Table of Contents
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Section A:
System interface
Byte
13:
Byte
14:
Byte
15:
Byte
16:
Bytes 17-32:
Byte
33:
Bytes 34-36:
Byte 12 (f3'): Backup attribute.
This bit may be set
by
any program (i.e.
a file backup utility).
On
each file alteration,
EOS will
reset
this bit.
For
CP/M
compatibility,
the meaning
of
this bit has been reversed, as referred to
DiCOS.
Extent
number.
The
extent number begins at 0
first
record
and
is incremented by 1
"after
records.
Byte
5
holds
5 bits of
the
extent
further
6 bits are stored in byte 15.
for
the
each
128
number,
Within
the directory,
this is the byte count.
When the
file
has been opened,
byte 14 holds certain
EOS flags,
which must not be changed by the user.
Second extent byte.
The lower 6 bits represent the upper
6 bits of the extent number.
Record number within the extent whose number is stored in
bytes 13 and 15.
Always less than 129.
The total number
of records of a file may be computed from (extent
number
*
128)
+
this byte.
Allocation map. Here the system enters the numbers of the
clusters occupied by the file.
If an overflow occurs,
a
new directory entry is established.
Current block number. This byte denotes the number of the
block
within the current extent which is to be processed
next.
When a file is opened,
the first 32 bytes of
the
directory
entry are copied into the
FCB.
Consequently,
byte
33
should be set to 0 before opening
a
file,
as
otherwise the system begins reading resp.
writing at the
record number found there
!
Random
block number.
This is a 3-byte number
used
for
random
access
disk I/0.
As usual on the
Z-80,
it
is
stored
in reverse order,
i. e.
least significant
byte
first (in byte 34), most significant byte in byte 36.
EOS System manual
Daeurnling & Zimmermann
Page 8
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