0040 INIT{l,IN,'LABEL' ,2)
3.5 LOGICAL UNIT ASSIGNMENT FOR THE COS SYSTEM
The assignment of logical units to physical mass storage devices provides greater utilization of the storage area and a certain device independence. The device independence is available at run time; any mass storage device can be specified for I/O and the program executes using the specified devices.
The COS system handles storage using the following hierarchy 2 characters
256 words 16 blocks
1 word 1 block 1 segment
Refer to sections 3.4.1 and 3.4.2 for background on logical unit assignment before proceeding. Devices not currently part of the system configuration can not be assigned a logical unit.
3.5.1 How Logical Units are Assigned by SYSGEN
On the system device, disk or DECtape, logical units are assigned from the end working toward the beginning of the device, but in reverse order. For example, a disk with 3 logical units would be arranged, starting from the beginning as: Directory; Monitor; System programs; User programs; Unused space; Logical Unit 1; Logical Unit 2; Logical Unit 3. If more logical units are assigned, then logical unit 1, etc. will be moved closer to the beginning of the device.
On non-system devices, disk or DECtape, logicat units are assigned in sequential order starting at the beginning of the disk or DECtape.
For example, a disk with 4 logical units might be arranged: Logical Unit 1; Logical Unit 2; Logical Unit 3; Logical Unit 4; Unused space. There is a total of 406 segments available on an RK05 disk and 46 segments on DECtape.
For example, with the following log ical unit assignments:
Logical unit Device Size (Segments)
1 DKO 40
2 DKO 20
3 DKO 10
4 DKI 60
5 DKI 40
6 DKI 20
would cause an RK05 system disk (DKO) and non-system disk (DKl) to be organized as follows:
System Disk DK.0 LU3 LU2 LUI
UNUSED SPACE
USER PROGRAM (SOURCES &
BINARIES)
SYSTEM PROGRAMS
MONITOR DIRECTORY
~ M M
Non-system Disk DKI
UNUSED SPACE
LU6 LUS LU4
~
co
N
3.5.2 COS-300 Logical unit Assignment
To make logical unit assignments from the terminal, type
~RU SYSGEN/T
and the CR key. Type the 3 character device code, a comma and length in segments in the order they are to be assigned to the logical units.
The comma and length in segments can be omitted and SYSGEN assigns all the space left on the specified device to the next logical unit (DECtape
=
46 segments; RK08 Disk, 203, segments; RK8E, 406 segments; RF08 disk, 64 segments times the number of platters). The first device entered is automatically assigned to logical unit 1, the second to unit 2, etc. For example,.RU SYSGEN/T DKO,20
DKO,20 DKO,20 DKl,lOO DKl,lOO DKl,lOO DKI END
The result of the above SYSGEN will be to assign logical units 1, 2, and 3 to RX8E drive 0; and logical units 4, 5, 6, and 7 to drive 1.
Logical unit 7 will be 106 segments long (406-300). If an error is made when typing the table, type CTRL/C then retype the RUN SYSGEN/T command ahd start the table over again. When all desired logical units have been specified, type CTRL/Z.
Logical assignment can also be accomplished by typing the table into the Edit Buffer. This method allows error correction with the Editor commands. If the following logical unit assignments are typed to the Edit Buffer,
0010 DTI 0015 DT2 0020 DT3 0025 DT4 0030 DT5 0040 DT6 0050 DT7 0060 DKO,46 0070 DKO,46 END
and the command
. RUN SYSGEN
and the CR key is typed, SYSGEN makes the logical unit assignments according to the table in the edit buffer. Logical units 1-7 are DECtape units 1-7 with a length of 46 segments and logical units 8 and
The table created with the Monitor can also be stored with the WRITE where TABLI contains
0010
LOGICAL DEVICE LENGTH
device
3.5.3 COS-310 Logical Unit Assignment
LOGICAL DEVICE LENGTH
LOGICAL DEVICE LENGTH
UNIT# NAME (SEGMENTS) assigned 46 segments. Logical units 8-15 are left unassigned. The user may assign and reassign any of the 1-15 logical units as desired. Logical unit
o
is always the system device and cannot be reassigned.The COS- 310 system is shipped with logical units 1-7 assigned to RX8E units 1-7. Each unit is initially assigned 41 segments.
It is advisable to create logical units of varied sizes since file lengths vary and a short file in a long logical unit wastes storage.
MEDIA PHYSICAL SIZES IN SEGMENTS device
RKOl RK05 RF08 DECTAPE RXOl
3.5.4 DECtape Users
segments 202 406
64/PLATTER 46
41
Although more than one logical unit can be assigned to a physical DECtape unit, i t is advisable to assign one logical unit per DECtape.
The use of two or more units per DECtape may cause excessive tape spinning; for example, if reading from one unit and writing to another located on the same physical device. In the same example, if the output unit filled and had to be replaced, i t might be necessary to dismount the tape, ~hereby also removing the needed input unit.
A DECtape is 46 segments long so the logical unit assigned to the physical DECtape unit should be assigned 46 segments.
3.5.5 Disk Users
The easiest method of assigning logical units to a disk is to think in terms of a sequence of DECtape.
A DECtape is 46 segments long.
I I
1 46
Dectape
A RF08 platter is 64 segments; and a second platter adds another 64 segments.
1 64 65 128
RF08 platter RF08 platter
1 406 purpose. However, fifty segments are suggested which leaves approximately 342 segments (140 for RK08) for logical unit assignments. Logical units on the system device are automatically assigned at the end of that device (the opposite is true of all other
which leaves approximately 342 segments for logical unit assignments.
A sample assignment might be