ZX Review #1-2 31 декабря 1996

Программирование

reader-reader - Recover lost data.

A. Shuravin, g.Votkinsk


          Recover lost INFORMATION.


   Although not often, but it happens that your valuable data, 
inherited computer users with great difficulty, lost. It's a 
shame! But all the same is it really a hopeless situation? 
Consider a few cases of damage information.



          1. Accidental erasure of the file.


   This is the most harmless phenomenon, if you certainly do 
not have to Mandu MOVE. The fact that in contrast to the 
MS-DOS, a TR-DOS no files are fragmented, and therefore are 
strictly one after another. So, when you delete a file on the 
disk will remain unallocated space, which is filled with the 
contents of deleted files. The file is not going away. However, 
team-CAT or LIST You will not see it. 

   What happened? Erase the file, for example, t13 + + . 
Look at some disk-doctor of the first series of eight sectors

system (zero) track. You will be able to see something like this
picture:
54 4C 57 2E 52 42 54 20 TLW.RBT
42 AE 02 92 02 03 0E 03 B
01 6C 33 2B 2B 20 20 20 13 +
43 86 BB 7A 44 45 0F 03 C zDE


   As you can see, the first symbol file t13 + + was replaced 
by Code 01 (if the file last, the symbol is replaced by code 00 
- the end of the directory). That is, to restore it, you just 
need to fix this code. And the number of bytes 244 Eighth 
logical sector of the system track to reduce by one (here 
stores information about the number of deleted files). 

   In the case where the file was the last, more complicated. 
Then we'll fix Bytes 225, 226 - number of the first free sector 
of the track; 228 - the number of files on disk, and 229, 230 - 
the number of free sectors. For this must know the structure of 
the file header: 


                       The structure of the file header


  BYTE DESTINATION



  0 ... 7 Filename (8 characters)

    8 FILE TYPE (B, C, D, #)

  9 - 10 ADDRESS beginning of the file
 11 - 12 LENGTH OF FILE

   13 Number of sectors
 14 - 15 SECTOR / TRACK BEGINNING OF FILE



   There is a faster way to recover deleted files - use the
program CONVER COMMANDER, which allows you to see
deleted files in the file pane. To restore them, simply
rename the file, summing to it the cursor and clicking with 
CAPS SHIFT and SYMBOL SHIFT, select "rename." When the

mode "+ del files" deleted files start with a red question mark.


          2. Spoiling the system track.

   In this case we can proceed in two ways. Or find somewhere
available data on disk files and copy them or try to
reset the track. The latter, unfortunately, is not always 
possible. 

   A few tips for those who enjoyed the first method.

   1. Start with text files. Find them much easier.

   2. GENS format files usually begin with the ORG.

   3. If you are looking for BASIC - files, pay attention to 
numbers 

      lines. which have the form:

      1 byte - number stroki/256

      2 bytes - the remainder of the division by 256.

   4. Copy the file you will the following program:

LD DE, # NNNN; NNNN - Track Number (MSB)

              NUMBER OF SECTORS beginning of the file
LD HL, 50000
LD BC, # NN05; WHERE NN - NUMBER OF SECTORS TO FILE
LD A, 255
CALL 15635
RET

   After its launch, you should enter into TR DOS, and give the 
following command: SAVE "FILENAME" CODE START, LENGHT, where 
FILENAME - the name again created file, START - start address 
of file (in this case 50000), LENGHT - the length of the file. 
If you need to restore a file BASICa, data or input / output, 
then change the extension by disc doctor. If you do not 
understand the meaning of these zakoryuchek, then dial BASICe 
in the following lines: 


   1910 DATA 17, N1, N2, 33.80,195,1,5, N3, 62,255,205,19,61,201

   20 FOR I = 0 TO 14: READ A: POKE (50000 + I), A: NEXT I

   30 RANDOMIZE USR 50000

and run the command RUN. Instead of N1 should be substituted
sector number, N2 - track number, N3 - number of sectors in the 
file. 

   To restore a system path, it is often difficult.
If there is damage NINTH physical sector, then it
recovery can take advantage of the table:


       The structure of the 9 th of the physical sector of the 
system track. 


   number of bytes a destination



       225 number of the first free sector

       226 rooms of the first free track

       227 type of disc # 16 - Bilateral,

                                    # 18 - one-sided

       228 the number of files on disk

     229.230 Number of free sectors

       231 sectors per track,

                              Always 16

     232,233 # 00

    234 ... 242 # 20

       243 # 00

       244 the number of deleted files

    245 ... 252 drive name (8 characters)


   However, the system path takes only 2 kilobytes, so that
will not rastochitelstom save it somewhere in svbodnom place
For example, a 160 physical track. This can be done by typing 
in some assembler such a program:

LD HL, 50000
LD DE, 0
LD BC, # 905
LD A, 255
CALL 15635
LD HL, 50000
LD DE, # 9F07
LD BC, # 906
XOR A
CALL 15635
RET

   Restore the saved system can track using
such a program:
LD HL, 50000
LD DE, # 907
LD BC, # 906
XOR A
CALL 15635
LD HL, 50000
LD DE, 0
LD BC, # 905
LD A, 255
CALL 15635
RET

   In Basic they will look like this:
1910 DATA 33,80,195,17,0,0,1,5,9,62,255,205,19,61,33,80,195,17
1920 DATA 7,159,1,6,9,175,201
20 FOR I = 0 TO 24: READ A: POKE (50000 + I), A: NEXT I
30 RANDOMIZE USR 15619: REM: SAVE "MIRROR" CODE 50000,100

1910 DATA 33,80,195,17,7,159,1,6,9,175,205,19,61,33,80,195,17
1920 DATA 0,0,1,5,9,62,255,201
20 FOR I = 0 TO 24: READ A: POKE (50000 + I), A: NEXT I
30 RANDOMIZE USR 50000


   To automatically keep track system, create a file
object code MIRROR, and renaming the Foyle in the boot BOOT, 
create new startup file:


10 RANDOMIZE USR 15619: REM: LOAD "MIRROR" CODE 50000
20 RANDOMIZE USR 50000
30 RANDOMIZE USR 15619: REM: RUN "BOOT"
typing in the TR DOS command SAVE "boot".


          3. Spoiling a separate sector.

   Here you can help out except that a special recovery program
demagnetized sectors (principle: take it to format, burn). A
opportunity to have a utility such as FUT, ADS, DCU.

   This, unfortunately, does not always work, so it is always 
advisable to do at least once a week copy files over which you 
work. 

   Sometimes it is better to make up several times a day: none
does not guarantee that during the operation can not fail in
result of which spoil the disc.

   There are cases where the system sector is unreadable 
tracks. Then, if you use the recommendations of n2, keeping 
track system at 160 physical track, just copy the entire disk 
cloning copiers type DD FULL COPY, ignoring up badsector, and 
then restore track system.


   And, most importantly, do not be lazy to do backups!

   It will save you time and hassle.