Nerdy note! Don’t confuse Megabits (Mb) and MegaBytes (MB)

MSE_Jenny

While they sound similar, don’t confuse Megabits (Mb) and MegaBytes (MB). An MByte is a measure of storage, for things like memory sticks, and means just over a million bytes of information. Mbits also measure storage, but are commonly used for data transfer speeds for things like broadband. To really complicate it, an Mbit is an eighth of the size of a MByte.

Therefore an 8Mbps (Megabits per second) connection, at optimal performance, would download 1MB of information a second.

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AlexWright

First, there are 8 bits in a byte.
1024 bytes (or bits) make a kilobyte kB (or kilobit kb).
1024 kB make a megabyte MB. Except when calculating disk drive sizes, where magically only 1000 kB make a MB.
1024 MB make a gigabyte GB. Except when calculating disk drive sizes, where magically only 1000 MB make a GB.
Disk drive manufacturers exaggerate the capacity or their drives in this way.

Finally, when it comes to broadband speeds, they are usually quoted in Mbps (mega bits per second), but this is the raw speed of the link. The usable speed, i.e. how much data you can suck through it is usually about 80% of that, as the rest is taken up with communication overheads.

Thus, when your browser says its downloading a file at 250 kB (kiloBytes) per second, this is equivalent to 250 x 8 = 2000 kbps (kilo bits per second) which is 1.95 Mbps. Your router will probably be telling you its connected at 2.5 Mbps The difference is taken up with communications overheads.

Belnahua

"Therefore an 8Mbps (Megabits per second) connection, at optimal performance, would download 1MB of information a second."

Chance would be a fine thing!;)

andysuth

True, a bit is either a one or a zero, and a byte is eight of such.

I think it was to do with ascii designation of charaters and hexadecimal (Base 16), but not sure why.

It's just legacy that makes it so confusing.

Older modems used to be measured in bits per second, hence it evolves into megabits per second.

They'll probably standardise once it gets to gigabits/gigabytes per second, though it's hard as it would have to reach 8gigabits per second before it becomes 1gigabyte per second.

-AS

King_Of_Fools

MSE_Jenny wrote: »

Therefore an 8Mbps (Megabits per second) connection, at optimal performance, would download 1MB of information a second

To further confuse matters a megabit and a megabyte can be even more different.

A megabit is 1,000,000 bits:
http://en.wikipedia.org/wiki/Megabit

A megabyte is usually 1024 * 1024 = 1,048,576 bytes:
http://en.wikipedia.org/wiki/Megabyte

So to be precise, a true 8Mbps connection would download 1MB of information in 1.048576 seconds.

Bleepme

King_Of_Fools wrote: »

To further confuse matters a megabit and a megabyte can be even more different.

A megabit is 1,000,000 bits:
http://en.wikipedia.org/wiki/Megabit

A megabyte is usually 1024 * 1024 = 1,048,576 bytes:
http://en.wikipedia.org/wiki/Megabyte

So to be precise, a true 8Mbps connection would download 1MB of information in 1.048576 seconds.

It's not even as clear cut as that I'm afraid. Different providers can quote bitrates at different values, especially commerically. A 2Mb Access could be anything from an actual bitrate of 1936Kbit upto 2048Kbit depending on various different technical, commercial and configuration options (not that it really matters to a home user...).

For me the bottom line with broadband has always been to remember that you can only EVER download at the speed of the SLOWEST link between you and where you're downloading from. On most modern ADSL connections (say 2Mb and above), it's unlikely that this will be the couple of miles from your house to the telephone exchange (which determines your "connection speed"). It is normally your share of your broadband provider's ongoing connection to "the internet" that causes the bottlenecks. I think a lot of the fuss about connection speeds misses this point.

diveleader

andysuth wrote: »

True, a bit is either a one or a zero, and a byte is eight of such.

I think it was to do with ascii designation of charaters and hexadecimal (Base 16), but not sure why.

-AS

As I recall from my distant past (when at school) there are 10 bits to a byte - 8 bits of information and 2 check bits to perform error checking.

johnmccom

The confusion arises because people look for simple notation. The original notation was defined by computer people who decided that 1 kilo was 2 ^10 i.e. 1024 the mega was therefore 2^20, giga was 2^30 etc. This is out of step with SI units (blast the French again). which reserved the kilo for 10^3 or 1000. Basically the use of bits and Bytes is a device used to persuade people who don't look hard enough that something is bigger or faster than it really is.
By the way did you know that though eight bits is a byte 3 bits is a nybble.
SI people have tried to rename the kilobit a kibi-bit i.e. a KIlobit BInary.:eek: http://forums.moneysavingexpert.com/images/smilies/speechless-smiley-040.gif

mellowdrifter

AlexWright wrote: »

First, there are 8 bits in a byte.
1024 bytes (or bits) make a kilobyte kB (or kilobit kb).
1024 kB make a megabyte MB. Except when calculating disk drive sizes, where magically only 1000 kB make a MB.
1024 MB make a gigabyte GB. Except when calculating disk drive sizes, where magically only 1000 MB make a GB.
Disk drive manufacturers exaggerate the capacity or their drives in this way.

Not really magically. The true definition is that 1 gibibyte = 1024 mebibytes, while 1 Gigabyte = 1000 Megabytes.

The problem is that back in the day, the os's never really referred to gibibyes, mebibytes and kibibytes when really they should have.


Shortened the correct prefix is GiB for gibibyte while GB is for gigabyte.

More info here: http://en.wikipedia.org/wiki/GiB

mellowdrifter

diveleader wrote: »

As I recall from my distant past (when at school) there are 10 bits to a byte - 8 bits of information and 2 check bits to perform error checking.

A byte can have 10 bits, but usually 8.

And just for more funny info, 2 bits is called a crumb, 3 a nybble, 5 a nyckle, 10 a deckle, 16 a playte and so on (chomp, dynner and gobble)

bit itself means BInary digiT

cm233lh

johnmccom wrote: »

This is out of step with SI units (blast the French again).

What's it got to do with the French? SI is the international system - that's what the "I" stands for. The only reason that the confusion started in the first place is because the Americans did so much early work on computers and the Americans don't care about the rest of the international community or our measurement systems (blast the Americans again!)