>>There is some mis-information about BCD & packed decimals. I don't know about mini/mainframe architecture. But in PC, the name is "Binary Coded Decimals" or BCD. There are two types of it, "unpacked BCD" & "packed BCD".
>>
>>Unpacked BCD only consist of one digit per-byte. The lo-byte is for the digit (unsigned), the hi-byte is for other purposes.
>>Packed BCD is two digit per byte, one for each nibble (the lo-byte and the hi-byte). The leftmost digit is for sign.
>
>You are right; BCD can be either packed or unpacked. I had quite forgotten about the details, since I never used them in actual practice.
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>So, for calculations that are 100% accurate (at least for plus and minus), you have to use BCD - it doesn't matter so much whether it is packed or not.
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>>Btw, CONGRATULATIONS for you! :-))))
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>Thanks.

As Jim said, it does matter on Intel platform too. You have to choose which BCD you want to use. packed & unpacked has a specific instruction set to make it different. For instance, an unpacked BCD specifically spare the hi-byte for other purposes. It can contain a multiplier value, etc.. Then you have to use a specific instruction to perform the calculation and maybe we have to make some adjustment (another specific instruction)