NOTES
[1]  短语by far修饰比较级与最高级，强调数量、程度等，意为“……得多，最……”，这是一个用and 连接的并列句。
[2] to make sure是不定式短语作目的状语，其后的that引导的是make的宾语从句。
KEYWORDS
Binary Coded Decimal（BCD）  二进制编码的十进制，二-十进制
ASCII          美国信息交换用标准代码
EBCDIC    扩展的二-十进制交换码
even-parity    偶检验
odd-parity        奇检验
parity checking    奇偶检验
EXERCISES
1．True／False．
（1）______  The possible symbols in the binary numbering system are 0 to 9．
（2）______The decimal value of 16 is represented in 4 bit BCD as 00010101．
（3）______Alphanumeric versions of BCD commonly use 7，or 8 bits to represent characters．
（4）______ A 6 bit alphanumeric code can represent 128 different characters．
（5）______There are four 8 bit codes in current use．
（6）______ Each 8 bit unit used to code data is called a byte．
（7）______ Eight bit codes are limited to representing 128 different characters．
（8）______ An extra check（or parity）bit is often added to each 7，or 8 bit character represented in storage so that it will be possible to detect coding errors that may occur．
（9）______ The digits that can be found in the binary numbering system are only 0s and 1s．
（10______ Using BCD we can convert the entire decimal value into a pure binary form．
2．Fill in the blanks with appropriate words or phrases found behind this exercise．
（1）Every computer stores numbers，letters and characters in a ______  form．
（2）The abbreviation BCB is derived from its full name______．
（3）Using BCD we can convert each decimal number into its binary______．
（4）In addition to four numeric place positions in an 8-bit code there are another four     
      ______positions．
（5）The most popular code used to represent data internally in personal computer is ______．
（6）The main difference between EBCDIC and ASCII-8 is______ positions．
（7）Parity checking has two types，they are ______．
（8）Any character can be represented by using just______of 0 and 1．
  a．equivalent
  b．even-parity and odd-parity
  c．ASCII
  d．coded
  e．two digits
  f．patterns of zone
  g．zone bit
  h．binary coded decimal

1．（1）f  （2）f  （3）t  （4）f（5）f  （6）t  （7）f （8）t（9）t  （10）f

2．（1）d  （2）h  （3）a  （4）g（5）c  （6）f  （7）b  （8）e