Size matters - The surface of the Earth and 64-bit Adressing

Blog Post created by Piesenecker_Alexander Employee on Apr 24, 2015

When IBM introduced the System/360 Architecture in 1964 the size of the Storage was limited to 16 MB, becaused

Addressing was limited to 24 bits. Two decades later, in 1983, the S/370-XA architecture answered increasing

storage requirements by expanding the addressing to 31-bit. Now it was possible to address 2 GB (1024 MB) which

is 128 times larger than the old 16 MB. While this increase in addressable storage can be visualized mentally we

are lost when looking at the latest increase in addressable storage introduced in 2000 with IBM's z/Series. That

hardware uses 64 bits for addressing which sums up in unimaginable 16 EB (Exabyte) size of Address Spaces. Now

16 EB is 8,589,934,592 times 2 GB. So we have 8.5 billion times 2 GB of storage (theoretically, only imagine the

bill when you buy 8.5 billion memory chips!). And the prefix Exa? We are used to Mega, Giga, and even Tera as

hard disks nowadays have capacities measuring in Terabytes. The next step is named Peta and after that comes

Exa! Keep in mind that every prefix is thousand times larger than the previous! So we are facing really huge


Have you ever tried to illustrate such numbers? Here is an analogy: Let the 2 GB be represented by a stadium

(baseball, soccer or football, just as you like) with dimensions of 250 x 250 m (or 800 x 800 feet). In that

scale the 16 MB are smaller than the infield of a Baseball field, the penalty area in a Soccer field or the End

Zone in an American Football field. But how large are 16 EB in that analogy? With 2 GB representing the size of

a stadium the 16 EB represent 8.5 billion times that area which sums up to the surface of the Earth including

all continents and all the oceans! Now that shows how large the increase in addressable storage is when

switching from 31-bit to 64-bit. I bet, this will fit the needs of programmers for the next decades.

And when we turn towards the other end of the analogy - which area represents the 4k page of storage, the

smallest unit of data for memory management in Assembler? That is about the size of a seat in our stadium!



Storage   Addressing     Analogy
   4 kB       12-bit     0.11 square meters or 1.2 square feet (Seat)
  16 MB       24-bit     465 square meters or 5000 square feet
   2 GB       31-bit     59,400 square meters or 639,400 square feet (Stadium)
  16 EB       64-bit     510,000,000 square kilometers or 197,000,000 square miles (Earth's surface)