標準規格好像是 18" (45cm)，過長的排線可能會讓訊號比較難看，比較難看的話的確有可能對穩定性有傷害。
不過，訊號傳輸品質與晶片，排線線材、長度、結構和製作品質，硬碟本身都有關係。規格可當作一個基準，畢竟有很多廉價排線大概也只是把線包起來，總是需要一個參考的基準。
之前有看過有提案將 IDE 線拉到 27" (
Proposed ATA/ATAPI 80-Conductor Cable Length Extension，文中有些訊號量測)，不過這個題案好像沒成為標準。
相關網頁：
Fancy IDE leads - The Terrible Truth
http://www.dansdata.com/rcables.htm
(剛找到的一個網頁，最後有提到為何亂弄都沒事的原因)
引用:
How come they work, then? (節錄)
What may be causing you a certain amount of confusion at this juncture is the fact that there are people all over the world successfully using over-length ATA cables. Including round ones. Some people use cables 750mm or even 900mm in length, without causing any obvious explosions or outbreaks of smallpox. How so, I hear you ask...
Reason one - good enough components at each end of the cable can deal with more signal corruption than the IDE specification demands of them...
Reason two - IDE covers up data loss problems. The ATA interface has CRC error checking built in. When data's munged in transit down the cable, the error is detected and the data is resent...
CRC will always catch a one-bit error in a given data block. But if more than one bit's wrong, the CRC data may end up the same as it'd be if everything were fine.
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ATA Not-So-FAQs
http://www.lostcircuits.com/advice/atafaq/
Technical Committee T13 AT Attachment
http://www.t13.org/ 關鍵字： ata 80pin 80p ide cable Length inch 長度 排線 公分