Bits And Bytes
From Mac Guides
Bits and Bytes are common computing terms that are very confusing. They are written similarly (KBps for kilobytes per second vs. Kbps for kilobits per second) and used in similar applications, i.e. data transfer.
Bits vs. Bytes vs. Octets
"B" = byte, and "b" = bit. A byte is the amount of data that will fit in a single memory location on a computer. On modern microprocessors, one byte is nearly always equal to 8 bits, but other sizes were also commonly used in the past. A bit is a single one or a zero.
To avoid ambiguity, the word "octet" is often used in technical documents to describe an 8-bit byte.
Gigabit Ethernet will transfer data at 1000 Mbps, or 125MBps.
|1 B (byte)||8 b (bits)|
|1 KB (kilobyte)||1,024 bytes (mainstream definition) or 1,000 bytes (ISO definition)|
|1 MB (megabyte)||1,048,576 bytes (mainstream definition) or 1,000,000 bytes (ISO definition)|
|1 GB (gigabyte)||1,073,741,824 bytes (mainstream definition) or 1,000,000,000 bytes (ISO definition)|
Note: The mainstream definitions of kilobyte, megabyte and gigabyte are equivalent to the ISO definitions of kibibyte (KiB), mebibyte (MiB) and gibibyte (GiB) respectively.
To figure out how long it will take a 1MB picture to download over dial up, you can figure out the file size in bits.
1MB=1024KB=1024*1024B=1048578B 1048578B*8=8388608 bits
And at 56Kbps...
56Kbps=56000bps 8388608 bits/56000bps=149.8 seconds
It should be noted, however, that dial-up users will rarely, or more than likely never, see speeds of 56Kbps. The highest speeds a 56Kbps modem can handle due to overhead is around 53Kbps, and due to other overhead factors, most downloads on a 56Kbps modem will average about 32Kbps. 
Also, in terms of networking and data transfer, you will often see the speed marked in Mbps or Kbps. This is purely a marketing device, as it appears as if the data is moving 8 times faster than is useful to you.
When marketing much hardware such as hard drives, they are usually advertised using the less common standards-based definitions of space, ie where 1 GB = 1,000,000,000 bytes. However, in mainstream use, 1 GB = 1073741824 bytes (or 1024^3). This has the effect of making a hard disk appear larger than it actually is; for example, a hard disk advertised as 120 GB will be shown by the operating system as only a 111.76 GB disk (as 120 x 10 ^ 9 = 111.76 x 2 ^ 30). Care must be taken to understand which definition is being used in the context of the situation.