????上周四晚間，甲骨文公司（Oracle）突然宣布，創始人拉里?埃里森將卸任CEO。埃里森擔任該職位已有37年，以后他將擔任該公司執行董事長兼首席技術官，薩夫拉?卡茨和馬克?赫德將出任思科公司聯席CEO。年屆七旬的埃里森，是科技領域迄今為止任職時間最長的首席執行官，不過，擔任首席執行官數十年之久的，并非只有埃里森一人。

????1995年1月，思科公司（Cisco）首席執行官約翰?錢伯斯開始掌舵這家位于加利福尼亞州圣荷西的網絡公司，在他的領導下，思科創造了互聯網歷史上最輝煌的業績之一，并躋身《財富》美國500強之列（1997年位列第332名），其市值超過1000億美元（1998年），2000年甚至一度成為世界上最有價值的公司（估值約5500億美元）。后來，網絡泡沫破滅，市場形勢急轉直下。

????2012年，錢伯斯表示他將在兩到四年內退休，并指定開發和銷售部總裁羅伯特?勞埃德、現場運營高級副總裁查克?羅賓斯以及服務部高級副總裁艾德扎德?奧弗比克作為繼任者候選人。正因如此，不久前，人們在等待思科發布最新盈利報告時，懷揣著特別的焦慮和期待。那天（8月14日）離錢伯斯的65歲生日只有9天。思科在發布財務業績時，是否會發布有關繼任的消息？

????當然，那天沒有發布關于領導層更替的消息，再次擊破傳言。一直以來這種傳言不勝枚舉，甚至可以追溯到十年前。多年以來，一直有消息稱錢伯斯即將退休，但時間證明每次都是謠言。這次也不例外，盡管有消息稱思科將裁員數千人。

????思科發言人向《財富》表示：“約翰一直說，下一次他提到繼任問題時，他就會宣布繼任者人選。這一點沒有變過。”

????但是，有兩件事情發生了變化。首先，錢伯斯現在65歲了，在很多公司，掌門人到了這個年齡都會被強制退休。第二，調研公司Gordon Haskett發布的一份報告仍預計錢伯斯即將宣布退休，稱思科是“一家沒有指定接班人的公司”。

????首席執行官的平均任期大約是8年。錢伯斯已擔任該職位近20年。他是如何做到的？他還能干多久？

????On Thursday evening, Oracle announced to much surprise that founder and CEO Larry Ellison will step down from his long-held post. He’ll become executive chairman and CTO, ceding the top spot to SafraCatz and Mark Hurd after 37 years. Ellison, 70, is by far the longest-serving chief in tech, but he’s hardly the only one whose time at the top can be measured by the decade.

????Cisco CEO John Chambers took the helm of the San Jose, Calif.-based networking company in January 1995 and presided over one of the great runs in the industry, pushing the company onto the Fortune 500 list (#332, in 1997) and past a market capitalization of $100 billion (1998) to become, for a brief moment in 2000, the most valuable company in the world (at about $550 billion). Then the market’s bottom fell out in the dot-com bust.

????In 2012, Chambers said that he expected to retire in two to four years, naming development and sales president Robert Lloyd, field operations SVP Chuck Robbins, and services SVP EdzardOverbeek as possible successors. For this reason, an unusual amount of anxiety and breathless anticipation accompanied Cisco’s most recent earnings report. The date, August 14, was just nine days before Chambers’ 65th birthday. Could investors expect succession news with the financial results?

????It came and passed with little leadership news, of course—another debunked retirement rumor in a long line of them that stretches back well over a decade. Chambers’ retirement has been “imminent” for years, yet the test of time has shown each and every rumor to be greatly exaggerated. This one was no exception, despite news of thousands of layoffs.

????“John has consistently said that the next time he talks about succession is when he announces succession,” a company spokesman tells Fortune. “This has not changed.”

????Two things have changed, however. First, Chambers is now 65, the symbolic age that at many companies would mandate retirement. Second, the research firm Gordon Haskett issued a report stating that the firm still expects Chambers to announce his retirement soon, calling Cisco “a company operating without a named successor.”

????The average tenure of a CEO is roughly eight years. Chambers has been in the role for almost 20. What has allowed him to buck that trend—and how much longer can he last?