Art of Assembly Language, 1st Edition

4.3. 4.3 The TBYTE Data Types

HLA lets you declare ten-byte variables using the tbyte data type. Because HLA does not allow the use of 80-bit non-floating point constants, you may not associate an initializer with this data type. However, if you wish to reserve storage for an 80-bit variable, you may use this data type to do so.

The tbyte directive allocates ten bytes of storage. There are two data types indigenous to the 80×87 (math coprocessor) family that use a ten-byte data type: ten-byte BCD values and extended precision (80-bit) floating point values. Because you would normally use the real80 data type for floating point values, about the only purpose of tbyte in HLA is to reserve storage for a ten-byte BCD value (or other data type that ...