There are two kinds of FCB, the normal, whose length is 37 bytes and the
expanded one of 44 bytes.
The FCB is created of data given by the programmer and by
data which it takes directly from the operative system.
When these types of files are used it is only achievable to work on the current
directory since the FCBs do not give sport for the use of the organization by directories of DOS.
The FCB is created by the following fields:
POSITION LENGTH sense
00H 1 Byte Drive
01H 8 Bytes File name
09H 3 Bytes Extension
18H 8 Bytes Reserved
20H 1 Bytes Current register
21H 4 Bytes Random register
0CH 2 Bytes Block number
0EH 2 Bytes Register size
10H 4 Bytes File size
14H 2 Bytes Creation date
16 H 2 Bytes Creation hours
To choose the work drive the next format is followed: drive A = 1; drive B
= 2; etc. If 0 is used the drive life form used at that instant will be taken as
option.
The name of the file must be defensible to the left and for fear that it is
essential the remaining bytes will have to be filled with gaps, and the
extension of the file is placed the same method.