.

Field and character coding 
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 
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.

Retirement 
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.

Notes

References 
IBM Archives: Pre-360 IBM Mainframe Family tree & chronology.

 A source for 1401, 1460 components.
 A source for 1410/7010 components.

External links

 Many IBM 1400 series manuals are online (pdf files) at http://bitsavers.org/pdf/ibm/1410/.

 
Variable word length computers
Decimal computers