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Thursday, June 30, 2011

Computer Architecture # 03 : Arithmetic: FIXED POINT ADDITION AND SUBTRACTION (2)


3.2 FIXED POINT ADDITION AND SUBTRACTION
The addition of binary numbers and the concept of overflow were briefly discussed in Chapter 2. Here, we cover addition and subtraction of both signed and unsigned fixed point numbers in detail. Since the two’s complement representation of integers is almost universal in today’s computers, we will focus primarily on two’s complement operations. We will briefly cover operations on 1’s complement and BCD numbers, which have a foundational significance for other areas of computing, such as networking (for 1’s complement addition) and hand-held calculators (for BCD arithmetic.)


Computer Architecture # 03 : Arithmetic: OVERVIEW (1)


3.1 OVERVIEW
In the previous chapter we explored a few ways that numbers can be represented in a digital computer, but we only briefly touched upon arithmetic operations that can be performed on those numbers. In this chapter we cover four basic arithmetic operations: addition, subtraction, multiplication, and division. We begin by describing how these four operations can be performed on fixed point numbers, and continue with a description of how these four operations can be performed on floating point numbers. 

Computer Architecture # 02 : Data Representation: CHARACTER CODE (17)


2.5 CHARACTER CODE
Unlike real numbers, which have an infinite range, there is only a finite number of characters. An entire character set can be represented with a small number of bits per character. Three of the most common character representations, ASCII, EBCDIC, and Unicode, are described here.


2.5.1 THE ASCII CHARACTER SET
The American Standard Code for Information Interchange (ASCII) is summarized in Figure 2-13, using hexadecimal indices.

Wednesday, June 29, 2011

Computer Architecture # 02 : Data Representation: CASE STUDY: PATRIOT MISSILE DEFENSE FAILURE CAUSED BY LOSS OF PRECISION (16)

2.4 Case Study: Patriot Missile Defense Failure Caused by Loss of Precision
During the 1991-1992 Operation Desert Storm conflict between Coalition forces and Iraq, the Coalition used a military base in Dhahran, Saudi Arabia that was protected by six U.S. Patriot Missile batteries. The Patriot system was originally designed to be mobile and to operate for only a few hours in order to avoid detection.
The Patriot system tracks and intercepts certain types of objects, such as cruise missiles or Scud ballistic missiles, one of which hit a U.S. Army barracks at Dhahran on February 5, 1991, killing 28 Americans. The Patriot system failed to track and intercept the incoming Scud due to a loss of precision in converting integers to a floating point number representation.

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