Research and Advances

Scanning text with a 1401

Scanning text on a computer, as in forming word lists or editing, usually involves isolating and identifying certain characters or classes of characters. For example, if we scan text to form a list of words, the definition of “word” might be “everything between two blanks that isn't punctuation.” To program this, we must be able to identify a single character (blank) and a class of characters (punctuation). In a computer such as the 7090, where characters are numbers, we can put a character into an index register and index a table of transfers (one table-entry per character), thus getting to a section of code appropriate for handling that particular character. This is not natural for the 1401 because characters are not numbers and turning them into numbers is a bit clumsy. However, 1401 addresses are a combination of numbers and other characters, and we can use characters directly to reference certain addresses provided we can turn all characters (there are 64) into the 40 that are allowable in specifying an address.


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