This is actually a quite standard number format. Real computers like the 6502 http://www.6502.org/tutorials/decimal_mode.html http://www.6502.org/tutorials/dec

This is actually a quite standard number format. Real computers like the 6502 http://www.6502.org/tutorials/decimal_mode.html http://www.6502.org/tutorials/decimal_mode.html and the IBM zSeries have harware support for that encoding http://en.wikipedia.org/wiki/Binary-coded_decimal#Packed_BCD http://en.wikipedia.org/wiki/Binary-coded_decimal#Packed_BCD and there are decoder chips like the 74LS48 that directly translate these nibbles to 7-segment display numbers.