Megabyte

Key takeaways

Megabyte belongs to science; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Megabyte to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Megabyte from memory before moving on to harder problems.

Reference excerpt

The megabyte is a multiple of the unit byte for digital information. Its recommended unit symbol is MB. The unit prefix mega is a multiplier of 1000000 (106) in the International System of Units (SI). Therefore, one megabyte is one million bytes of information. This definition has been incorporated into the International System of Quantities. In the computer and information technology fields, other definitions have been used that arose for historical reasons of convenience. A common usage has been to designate one megabyte as 1048576bytes (220 B), a quantity that conveniently expresses the binary architecture of digital computer memory. Standards bodies have deprecated this binary usage of the mega- prefix in favor of a new set of binary prefixes, by means of which the quantity 220 B is named mebibyte (symbol MiB).

Definitions The unit megabyte is commonly used for 10002 (one million) bytes or 10242 bytes. The interpretation of using base 1024 originated as technical jargon for the byte multiples that needed to be expressed by the powers of 2 but lacked a convenient name. As 1024 (210) approximates 1000 (103), roughly corresponding to the SI prefix kilo-, it was a convenient term to denote the binary multiple. In 1999, the International Electrotechnical Commission (IEC) published standards for binary prefixes requiring the use of megabyte to denote 10002 bytes, and mebibyte to denote 10242 bytes. By the end of 2009, the IEC Standard had been adopted by the IEEE, EU, ISO and NIST. Nevertheless, the term megabyte continues to be widely used with different meanings.

Base 10 1 MB = 1000000 bytes (= 10002 B = 106 B) is the definition following the rules of the International System of Units (SI), and the International Electrotechnical Commission (IEC). This definition is used in computer networking contexts and most storage media, particularly hard drives, flash-based storage, and DVDs, and is also consistent with the other uses of the SI prefix in computing, such as CPU clock speeds or measures of performance. The Mac OS X 10.6 file manager is a notable example of this usage in software. Since Snow Leopard, file sizes are reported in decimal units. In this convention, one thousand megabytes (1000 MB) is equal to one gigabyte (1 GB), where 1 GB is one billion bytes.

Base 2

1 MB = 1048576 bytes (= 10242 B = 220 B) is the definition used by Microsoft Windows in reference to computer memory, such as random-access memory (RAM). This definition is synonymous with the unambiguous binary unit mebibyte. In this convention, one thousand and twenty-four megabytes (1024 MB) is equal to one gigabyte (1 GB), where 1 GB is 10243 bytes (i.e., 1 GiB).

Mixed 1 MB = 1024000 bytes (= 1000×1024 B) is the definition used to describe the formatted capacity of the 1.44 MB 3.5-inch HD floppy disk, which actually has a capacity of 1474560bytes. Randomly addressable semiconductor memory doubles in size for each address lane added to an integrated circuit package, which favors counts that are powers of two. The capacity of a disk drive is the product of the sector size, number of sectors per track, number of tracks per side, and the number of disk platters in the drive. Changes in any of these factors would not usually double the size.

Examples of use

Depending on compression methods and file format, a megabyte of data can roughly be:

a 1 megapixel bitmap image (e.g. ~1152 × 864) with 256 colors (8 bits/pixel color depth) stored without any compression. 6 seconds of 44.1 kHz/16 bit uncompressed CD audio. 1 minute of 128 kbit/s MP3 lossy compressed audio. The novel The Picture of Dorian Gray, by Oscar Wilde, hosted on Project Gutenberg as an uncompressed plain text file, is 0.429 MB. Great Expectations is 0.994 MB, and Moby Dick is 1.192 MB. The human genome consists of DNA representing 800 MB of data. The parts that differentiate one person from another can be compressed to 4 MB.

See also Timeline of binary prefixes Gigabyte § Consumer confusion

References

External links Historical Notes About The Cost Of Hard Drive Storage Space the megabyte (established definition in Networking and Storage industries; from whatis.com) International Electrotechnical Commission definitions IEC prefixes and symbols for binary multiples Archived 2004-06-15 at the Wayback Machine

Illustrations

Worked examples

Example 1 — a first encounter with Megabyte

Start with the simplest possible case. Write down what Megabyte claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In science, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Megabyte before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Megabyte ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Megabyte

In research: Megabyte appears in science research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses Megabyte in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: Megabyte is common in secondary-school and first-year university syllabi. It links to neighbouring topics Units of information, so understanding it makes those chapters shorter.
In everyday life: Look for Megabyte outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

How to study Megabyte in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Megabyte means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain Megabyte out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Megabyte in simple terms?

The megabyte is a multiple of the unit byte for digital information. Its recommended unit symbol is MB.

Why does Megabyte matter?

Because it connects several science ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Megabyte?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Megabyte.