Assignment 1, Solutions

Part of the homework for 22C:60 (CS:2630), Fall 2011
by Douglas W. Jones
THE UNIVERSITY OF IOWA Department of Computer Science

  1. What is your E-mail address?

    No solution offered.

    Real Homework!

  2. Background: Prior to 1928, punched cards were primarily used for numeric data, Each "character" was coded by one column on the card, by punching in just one of the 12 rows of the card. If we represent punches with 1 and no punch with 0, the character set was: 
            000000000000 space      
        100000000000 + (sometimes)    000000100000 4
        010000000000 - (sometimes)    000000010000 5
        001000000000 0                000000001000 6
        000100000000 1                000000000100 7
        000010000000 2                000000000010 8
        000001000000 3                000000000001 9

    In 1928, IBM extended their code, supporting upper case letters encoded with 2 punches (they called these multipunch codes), one punch in positions +, - or 0 (the zone punch) positions, and one punch in the 1 through 9 positions (the numeric punch): 

            100100000000 A (+ 1)          010000000010 Q (- 8)
        100010000000 B (+ 2)          010000000001 R (- 9)
        100001000000 C (+ 3)          001010000000 S (0 2)
            - - -                     001001000000 T (0 3)
        100000000010 H (+ 8)              - - -
        100000000001 I (+ 9)          001000000010 Y (0 8)
        010100000000 J (- 1)          001000000001 Z (0 9)
        010010000000 K (- 2)

    Question: Give the punched card encoding for "HELLO WORLD" (not including the quotes).

    See left column below. The right column is the answer to the next question. 

            100000000010 H (+ 8) 011000
        100000010000 E (+ 5) 010101
        010001000000 L (- 3) 100011
        010001000000 L (- 3) 100011
        010000001000 O (- 6) 100110
        000000000000 space   000000
        001000001000 W (0 6) 110110
        010000001000 O (- 6) 100110
        010000000001 R (- 9) 101001
        010001000000 L (- 3) 100011
        100000100000 D (+ 4) 010100

  3. Background: When the first computers were developed, IBM decided on a 36 bit word, allowing 3 12-bit codes to be packed per word, but this is very inefficient when 6 6-bit codes could handle the kinds of character sets in current use. This led to the development of 6-bit codes. One 6-bit code used for punched-card codes used 2 bits to encode the zone punch and 4 bits to encode the numeric punch. For each block, the zero indicated no punch, while nonzero values in that block indicated which hole was punched, from left to right. For example: 
            000000000000 space coded as 000000
        001000000000 0              110000
        000100000000 1              000001
        000000000001 9              001001
        100100000000 A (+ 1)        010001
        100000000001 I (+ 9)        011001
        010000000010 Q (- 8)        101000
        001001000000 T (0 3)        110011

    Question: Give the 6-bit encoding for "HELLO WORLD" (not including the quotes).

    See right column in answer to the previous question, but here are some notes on how this was derived, since several students had questions about this:

    Take, for example, the letter E. The 12-bit punched card code is: 

            100000010000 E (+ 5)

    This can be broken into 2 fields, the zone and numeric fields: 

            100 000010000

    Bit 1 of the zone field is punched, and bit 5 of the numeric field is punched, so the 2 and 4 bit compact encodings of these two fields are: 

            01 0101

    Putting this together, we get the 6-bit code for E: 

            010101

  4. A Problem: Give the 7-bit ASCII representation of the text "= CS:2630 =" Don't include the quotes. 
            0111101 =
        0100000 space
        1000011 C
        1010011 S
        0111010 :
        0110010 2
        0110110 6
        0110011 3
        0110000 0
        0100000 space
        0111101 =