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Oracle Performance Tuning and Optimization
(Publisher: Macmillan Computer Publishing)
Author(s): Edward Whalen
ISBN: 067230886x
Publication Date: 04/01/96

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Unit Conversions

Most people are familiar with the units of measurement commonly used in the computer industry. But to ensure that all readers of this book start out on the same foot, the following sections give quick overviews of these terms.

Powers of 10

Here is a quick review for those who may have forgotten these conversions:


Power of 10 Unit Name Actual Value

1012 Tera 1,000,000,000,000
109 Giga 1,000,000,000
106 Mega 1,000,000
103 Kilo 1,000
100
10-3 milli 0.001
10-6 micro 0.000001
10-9 nano 0.000000001
10-12 pico 0.000000000001

These are the typical ranges of numbers used in computer technology, although you don’t really see pico referred to very often. Speeds in terms of picoseconds are useful only if you are looking at the internal operations of the CPU chips themselves. At the speed of light, it takes approximately 0.3 picosecond to travel 1 millimeter.

Storage Units

Data is stored in the computer in a binary form. The units used to refer to this binary data are as follows:


Term Definition Comment

bit The smallest unit of data storage A bit is either a 1 or a 0.
nibble 4 bits This term is not commonly used.
byte 8 bits The most commonly used storage unit.
word An architecture- dependent term On some systems, a word is 16 bits; on others, a word is 32 or 64 bits.
kilobyte, Kbyte, KB Even though the term Kilo usually means 1,000, in computer terms (because we like powers of 2), a kilobyte is actually 1,024 bytes.
Megabyte, Mbyte, MB Just as with the kilobyte, the term megabyte refers to 1,024KB or 1,048,576 bytes.
gigabyte, Gbyte, GB A gigabyte is 1,024 megabytes or 1,073,741,824 bytes.
terabyte, Tbyte, TB A terabyte is 1,024 gigabytes or 1,099,511,627,776 bytes.

It is not uncommon today to hear some large data warehousing sites talk in terms of terabytes. In the next few years, we will probably hear of systems using storage in the tens and hundreds of terabytes.

Summary

This chapter defined and described various concepts with the intent of preparing you for the upcoming chapters. Be sure to look in the glossary for any other terms with which you are not entirely familiar.


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