This chapter is from the book
This chapter is from the book
This chapter is from the book
1s and 0s
Computers are digital devices. That means they understand 1s and 0s. One 1 or one 0 is known as a bit. In actuality, a 1 is simply a voltage level. So, when we type characters into a word processing application, the keyboard translates those characters into voltage levels. Figure 1.26 shows this concept. Notice that each letter is represented by a combination of eight 1s and 0s. Each 1 is a voltage level sent to the motherboard (and components on it). Each 0 is simply the absence of a voltage level.
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Figure 1.26 Binary bits
Technicians need to be able to describe capacities such as hard drive capacities and available drive space. Eight bits grouped together are a byte. Figure 1.27 shows a hot dog divided into eight sections (which make a big old “byte”).
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Figure 1.27 A byte
Approximately 1,000 bytes is a kilobyte (kB), as shown in Figure 1.28. 1 kB is 1,024 bytes to be exact, but industry folks simply round off the number to the nearest thousand for ease of calculation. Approximately 1 million bytes is a megabyte (MB), but a true megabyte is 1,048,576 bytes. 540 megabytes is abbreviated 540 MB, or 540 M. Notice in Figure 1.29 that a megabyte stores a lot more 1s and 0s than a kilobyte.
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Figure 1.28 A kilobyte
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Figure 1.29 A megabyte
Approximately 1 billion bytes (1,073,741,824 bytes) is a gigabyte (GB), which is shown as 1 GB or 1 G. Approximately 1 trillion bytes (1,099,511,627,776 bytes) is a terabyte, which is shown as 1 TB or 1 T. Figures 1.30 and 1.31 show how storage capacities get larger.
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Figure 1.30 A gigabyte
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Figure 1.31 A terabyte
When information needs to be expressed exactly, binary prefixes are used. For example, when describing the value 210 (1,024), instead of saying this is 1 kilobyte, which people tend to think of as approximately 1,000 bytes, the term kibibyte (KiB) is used. When describing the value 220, or 1,048,576, the term mebibyte (MiB) is used. Table 1.5 shows the terms used with computer storage capacity and binary prefixes when exact measurements are needed.
Table 1.5 Storage terms and binary prefixes
Term |
Abbreviation |
Description |
|---|---|---|
Kilobyte/kibibyte |
kB/KiB |
~1 thousand bytes/210 bytes |
Megabyte/mebibyte |
MB/MiB |
~1 million bytes/220 bytes |
Gigabyte/gibibyte |
GB/GiB |
~1 billion bytes/230 bytes |
Terabyte/tebibyte |
TB/TiB |
~1 trillion bytes/240 bytes |
Petabyte/pebibyte |
PB/PiB |
~1,000 trillion bytes/250 bytes |
Exabyte/exbibyte |
EB/EiB |
~1 quintillion bytes/260 bytes |
Zettabyte/zebibyte |
ZB/ZiB |
~1,000 exabytes/270 bytes |
Yottabyte/yobibyte |
YB/YiB |
~1 million exabytes/280 bytes |
Frequencies are also important measurements in computers because people want to know how fast their computers, processors, memory, and other parts are operating. Frequencies are shown in similar measurements, but instead of bits (b) or bytes (B), speeds are shown in hertz (Hz). A hertz is a measurement of cycles per second. Something that operates at approximately 1 million cycles per second is said to operate at 1 megahertz (1 MHz). For 1 billion cycles per second, the measurement is known as 1 gigahertz, or 1 GHz. Transfer speeds are commonly shown in bits per second, such as gigabits per second, or Gb/s, or bytes per second, such as in megabytes per second, or MB/s. Notice the capital letter B to indicate bytes as compared to the lowercase b to indicate bits. These measurements are used in a lot of IT-related hardware and software.