The Bits vs. Bytes Confusion
Let's start with some background information on prefixes, by mentioning the
Metric system:
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kilo (k)* = 10 ^ 3 = 1,000 thousand
mega (M) = 10 ^ 6 = 1,000,000 million
giga (G) = 10 ^ 9 = 1,000,000,000 billion
tera (T) = 10 ^ 12 = 1,000,000,000,000 trillion
* Note that according to the Metric system, the "k" or "kilo" prefix is always
lowercase.
The binary forms of kilobytes and megabytes have become standard throughout the computer
industry, although they are incorrect uses of the SI prefixes (in the IT field lowercase "k" is used
to describe decimal kilobits, and capital "K" is used for binary kilobytes).
When used to describe Data Transfer Rate, bits/bytes are calculated as in the metric system
In data communications, a kilobit is a thousand bits, or 1,000 bits. It's commonly used for
measuring the amount of data that is transferred in a second between two telecommunication
points. Kilobits per second is usually shortened to kbps or Kbps**. Some sources define a kilobit
to mean 1,024 bits. Although the bit is a unit of the binary number system, bits in data
communications are discrete signal pulses and have historically been counted using the decimal
number system. For example, 28.8 kilobits per second (kbps) is 28,800 bits per second.
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1 bit (b) = 0 or 1 = one binary digit
1 kilobit ( kb) = 10^3 bits = 1,000 bits
1 Megabit (Mb) = 10^6 bits = 1,000,000 bits
1 Gigabit (Gb) = 10^9 bits = 1,000,000,000 bits
** Note: Although technically speaking, the term kilobit should have a lowercase
initial letter, most published reports capitalize it in abbreviation, resulting in "56
Kbps," or even the really confusing "56K." That leaves you with the sometimes
omitted lowercase "b" to distinguish between bits (b) and bytes (B). When used
as a measurement of network data transfers, or throughput, always assume the
word is bits first.
When used to describe Memory Size, or Data Storage bits/bytes are generally calculated as
some exponent of 2
In Data storage, and when describing Memory size, a Kilobyte is 2^10, or 1024 bytes. Because of
binary computer architecture and memory address boundaries, bytes are always some multiple or
exponent of two.
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1 byte (B) = 8 bits (b)
1 Kilobyte (K / KB) = 2^10 bytes = 1,024 bytes
1 Megabyte (M / MB) = 2^20 bytes = 1,048,576 bytes
1 Gigabyte (G / GB) = 2^30 bytes = 1,073,741,824 bytes
1 Terabyte (T / TB) = 2^40 bytes = 1,099,511,627,776 bytes
Although data storage capacity, such as on hard drives is generally expressed in
binary Megabytes (2^20), most Hard disk manufacturers, and some newer
BIOSes use decimal megabytes (10^6), which is slightly different and it gets
confusing...
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1 byte (B) = 8 bits (b)
1 Kilobyte (K / KB) = 10^3 bytes = 1,000 bytes
1 Megabyte (M / MB) = 10^6 bytes = 1,000,000 bytes
1 Gigabyte (G / GB) = 10^9 bytes = 1,000,000,000 bytes
1 Terabyte (T / TB) = 10^12 bytes = 1,000,000,000,000 bytes
Abbreviations Table
bit
b
0 or 1
byte
B
8 bits
kilobit
kb
1000 bits
kilobyte (binary)
KB
1024 bytes
kilobyte (decimal)
KB
1000 bytes
Megabit
Mb
1000 kilobits
Megabyte (binary)
MB 1024 Kilobytes
Megabyte (decimal)
MB 1000 Kilobytes
Gigabit
Gb
1000 Megabits
Gigabyte (binary)
GB
1024 Megabytes
Gigabyte (decimal)
GB
1000 Megabytes
Bandwidth Quick Reference Table
Bandwidth Quick Reference Table
Circuit Name:
Capacity
Comment
DS0
64 kbps
Building Block for Fractional T1
ISDN
64 kbps / 128 kbps
1 or 2 DS0's
Frame Relay
(Fractional T1)
64 kbps / 1.54 Mbps
North America
T1, DS-1
1.544 Mbps
North America
E1, DS-1
2.048 Mbps
Europe, Asia
T2, DS-2
6.312 Mbps
North America
E2
8.448 Mbps
Europe
E3
34.368 Mbps
Europe and Japan
T3 or DS3
44.736 Mbps
672 DS0's, 28 T1's
OC-1, STS1
51.840 Mbps
Optical Fiber, ATM* switches, SONET
Fast Ethernet
100.00 Mbps
Wireless Broadband
OC-3, STS3
155.520 Mbps
Optical Fiber; 3 x 51.840Mbps
OC-3c
155.520 Mbps
Optical Fiber; "c"= concatenated
T4
274 Mbps
equivalent of 6 T3's
OC-12, STS12
622.080 Mbps
Optical Fiber, ATM* switches, SONET
OC-48
2.488 Gbps
Optical Fiber, ATM* switches, SONET
OC-96
4.976 Gbps
Optical Fiber, ATM* switches, SONET
OC-192
10 Gbps
Optical Fiber, ATM* switches, SONET
OC-255
13.21 Gbps
Optical Fiber, ATM* switches, SONET
* ATM - Asynchronous Transfer Mode. ATM (asynchronous transfer mode) is a
dedicated connection switching technology that organizes digital data into 53byte cells (packets) and transmits them using digital signal technology.
Individually, a cell is processed asynchronously relative to other related cells and
is queued before being multiplexed over the line. Because ATM is designed to
be easily implemented by hardware (rather than software), faster processing
speeds are possible. The pre-specified bit rates are either 155.520 Mbps or
622.080 Mpbs.