Terminology


The following terms, abbreviations and acronyms relate, in some way, to the IBM 1620:

add table The IBM 1620 performs arithmetic via table lookup. The memory locations 00300 through 00399 contain the add table. Each cell in the add table (003xy) contains the 'units' digit of the sum x + y. The flag bit is set on that table location if the sum produces a carry into the 'tens' position.
belly dancer A jumper wire with connectors that slip onto backplane wiring pins. They were used by the 1620 development engineers to test changes before committing them to wirewrap.
CADET Can't Add Doesn't Even Try - development code name for the IBM 1620.
check stop This is the generic term for the 1620 stopping due to some "error" condition. Some errors will always stop the machine such as an invalid address or instruction. Other conditions such as numeric overflow or read and write errors can be switch selected by the operator to stop or continue execution.
console area Memory locations 00000 thru 00079 where INSERT'ed console typewriter data is put. This is how initial program load is done: one presses RESET, INSERT, enters up to 7 bootstrap instructions, presses RELEASE and then START.
field Fields are a set of contiguous memory locations addressed by their right-most position in memory (highest address) and are processed right-to-left. They are terminated by a flag bit set in the leftmost (lowest address) position.
flag The fifth bit of every memory cell. The flag bit either indicates the left-most digit of a field or a negative value if set in the units position of a numeric field. A flag set on the low-order digit of an address field causes indirect addressing on machines with that feature. On the Model 2, flags over the middle three digits of an address field trigger indexing.
GPD General Products Division - the division of IBM which produced the IBM 1620.
IBM International Business Machines - the computer company which produced the 1620 data processing system.
multiply table The IBM 1620 performs arithmetic via table lookup. The memory locations 00100 through 00299 contain the multiply table. Each pair of adjacent cells in the multiply table contain the product x * y.
numeric field A field containing only numeric digits. Numeric fields are variable length and are terminated by a flag bit set in the high-order digit. Negative numeric values are stored as a true value (not complemented) with the flag bit set in the low-order digit.
product area Memory locations 00080 thru 00099 which hold the low-order 20 digits of all multiplication results. If the product is longer than 20 digits, then it extends below 00080 for as many digits as needed, wrapping around to high memory if necessary.
record Records are a set of contiguous memory locations addressed by their left-most position in memory (lowest address) and are processed left-to-right. They are terminated by a record mark and usually contain multiple fields. Records are typically useful in I/O operations.
record mark A special non-numeric "digit" in memory which indicates the right-hand end of a record.
SMS Standard Modular System - IBM's set of standardized, plug-in circuit modules used in their computer systems in the 1950's and 1960's.
SPS Symbolic Programming System - the name of the assembler for the IBM 1620.


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