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Section A:
System interface
A.4. File control block FCB
All
system
calls
referring to disk files expect a pointer to
a
file
control block, which will be abbreviated as "FCB". An FCB is at least 33
bytes long,
or 36 bytes for random mode,
and supplies following infor-
mation to the system:
Byte
1:
Bytes
2- 9:
Bytes 10-12:
Drive
number where the file is located.
If the
default
drive is referred to, this byte is set to
~-
Otherwise, a
value of 1 means drive A,
2 drive B,
and so forth up to
16 for drive P.
In the directory entry,
Byte 1
denotes
the user area the file is associated to,
or it is set to
~ESH
for a non-existent or erased entry.
File name.
If the name is shorter than 8 characters, the
field has to padded with space characters. Only the least
significant
7
bits of each byte
are
evaluated
during
directory searches,
EOS regards the most significant bit
as
an attribute.
The attribute bits are partially
pre-
defined:
Byte 2 (fl.) : free for user purposes.
Byte 3 (f2.) : free for user purposes.
Byte 4 (f3') : free for user purposes.
Byte 5 (f4'): this
file will be erased after
despooling
resp.
after
execution
of
all
commands
contained
in
it.
Byte
6
(f5'): interface bit for system calls.
Byte
7
(f6.) : interface bit for system calls.
Byte 8 (f7
I) :
-
reserved for EOS
-
Byte
9
(£8'):
-
reserved for EOS
-.
File
type.
comparable
of the most
The
file type is interpreted
in
a
manner
to the file name, with the following meanings
significant bits:
Byte 10 (tl'): File is write protected.
Byte 11 (t2'): System
attribute.
This file will not
be
affected
by built-in commands
like
DIR,
ERA
as
long as this is not
expressively
specified.
The file may be opened from
a
different
user area when it is located in
the
user area 0,
but only in
read
only
mode.
EOS System manual
Daeumling & Zimmermann
Page 7
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