INT 21 - DOS 1+ - GET FILE SIZE FOR FCB
AH = 23h
DS:DX -> unopened FCB (see AH=0Fh), wildcards not allowed
Return: AL = status
00h successful (matching file found)
FCB random record field filled with size in records, rounded up
to next full record
FFh failed (no matching file found)
Note:   not supported by MS Windows 3.0 DOSX.EXE DOS extender

See also: 2142

2123 - DOS 1+ - GET FILE SIZE FOR FCB