IBM 1620; was: 1602

Yup, the 1620. More specifically, the 1620 Model I. Later versions of the machine didn't require in-memory tables to do arithmetic. But the original version required at least the addition table and, if multiply was used, the multiplication table. This was a decimal machine, addressed by digit, with 6 bits per digit (8421+word mark+parity). Core was 12 bits wide, with odd-even locations in the same word. The neat thing is that the 1620 was a variable-word-length machine; numbers were addressed by the location of their least significant digit and terminated by the occurrence of a work mark on the most significant digit (a word mark on the least signficant signified a negative number). Records were addressed by the lowest address position and terminated by a record mark. One could manipulate numbers with thousands of digits with no particular special programming effort. Or, one could alter the arithmetic tables to do arithmetic in a different radix (sometimes this happened accidentally). Clearing memory was a matter only one instruction. A machine that was great fun, if not glacially slow. Dijkstra hated it. Here's a sample program: http://99-bottles-of-beer.net/language-ibm-1620-sps-916.html Cheers, Chuck