Have you ever wondered what the most common phone number in the world is?

In 2011, in a computer forum, a technology nerd had an idea and raised this question. After some searching, he really found the answer. The most common number in the world is:214-748-3647 At the time, the number had approximately 285,000 search results on Google.

There are also many in China

Who exactly does this number belong to?？它怎么能同时出现在这么多网站上？

In fact, this string of numbers has "mysterious power". It is not only the most common number, but also often appears in the engineering and computer fields. If you see this string of numbers, you'd better stop and think about whether there's something wrong.

Mysterious number 2,147,483,647

2,147,483,647 is not an ordinary number.

首先它恰好是一个prime number，而且2,147,483,647这个数值等于 2^31 − 1，因此它也是8th Mersenne prime （即形式为2的整数次方减去1的质数）。

不过，2,147,483,647最重要的一个身份，Is the upper limit of counting for a 32-bit computer operating system。

The vast majority of today's computer systems date back to the IBM System/360 operating system, the world's first instruction-set compatible computer.

In this system, integers are stored in 4 bytes. One byte is 8 bits, four bytes are 32 bits, and the most significant bit is the sign bit, so only 31 bits are actually available. Because a bit has two states (0 or 1), the maximum integer that can be stored in this way is 2 to the 31st power minus 1 (0 accounts for one place), which is 2,147,483,647.

如果在系统中储存的整数超过了这个值，系统就会Integer overflow occurred（integer overflow），自动把数值转化成2,147,483,647。

Obviously, there are a large number of fishing programmers who treat the phone number as an ordinary integer and store it in 4 bytes. So when the number entered by the user is greater than 2147483647, it will automatically convert to this number. It became the most common phone number on the Internet.

If it exceeds 2,147,483,647, something terrible will happen

The number 2,147,483,647 is not only the most common phone number, but it also often makes guest appearances elsewhere.

In 2020, in the game "Original God", a player opened a plug-in and the damage value was exactly 2,147,483,647 points (because it couldn't be higher).

Doing this in the game will be banned and unethical. Don't try

Under normal circumstances, this figure is equivalent to about 2.1 billion yuan, which is completely enough. However, with the rapid development of the Internet, it is not impossible to exceed this figure.

In December 2014, the cumulative YouTube views of the online divine song "Jiangnan Style" exceeded this figure. YouTube saw the incident as a public relations opportunity and revised its counting system accordingly. The new counting upper limit is 9,223,372,036,854,775,808, which is 100 million times higher than the old counting method.

Integer overflows in the virtual world are still trivial, but in the engineering field, integer overflows can cause program crashes, and the consequences are serious.

In 2015, the Federal Aviation Administration (FAA) issued a report stating that Boeing 787 aircraft might suddenly "crash" due to integer overflow problems.

Specifically, the control component responsible for regulating the power supply to the aircraft's engine records with an accuracy of 0.01 seconds. When the aircraft flies continuously for 248 days, the timing system will reach 2,147,483,647 0.01 seconds. Then an overflow occurs, causing the control component to activate failsafe mode.

这个问题虽然可怕，但解决方案十分简单粗暴，那就是——Timing shutdown and restart。

What happens when the time comes to 2,147,483,647 seconds?

Most of the time, restarting the device will not cause the time to return to zero, such as the time displayed on your phone. The main use of this type of equipment is the UNIX time system, starting from 00 January 1, 1970:00:00 (UTC) starts counting. So, when will this system reach the timing limit? The answer is-15 years later.

In 1999, a programmer named William Porquet discovered that by January 19, 2038, 03:14:07 is exactly the 2,147,483,647 seconds from January 1, 1970. This is like the 2038 version of the "millennium bug" problem. So Porquet built a website, 2038.org, to remind peers to debug in time.

Of course, he also received a lot of such feedback:"Okay, then we will go debug again in 2037."

Porquet is worried that some unmaintained software will crash, with unknown consequences. However, Markus Kuhn, a computer scientist at the University of Cambridge, told the BBC that many old software and equipment are expected to be eliminated by then, or upgraded during the "Y2K bug" problem in 2000, and it is not expected that there will be a more serious problem than the "Y2K bug" in 2038.

When it comes to equipment elimination, at least fixed-line phones are already on this path.

在过去十年中，全世界的固话逐渐被移动电话所取代。想想你自己上一次使用固话是什么时候，就能直观感受到这种趋势。在中国，固定电话普及率从2011年的21.3部/百人下降到2021年12.8部/百人，也就是说如今 Only about one in ten people still use landline phones。

data