FORTRAN II

You can hover over the flags to see what they signify. In this listing they are mainly for absent fields in instructions.

Five octal digits, absent for pseudo-operations that did not result in any assembly.

One or more fields in several formats, related to the encoding of the instruction, absent for some pseudo-operations. The vast majority of instruction have a five-digit (octal) address part that you can look at to see the value of the expression in that field.

Today we would probably say “label”. The lone exception is with the HED psuedo-operation, which instead interpreted the first column as a character used to “head” symbols. Heading a symbol meant prefixing it with the head character and spaces to pad it to six characters (leaving it alone if it's already long enough). For example, if the head is “ L”, then LOAD is headed to L␣LOAD, but COMMON is unaffected by a head. Programmers can opt out per symbol by writing C$S, where C is the desired head character (or empty to indicate no head) and S is the name before heading. For example, C$MOV becomes C␣␣MOV, and $CPPI will always be ␣␣CPPI no matter what the head is. The point of this feature is to provide rudimentary namespace separation, so that symbols' “scope” could be limited to certain subprograms. Later assemblers supported multiple head simultaneously using the new HEAD pseudo-operation, which took an arbitrary number of heads in the variable field.

FORTRAN II does not use the heading feature very much.

When you click on a symbol in the location field, you'll be taken to its entry on the index page, described above.

Operations are either machine instructions (such as TRA or CLA or LDC, or commands for the assembler (such as BSS or TTL). When it's a machine instruction, * after the mnemonic indicates indirect addressing.

This field usually consists of comma-separated expressions (the “variable field”) and then a comment after some whitespace. The variable field can sometimes contain spaces, when the operation is BCD or BCI or VFD.

Click on a symbol in the variable field to be taken to its point of definition. Occasionally a symbol is defined on a different page from the point of reference. If you hover over a symbol, you get a tooltip showing its meaning in octal and decimal (often you can also get this information from the assembled word on the left).