Y2K and the Year 2038 Problem
22 Feb 2020 | categories: blog
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Do you remember the Y2K problem? If you don’t I’ll bring you up to speed, back in the 90s as we hurtled towards the year 2000 it became apparent that there was going to be a problem. Computers would flip their shit when the clock ticked over from December 31st 1999 to 1st January 2000. It was a whole thing, people thinking the world would end and planes would fall out of the sky.
To understand why this was an issue we need to know a little about computers back when they were in their infancy when memory was at a premium, the 50s and 60s to be precise. In 1965, for example, the PDP-7 computer[1] had a whopping 9KB of memory, which could be expanded to a eye watering 144KB.
As we got into the 70s memory had improved but not by much, this meant that when programs were being written they had to be as economical as possible when it came to memory. One way of doing that is to store and represent dates as two digits 00-99, after all this won’t be an issue in the future because computers will improve and this code won’t be running then, right? If you know anything about programming you know there is a lot of code running in production that has been there a long time. Banking is one sector that comes to mind.
Y2K
The issue here is as you reach 99 then the year 2000 will be represented as 00, but does that mean 2000 or 1900? A human can figure it out from context but computers are quite stupid. Contrary to what the public think software engineers were aware of this issue well ahead of time, people born in the 1850s were still alive when computers were gaining steam in the 1950s. Pension systems ran into issues when they were dealing with an individual who had apparently just born been born a couple of years before.
Computers weren’t just the issue here, people were putting lines in their code
like if date > 85 then pay_pension. Just makes you wonder what code you have
written that isn’t future proof. The reason Y2K wasn’t an issue (or a big one
should I say, stuff still went wrong) was people knew well ahead of time that
this was coming and worked to fix it. Some people think Y2K was some sort of
hoax, and those people are idiots.
There is a related problem I would like to talk about; have ever heard of the Year 2038 problem? Before I get to what that is I need to tell you how computers store and represent numbers in binary.
Counting in binary
Computer architecture is based around how many bits a word contains. A “word” in
this context is a sequence of bits, for example a “word” in an 8 bit computer is
8 bits long 01001101, its registers and CPU etc can work with words of 8 bits
in length.
Imagine we have a 4 bit computer, it is capable of only handling 4 bits at a
time - 0000. There are a couple of ways you can represent an integer in a
computer, let 0000 represent zero then count up from there: 0001 (1),
0010 (2), 0011 (3) etc. All the way up to 1111 which equals 15. This is
what is known as an “unsigned number”, the name will make sense in just a
moment.
Now, if you want to represent a negative number you can’t do it with this
technique, you could however sacrifice the highest bit (this one on the left
here -> 1000) and use that as a sign to tell the computer whether the number
being stored is a positive or negative number. These are called “signed”
numbers.
Signed integers
If the highest bit is a 1 then the computer would know the number is supposed
to be a negative number. One issue with signed numbers is you can no longer use
that bit to store the size of a number, so the biggest number you can represent
is a lot smaller. If you’re able to represent 0 up to the number 15 with a 4 bit
unsigned integer, then you will only be able to represent -8 (1000) to 7
(0111) with a signed integer.
In this 4 bit example the biggest negative number we can represent is 1000
(-8). If we start counting up like we normal would we get 1001 (-7), 1010
(-6), all the way up to 1111 (-1). It is implemented this way so you can have
0000 represent zero, and you can use Two’s complement[2] to get the negative
of a number which is a lot easier for a computer to do than using One’s
complement[3].
What happens happens when you have an unsigned number starting at 0000 and try
to increment to 1111 though? After you get all the way up to 0111 the next
binary number that follows is 1000, which means the integer the binary
represents jumps from 7 to -8. This is what’s known as integer overflow and is a
nasty wee bug. Fun fact: integer overflow was the original reason Gandhi was
such an asshole in the game Civilisation[4]
Architecture
My examples before were based on a 4 bit computer but these days we typically see 64 bit architecture in our computers, there are even 128 bit computers kicking around but until 64 bit computers became the norm it was 32bit computers that were all you could reasonably afford in the 1990s. In a 32 bit architecture The biggest unsigned number you can represent is 4,294,967,295 and the biggest signed integer you can represent is 2,147,483,647. Quite the difference.
Year 2038
It took some build up but here we are: these days computers use the Unix Epoch[5] to figure out the date, the epoch is the number of seconds that have elapsed since January 1st 1970. To a computer nothing existed before this time. Given that today 1,582,382,210 seconds have elapsed since the epoch a computer can tell you it’s Tues 28th of January 2020. I guess you’re smart enough to know where this is going. By the time we reach 03:14:07 on Tuesday, 19 January 2038 any 32bit computer holding the seconds since Unix epoch in a signed integer will overflow and the computer will think its 1901.
What am I supposed to do with this information?
If you’re smart you would start building that underground bunker and stocking up on rations before the nuclear fallout rains from the sky. Or you can trust software engineers will have ported all the important stuff over to 64 bit architecture before anything nasty happens. If they do it gives us 292 billion years to get sorted for the next overflow shit show.
[1] https://en.wikipedia.org/wiki/PDP-7
[2] https://en.wikipedia.org/wiki/Two’s_complement
[3] https://en.wikipedia.org/wiki/Ones%27_complement
[4] https://kotaku.com/why-gandhi-is-such-an-asshole-in-civilization-1653818245