External decimal items are sometimes referred to as zoned decimal items. Each digit of a number is represented by a single byte. The 4 high-order bits of each byte are zone bits; the 4 high-order bits of the low-order byte represent the sign of the item. If the number is positive, these four bits contain a hexadecimal F. If the number is negative, these four bits contain a hexadecimal D. The 4 low-order bits of each byte contain the value of the digit.
The maximum length of an external decimal item is 18 digits.
The maximum length of an external decimal item is 63 digits.