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1.2.2
Configurable memory sizes
MDS units are available with memory chips (RAM/EEPROM) of various sizes.
When initialising (see section 4.2) the "filehandler" must be told what type of MDS
is involved so that the correct data management system can be created.
The following table shows how the filehandler structures the various types of MDS.
Table 1-1
Memory sizes which can be formatted
Typ
MDS-capacity
(Hex)
in bytes (gross)
Enter this
Total MDS memory
parameter
capacity
when
initialising
2.045
04H
1
1.778
84H
8.189
05H
1
7.154
85H
32.765
06H
1
28.658
86H
1 ...with ECC operation (MOBY I)
1.2.3
Check sum
To minimise the time it takes the SLG to process an MDS, a check sum (2 bytes
long) is maintained in the system area of the MDS. Use of the check sum
mechanism is essential in dynamic read and write operations (see section 7.1).
Each time the contents of the directory or the FAT are modified (execution of write
commands e.g. CREATE, WRITE, ATTRIB etc.), the filehandler calculates a check
sum on the two areas and places this in the MDS system area. If two consecutive
MDSs have the same check sum, their data structures (file names, file lengths
etc.) will be totally identical.
The filehandler does not therefore need to read the directory and FAT of the
second MDS (additional time requirement), but can continue to operate with the
current (internal to filehandler) parameters.
Note:
The check sum is created from the directory and FAT only, and not from the file
contents.
FC 56
J31069-D0155-U001-A0-7618
Max. no. of files
User data bytes
(nett)
Max. number of
Max. no. of user
files that can be
bytes that can be
created
written to the MDS
16
1.680
16
1.440
32
7.456
32
6.464
64
31.488
64
27.520
Introduction
Number of
Block size in
blocks
bytes
The product of no. of blocks and block
size gives the user data length (net) in
bytes
105
90
233
202
246
215
16
16
32
32
128
128
1-5
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