Disk Sector Editor

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Screenshots - Disk Sector Editor

Disk Sector Editor atari screenshot
Disk Sector Editor atari screenshot
Disk Sector Editor atari screenshot
Disk Sector Editor atari screenshot
Disk Sector Editor atari screenshot
Disk Sector Editor atari screenshot

Information - Disk Sector Editor

GenreTape / Disk / Cartridge UtilityYear1988
Language[unknown]Publisher[no publisher]
Box / InstructionsEnglishSoftwareEnglish

Smith, Martin H.

LicensePD / Freeware / Shareware
SerialST TypeST, STe / 0.5MB
ResolutionMedium / HighNumber of Disks1 / Double-Sided / HD Installable
Dumpdownload atari Disk Sector Editor Download / MSAMIDI

Instructions - Disk Sector Editor

DISKEDIT - A sector editor (Version 1.08) 

Instruction Manual...By M.H. Smith 1988


1. Using the program
 a. Getting started
 b. Simple editing
 c. More advanced features
2. Reference section
 a. The FILE menu
 b. The MOVE menu
 c. The CHECK menu
 d. The SHOW menu
 e. The OPTIONS menu
 f. Keyboard menu selections
3. Atari disk format
 a. Physical disk format
 b. Logical disk format
 c. Root and sub directories
 d. The file allocation table

Section 1: Using the program 

Subsection a: Getting Started 

Current limitations and warnings
 If a single file on the disk is to be edited then it follows that 
the disk must have a correct file allocation table. There are checks 
in the program to prevent this but it is recommended that you do not 
use the Open File menu option on a disk when you know the FAT is 
The program is also restricted to editing standard ST disks with 2 
512 byte sectors per cluster. This should not be much of a limitation 
as I have yet to see a disk that isn't.
The program usually assumes that the Bios Parameter block on the 
disk is correct. Because of the way the program works a totally 
scrambled BPB could cause trouble if it indicates that there is a 
ridiculously large number of sectors on the disk. Again I have yet to 
see this happen but I suppose it will occur eventually.
Be careful
It goes without saying that you can do tremendous damage by careless 
use of a sector editor. If you have never used one before read the 
section on the Atari disk format first. For experimenting purposes 
set the write protect on a disk and examine it to get used to the 
program. If you ever lose any data follow this procedure:
i) Stay very calm, do not format the disk out of frustration. It 
 is very likely that most of the data is still on it.
ii) Use a bit or sector copier to make a backup of the corrupt
 disk. This may help to identify physically damaged sectors
 and you can then work on the backup copy in relative safety.
iii ) Before making any changes be sure you know what you intend to
 do, how the disk is organised and how you will be able to
 recover if you mess up.
iv) If at all possible do not write on the defective disk. Pull
 the sectors containing your data into memory and write them
 as a file onto another disk (this is covered later).
Severely damaged disks
 If the sectors on the disk are damaged in such a way that the 
controller can no longer read them then there is obviously very 
little that can be done. Take the advice of the program, open the 
window, grab the disk by its edge and throw, hard.
If the file allocation table is defective it makes the job of 
recovery more difficult but not impossible. You must locate the 
sectors on the disk which contain your data and indicate to the 
program the order they should be put in to form the file. You can 
usually spot a defective FAT when you ask to see a file and the drive 
makes a noise like it is about to break out of the case.
If you are sensible about keeping backups then you have less 
worries, usually. If you do not realise a disk is corrupt and use a 
sector copier you can back up the corruption (don't laugh I have done 
Subsection b: Simple Editing: 
Opening a disk or file 
Put the disk in question into the drive and click the Open Disk or 
Open File menu options. When you edit a disk you can move about 
between and edit all the sectors on that disk (1440 on a double sided 
disk). If you open a file you must indicate which one by using the 
file selector. You are then confined to the sectors that make up that 
The info line of the window changes to actually give information. 
It shows the sector you are at, the highest number sector available 
and flags which show the state of that sector. These are explained 
The window title changes to indicate the disk being edited or the 
full path of the file being edited.
Sector zero of the disk or file is brought into memory and displayed 
in the window.
Using the editor
The square editing cursor can be moved around with the cursor keys 
or you can point and click the mouse where you want the cursor. The 
 key acts like a left cursor.
To change one of the bytes of the sector either type a character in 
the ascii range (code 32 - 126) if the character display is on or 
type two hex digits. If you change your mind after one digit has been 
typed press the  key.
If the new value you supply differs from the one that was there 
before then the sector is considered to be changed and an indication 
of this appears on the info line of the window.
To move to a different sector press ALT-G or select the Goto Sector 
menu option. Assuming the number of the sector that you then supply 
is in range then that sector will be read from disk for editing.
Saving Changes
For now ensure that the option Caching To RAM is turned off. When 
you move off of a sector that has been changed or close the disk 
without writing changes to a sector then an alert appears asking if 
you want the changed sector written or not.
You can save the sector yourself at any time by pressing ALT-W or 
selecting the Write Sector option. This does not clear the changed 
indication as there is still a copy of the original sector in memory 
and you may recover it with the Undo Changes option or ALT-U if you 
decide that the changes were not really wanted. Then hit ALT-W again. 
this only applies until you move off of a sector. More powerful undo 
is available with the caching option enabled and is explained in the 
next section.
Subsection c: More Advanced Features
Storing changes in RAM 
With the caching option turned on and you move off of a sector that 
has been changed then it is not written to disk but is stored in 
memory, along with a copy of the sector as it was unchanged. If 
you move back to this sector it is not read from the disk again but is 
obtained from memory. An indication of this is the word  
appearing on the info line. Asking for undo changes on such a sector 
causes the display to revert to the sector as it was read from disk, 
not the last time you edited it. Thus you can be sure that the sector 
is then really unchanged.
When the disk or file is closed then you are asked if you want all 
the sectors you have changed written back to the disk (if there are 
any changes). If you confirm this then they are written. A failed 
write cancels the close option so you may select it again and retry.
The amount of free memory determines the number of sectors that you 
may store. It is up to you to be sensible.
You can force an unchanged sector to be cached by pressing ALT-C or 
selecting the Cache Sector option. The indication of this appears 
immediately on the info line.
What have I done?
If you do have caching switched on then you can get a list of the 
changes you have made by selecting the Show Changes Made option. This 
lists the byte and sector numbers of each change and what the byte 
used to be and what you changed it to.
Turn on the hardcopy option to get a printed record of the changes.
Should you decide you need a list of the changes after closing the 
disk or file it is still available until the next open which will 
clear out the cache. 
File recovery, FAT damage
If the disk you are dealing with does not have a damaged FAT then 
you can use the Show File Trace option to get a list of the sectors 
the file occupies. Remember space is allocated 2 sectors at a time 
and these are consecutive logical sectors and note that the show 
option only gives the first sector in each cluster.
If the FAT is damaged you must search the disk yourself to find the 
numbers of the sectors holding data. Use the Search for match option. 
A thing to watch for is when you have several deleted copies of a 
file on a disk. There will be several sectors holding similar data so 
make sure you get the right one.
So open the disk (don't use open file) and find out where the data 

Once you know which sectors you need visit them in the correct order 
and press ALT-M or click the Mark Sector option on each. The sector 
is brought into the cache and a double indication  and 
+MARKED+ appears on the info line.
Once all the sectors have been marked then close the disk. You will 
then get a message asking whether you want the marked sectors 
written. Click Yes and supply a file name to the hideous file 
selector. If you only have one drive (shame) change disks first. The 
sectors you marked are then written out to form the file in the order 
that you marked them.
It is highly likely that the file will not have had a length of a 
multiple of 512 so you can now load the file into Tempus or some 
inferior editor, chop off the extra garbage and save it again.
Sure is easy eh? maybe it will encourage some more backups to be 
made. Seriously: if the FAT is down what did you expect. Automatic 
recognition of which sectors happen to be in your file?
Section 2: Reference Section 
This section describes all the available menu options and even tells 
you what they are supposed to do. 

Subsection a: FILE menu
Open Disk 
This option opens up a disk for editing. You are asked which drive. 
Sector zero is then read in and displayed and you may start editing. 
This option clears out any cached sectors remaining from a previous 
Open File 
This option opens a file. You must specify the path of the file by 
using the file selector and it is then opened. The sectors holding 
the file are located and the first is read into memory for editing. 
It is displayed as being sector zero though its actual sector number 
on the disk will be different. Like the previous option this one 
clears out cached sectors.
Cache Sector 
This copies the sector being edited into the buffer and indicates 
the fact on the info line. If there is no more memory an error 
message results. Has no effect if the sector is already in the cache. 
Cached sectors may be written back to the disk when the disk or file 
is closed.
Mark Sector 
This indicates that the sector being edited is the next one in a 
file to be recovered. It is copied into the cache and a message to 
that effect is displayed on the info line. This option has no effect 
if the sector in the buffer has already been marked or you are editing 
a file, when it does not make sense, The marked sectors may be 
written out when the disk is closed.
Undo Changes 
If the sector in the buffer has been changed then it is restored to 
the state it was in when read from disk. A cached sector is not 
restored to the state before the last edit but back to its original 
state. This option does not affect the disk.
Write Sector 
This option causes the sector in the edit buffer to be written back 
to its correct place on disk. It does not affect the indication of 
whether the disk was changed. A copy of the sector as it was still 
exists and can be recovered until the sector is left. If caching is 
on then a copy of the original sector remains in the cache until it 
is cleared.
This option causes the disk or file to be closed. If you have 
changed the sector in the buffer you will get the option to write to 
disk. Similarly if you have sectors in the cache which are changed or 
have marked some sectors you will be asked whether you want these 
written out as well. The close option does not destroy data in the 
cache so the list of changed sectors is still available until the 
next open disk or file.
The same effect as the close menu option can be obtained by clicking 
the window close box. Clicking this box without a disk or file open 
causes the window to be cleared.
Can not be selected unless close has been used. This takes you out 
of the program.
Subsection b: The MOVE Menu 
Goto Sector 
After asking for a sector number then that sector will be fetched in 
for editing. You cannot exceed the maximum sector as displayed at 
the top of the screen. If a file is open then the sector read in will 
be the one at the specified position in the file, sector 1 of the 
file is never logical sector 1 on the disk.
Goto Offset 
This option is only available when you are editing a file. You must 
type in a hex offset in bytes from the beginning of the file (2,4 or 
6 digits) and the sector and byte position of this offset is 
calculated and you are moved there. This is useful when you want to 
patch a file you have examined with a monitor. Remember that 
executable files have a header which is removed on loading.
Search For Match 
If the display selected is character mode then you are asked to 
supply a character string to be searched for. Otherwise you must type 
a hex string, e.g. 0407 to search for 2 bytes.
Once this has been done the search of the disk or file starts at the 
editing cursor position and continues until the pattern is found or 
the end of the disk or file is reached.
You can stop the search at any time by holding do the right mouse 
If the search was successful then the edit cursor is moved to where 
the match was found. If you stopped the search or the pattern was not 
found then the cursor is left where it was before the search.
Next Match 
This option, available after a successful search, causes the next 
match to be sought. It always continues the search from the byte 
after the one where the last match occurred. i.e. you may move the 
cursor to examine any sectors you like between uses of this option.
Subsection c: The CHECK Menu 
Check FAT 
The file allocation table on the specified drive is read in and 
checked for consistency. Problems detected include chains of clusters 
running through bad disk clusters, cycles of clusters and a chain 
hitting a cluster marked as free.
A problem not detected is two files pointing to the same chain of 
clusters as this would mean reading all the sub-directories on the 
disk. This is a rare situation though and should be quite easy to 
Check Boot Sector 
This option reads in the boot sector of the specified drive and 
checksums it to see if it will be executed when the disk is booted 
from. This occurs if the word checksum of the disk is 1234 hex. A 
message is printed giving the result.
Most disks should not have executable boot sectors. Some protected 
software does for example. You should be suspicious of disks such as 
P.D. software that have executable boot sectors as it is one of the 
means that stupid people could use to try and do your data in. You 
could also try looking for hidden files in the AUTO folder if you are 
really paranoid.
Subsection d: The SHOW Menu 
The options in this menu have several things in common. They all 
treat the screen as a scrolling text window and display their 
information in it. If the hardcopy option is on then anything printed 
in the window appears on the printer as well.
If you are editing a disk or file and you use one of these options 
then the sector display is restored from an internal buffer when the 
output has finished.
You can pause the output by holding down the right mouse button or 
by pressing one or more of ,  or . Output 
resumes when you release the key or button.
Show Disk Info 
This option displays the data in the Bios Parameter Block of a disk. 
This includes things like the size and position of the root directory 
and FAT and how many free clusters there are left.
If the claimed number of free clusters exceeds the count of the 
number of clusters on the disk then a warning message is printed.
Show Directories 
After selecting this option you can use the file selector to pick 
the directory you are interested in. After selecting one it is 
searched for files and their name, size, creation date and attributes 
are displayed.
Show Sector 
This causes the sector being edited to be displayed in character and 
hex form. It is included so a copy of the sector can be printed out.
Show FAT 
This option reads in a file allocation table and prints it out in a 
relatively easy to read form. The cluster number is given at the left 
hand side of the output then 8 clusters follow on the line. For each 
is printed the contents of that entry and a 3 letter code indicating 
its significance.
The display often includes a lot of empty entries as it does not 
believe the count of the number of clusters on disk but always prints 
to the end of the FAT even though most of these entries do not exist.
 The meaning of the codes is as follows:
 BAD The cluster was marked bad at format time
 RES The cluster is reserved (cluster 1)
 EOF The cluster is the last one in a particular file
 USE The cluster is allocated.
??? The entry points to a reserved cluster. 
nothing The cluster is a free one
Reserved clusters should never be allocated so the presence of a 
'???' entry indicates problems. If the symbol is 'USE' then the 
number in that entry is the number of the next sequential cluster in 
the file. Follow that chain to the next one and then see what to do 
Show File Trace 
This option asks for a filename. As with Open File this option 
interprets a null filename as a request to operate on the directory 
given in the path, this allows you to find where a sub- directory 
occurs on disk.
The trace produced lists each cluster of the file in order, the 
logical sector number on disk of the first sector in the cluster is 
printed in brackets following the cluster number.
Show Changes Made 
This option scans the sectors held in the cache. For any of them 
that have been changed a record of the changes is printed. This gives 
the byte and sector number of the change and what the byte was 
changed from and to.
A printed copy of this can be very useful if you find you have done 
something very silly. It does happen you know.
Subsection e: The OPTIONS Menu 
Character Display 
This changes mode of display of the program between hexadecimal and 
character mode. It affects the sector display, the entry of data and 
the form in which you are asked to specify a search string.
Caching To RAM 
This option turns the caching of sectors on and off. With this 
option on changed sectors are not written straight back to disk but 
are stored in memory. You may make as many changes to as many sectors 
that will fit in memory as you like.
When you close the disk you can then have all the changed sectors 
written at once.
Hardcopy Of Show 
When this option is turned on then all output from the options in 
the SHOW menu is sent to the printer as well as to the screen.
Should you select a SHOW option with hardcopy enabled and the 
printer is not present or not on line then an error message is 
 Subsection f: Keyboard Menu Selections 
Certain menu options can also be accessed from the keyboard. These 
will only be accepted in cases where the menu option would be 
allowed. The keys to press are as follows:
 ALT-U Undo Changes
 ALT-W Write Sector
 ALT-C Cache Sector
 ALT-M Mark Sector
 ALT-G Goto Sector
 ALT-O Goto Offset
 ALT-F Search For Match
 ALT-N Next Match
Section 3: Atari Disk Format 
Subsection a: Physical Format 
Tracks And Sectors 
An Atari disk is either single or double sided, rumours of a triple 
sided disk under development are completely untrue!
Each side of the disk is formatted into concentric rings, called 
tracks, on standard disks there are 80 tracks, protected disks 
sometimes use more.
Each track is divided into sectors, the standard format has 9 
sectors, each holding 512 bytes per track.
So on a double sided disk this results in 2x80x9x512 bytes of 
storage space = 737280. This is known as the formatted capacity, when 
you bought the drive they will have quoted the unformatted capacity 
of 1Mb as it is bigger.
The Boot Sector 
You do not get all the above space to yourself however. To start 
with sector 0 track 0 of the first side is known as the boot sector. 
It sometimes contains boot code and always contains the Bios 
Parameter Block. This is a description of the disk indicating the 
areas reserved by the operating system and the area you may store 
data in. The block occupies 9 words in the boot sector and contains 
the following information:
Name Use 
 recsiz Size of sectors in bytes
 clsiz Size of a cluster in sectors
 clsizb Cluster size in bytes
 rdlen Length of root directory
 fsiz Size of FAT in sectors
 fatrec No of 1st sector of 2nd FAT copy
 datrec No of 1st sector for users data
 numcl No of data clusters on disk
 flags Indicates FAT format
clsizb has always seemed a little superfluous. I assume it is because 
the format was borrowed from the bad old 8086 which finds 2x512 a 
little arduous.
rdlen is the size of the root directory in sectors. This is 
described more fully later.
There are two consecutive copies of the FAT held on disk. I am not 
sure why as it has never seemed to prevent the OS screwing the disk 
If bit zero of flags is set it indicates that the FAT has 16 bit 
entries. This occurs on a hard disk. The program will at present 
refuse to edit disks with a 16 bit FAT. Floppy disks have 12 bit 
If the boot sector word checksums to 1234 hex then the code it 
contains is executed when the disk is booted from. This code can then 
do absolutely anything you like. Early model ST computers had their 
operating systems loaded from disk in such a manner.
Subsection b: Logical Format 
Logical Sectors and Mappings 
In practice the physical format of the disk can be abstracted away. 
Rather than referring to the side,track and sector of a disk you can 
refer to a logical sector. This is a number from 0 to the number of 
sectors on the disk-1. It is so arranged that logical sector 0 
corresponds to the boot sector. The device driver is responsible for 
translating the logical sector numbers into the physical disk sector 
you are referring to. Any kind of weird mapping scheme could be used 
transparently to the user.
The sector numbers in the BPB refer to logical sectors. So if the 
value of 'datrec' is 18 then it means that logical sector 18 holds 
the first data block. It may or may not be side 0,track 2 sector 1.
Sectors are not allocated to files one at a time but in clusters. A 
cluster is a group of sectors. On the ST the cluster size is 2 so 
each cluster holds 1K of data.
If the value of 'datrec' is 18 the first cluster occupies logical 
sectors 18 and 19. The file allocation table, described later, 
indicates which clusters belong to which files and which are free for 

Subsection c: Root and Sub Directories 
Where Is the Root Directory? 
The root directory can be found from the information in the BPB by 
calculating fatrec+fsiz. This area is fixed at format time thus 
implying that is a limit to the number of files that can be created 
in the root directory. 

If 7 sectors are allocated to it and each entry is 32 bytes long 
then the number of files you can have in the root directory is 
512x7/32 = 112.
Where are Sub Directories 
Sub directories are treated in much the same way as files. Instead 
of holding data they hold directory entries. They can grow 
dynamically as can files and so the limit for the number of files in 
a subdirectory depends on the size of the disk.
To find a file several levels down you start at the root and look 
for the subdirectory, say AUTO. When this is found you have the start 
cluster of the AUTO subdirectory and can search this for the next 
one. A chain of clusters exists for AUTO in the same way as an 
ordinary file and can be followed to find all the entries in it.
Sub-directories have two extra entries '.' and '..' which refer to 
the current directory and its parent directory respectively.
The Format Of a Directory Entry 
Both root and sub directories have the same format. They are a list 
of entries each of which is 32 bytes long. Values in the various 
fields are held in backwards 8086 format. To see one open up a disk 
and goto sector 11. The format of a directory entry is:
 Size and Type Usage 
 8 characters File name
 3 characters File extension
 1 byte File attributes
 10 bytes Unused
 word Creation time
 word Creation date
 word No of first cluster
 long, Length of file in bytes

If a file is deleted the first byte of the entry is set to E5 hex 
(you remember CP\M too eh?)
The start cluster number can be converted to a sector number given 
the BPB and the additional knowledge that clusters 0 and 1 do not 
exist on the disk.

You calculate ((cluster no-2 for reserved clusters) x clsiz) + 
The file attribute byte has bits set depending on what attributes 
the file has. The layout is as follows:
Bit No Usage 
 0 If set file is read only
 1 If set file is hidden from dir search
 2 If set file is a system file
 3 If set file is 11 byte volume label
 4 If set file is a subdirectory
 5 Archive bit
 6 Unused
 7 Unused

The archive bit is supposed to indicate whether a file has been 
altered since the last backup but does not seem to work on floppy 
disks. I imagine it does on hard disks or the storm of protest would 
have been pretty big.
Subsection d: The File Allocation Table 
Where Is it?

There are two copies of this on the disk. The second copy can be 
found by looking at the value of datrec in the BPB. The first copy is 
at datrec-fsiz. The FAT normally occupies 5 sectors.
For each cluster on the disk the FAT records its state. Whether it 
is allocated to a file, free, bad etc.
Format Of Entries 
The entry for each cluster occupies 12 bits. So each group of 3 
bytes in the FAT holds the data for 2 clusters.
Extracting the correct 12 bits for each entry (you can deduce how to 
do this by looking at the output of Show FAT, remember : Show FAT 
compensates for the 8086!) gives a number between 000 and FFF hex.
If the number is 000 then that cluster is free for use.
If the number is 001 then there is a problem. Cluster 1 is a 
reserved cluster and does not actually appear on the disk. The FAT 
entries for 0 and 1 are supposed to contain information about the 
If the number is 002 to FEF then it means that this number is the 
cluster number of the next cluster in the file.
If the number is FF0 to FF7 then it means that one or both of the 
sectors in that cluster were found bad at format time and the cluster 
cannot therefore be used.
If the number is FF8 to FFF it means that this cluster holds the 
last one for a file.
So by finding the start cluster of a file you can follow the chain 
of clusters in that file until you reach the last one. This might go 
something like: 003 004 005 006 FFF.
If the FAT ever gets damaged then you are in trouble!
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