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Asked: 2026-06-03T13:45:09+00:00

I’m learning Computer Science course and when I read to these definition, I understand.

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I’m learning Computer Science course and when I read to these definition, I understand. But I don’t know what different purpose of two presentations and why.
Here some short explanation of purpose that my book said:

Zone decimal : hightly compatible with text data.
Packed decimal : faster computing speed.

Something I want to know is:

1) in zone decimal presentation there is a zone section that duplicate every digit. Why ? I see this is no purpose 🙁

2) why they say zone decimal is compatible with text data and why packed decimaal is faster.

Thanks 🙂

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1 Answer

  1. Editorial Team

    Firstly – where are you learning CS? Those terms are from the 1960s, the more common name is BCD (Binary Coded Decimal)

    Zone decimal uses an entire byte for each digit. This means you can just print a number as if it was text (each ‘character’ stores a digit 0-9) but since there are only 10 digits and a byte can hold 256 different values this is a bit wasteful.

    Packed decimal uses the fact that 4bits can store 16different values. So you can store two digits in a byte (top 4bits and bottom 4bits). This is still a bit wasteful since you only use half the capacity. But it’s pretty easy to extract the two digits with just shift and mask operations.

    Pretty much the only place you would see BCD these days is in some low level hardware where you want to read/x-mit a digit without using a microprocessor at all. It’s easy to make a BCD counter just in transistors

    but if you want to do any maths you either have to do long multiplication on each digit like you would on paper – or convert into regular ints and back again

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