Feta and 8b/10b encoding: Difference between pages

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In [[telecommunication]]s, '''8B/10B''' is a [[line code]] that maps [[8-bit]] symbols to [[10-bit]] symbols to achieve [[Direct current|DC]] balance and bounded disparity, and yet provide enough state changes to allow reasonable clock recovery. This means that there are just as many "1"s as "0"s in a string of two symbols, and that there are not too many "1"s or "0"s in a row. This is an important attribute in a signal that needs to be sent at high rates because it helps reduce "[[intersymbol interference]]". The code was described in 1983 by Al Widmer and Peter Franaszek in the [[IBM]] Journal of Research and Development. IBM was issued a patent for the scheme the following year.

<table border="1" cellpadding="2" cellspacing="0" align="right" width="200px">

<tr><td colspan=2><center>'''Feta'''</center></td></tr>

<tr><td>Production Area</td><td>Greece</td></tr>

<tr><td>Milk</td><td>Goat, Sheep, Cow</td></tr>

<tr><td>[[Pasteurization|Pasteurized]]</td><td>See article</td></tr>

<tr><td>Texture</td><td>variable</td></tr>

<tr><td>Fat content</td><td>approx. 30% - 60%</td></tr>

<tr><td>Protein content</td><td>approx. ??%</td></tr>

<tr><td>Dimensions/weight</td><td>??cm x ??cm thick/??-??kg</td></tr>

<tr><td>Aging time</td><td>approx. ?? months</td></tr>

<tr><td>Certification</td><td>[[Protected Designation of Origin]] (in the EU)</td></tr>

</table>

As the scheme name suggests, 8 [[bit]]s of data are transmitted as a 10-bit entity called a ''Symbol'', or ''Character''. The low 5 bits of data are encoded into a 6-bit group and the top 3 bits are encoded into a 4-bit group. These code groups are concatenated together to form the 10-bit Symbol that is transmitted on the wire. The ''Data Symbols'' are often referred to as Dxx.y where xx ranges from 0-31 and y from 0-7. Standards using the 8B/10B encoding also define ''Special Symbols'' (or ''Control Characters'') that can be sent in place of a ''Data Symbol''. They are often used to indicate end-of-frame, link idle, skip and similar link-level conditions. They are referred to as Kxx.y and have different encodings from any of the Dxx.y symbols. Because 8B/10B encoding uses 10-bit symbols to encode 8-bit words, each of the 256 possible 8-bit words can be encoded in two different ways, one the bit-wise inverse of the other. Using these alternative encodings, the scheme is able to affect long-term DC-balance in the serial data stream, allowing links to be capacitively coupled.

'''Feta''' is a classic curd [[cheese]] whose tradition dates back to [[Greece]] thousands of years ago. It was originally made with [[goat]]'s or [[sheep]]'s milk, but today much is often made commercially with [[pasteurized]] [[cow]]'s milk (the firmer cow's milk version is made for export).

The encoding is normally done entirely in hardware based on lookup tables. Upper levels of the software stack should be unaware that this encoding is being used.

Genuine Feta is still made by shepherds in the Greek mountains with unpasteurized [[milk]]. Within the [[European Union]], Feta cheese is covered by a [[Protected Designation of Origin]], but imitation Feta is now made by a number of countries, most notably throughout [[Eastern Europe]] and [[Turkey]]. It is salted and cured in a brine solution (which can be either water or [[whey]]) for a week to several months. Feta drys out rapidly when removed from the brine.

Among the areas in which 8B/10B encoding finds application are [[Fibre Channel]], [[Gigabit Ethernet]], [[InfiniBand]], [[XAUI]], and audio storage devices such as the [[Digital Audio Tape]] and [[Digital Compact Cassette]] (DCC). The related [[Eight-to-Fourteen Modulation]] is used in the [[Compact Disc]] standard. The encoding scheme used in [[10 Gigabit Ethernet]]'s 10GBASE-R [[Physical Media Dependent]] (PMD) interfaces, 64B/66B, while similarly created with consideration of DC balance, maximum run length, transition density, electromagnetic emissions, and the like, is considerably different in design.

Feta cheese is white, usually formed into square cakes, and can range from soft to semi-hard, with a tangy, salty flavor that can range from mild to sharp. Its fat content can range from 30 to 60 percent; most is around 45 percent milk fat.

==External links==

See also: [[List of cheeses]], [[Cuisine of Greece]]

*[http://domino.research.ibm.com/tchjr/journalindex.nsf/0/b4e28be4a69a153585256bfa0067f59a?OpenDocument Original paper by Franaszek and Widmer].

*[http://patft.uspto.gov/netacgi/nph-Parser?Sect1=PTO2&Sect2=HITOFF&p=1&u=/netahtml/search-bool.html&r=1&f=G&l=50&co1=AND&d=ptxt&s1=4486739.WKU.&OS=PN/4486739&RS=PN/4486739 US Patent 4,486,739], the relevant document at the US Patent and Trademark Office's site.

[[Category:Computer and telecommunication standards]]

[[Category:Line codes]]

[[fr:Encodage 8b/10b]]