Floppyshop 2/Floppyshop - 2.zip/Floppyshop - 2.iso/diskmags/5791-.end/dmg-6058/files/man4.txt/man4.txt

Text File | 1998-10-24 | 26KB | 512 lines

                          Chapter Four:

                              About
              Disks, Disk Drivers, TOS, Formatting,
                   File Storage, and Copying.



Regrettably,  much  of the information regarding disk  formats  in
previous  versions  of  the manual was wrong.  This  was  due  to
misconceptions about format procedures.  These misconceptions are
widespread;  many of the formatting programs available are poorly
written:  you  risk loss of data by using them.

I  thank  Olafur Bragason of our UG for explaining  much  of  the
following to me.

It  is very difficult to talk "just about the format," as  if  we
could ignore TOS.  TOS,  ("The Operating System"),  is called  on
other  machines the DOS,  the Disk Operating System.  You  notice
this mostly as the File Selection Window. TOS keeps track of what
directories  have been moving in and out of the drive.  When  you
read a new disk,  by updating the directory window, TOS reads the
directory  and the FAT into memory.  That stays there  until  you
read  a new disk.  The old directory is erased from memory and  a
new directory is read in.

TOS is therefore an interaction between the memory, the directory
window,  the FAT, the drive, the drive head, the disk, the format
on  the disk,  and the directory on the  disk.  Complicated?  You
bet.  It is difficult to talk only about one of these.  To start,
let's look at formats.

The disk stores data.  That data must be placed on the disk in  a
fashion  so that the drive can put it there and quickly  find  it
again.  The format is a structure which helps the drive head know
where the head is on the disk.

As  a Macintosh text puts it,  the disk is like a  parking  area:
white lines have to be drawn so that the cars can go into spaces.
By  drawing  the lines correctly,  more can fit into  that  total
area.

How  a  disk is formatted (structured) is up to  the  person  who
writes  a formatting program,  within the physical limits of  the
drive mechanism.




       ASSUMING THE STANDARD FORMAT: HOW YOUR DRIVE WORKS

Your disk is divided into concentric rings,  called TRACKS. These
rings,  or TRACKS,  are divided into SECTORS.

Assuming  the  standard ST format,  track #0 is on  the  outside.
Track  #79 is near the centre.  The first few tracks and  sectors
are used for storing information about the disk and files.  There
are eighty tracks (0,1,2,3...78,79 = 80). On each TRACK (or ring)
are 9 SECTORs.  These are numbered 1,2,3,4,5,6,7,8,  and 9. Every
sector can therefore be identified: for example, Track 54, sector
4.

On a single sided disk, the data is stored as following:

Track 0, Sector 1                       = Boot Sector
Track 0, Sectors 1-6                    = FAT 1
Track 0, Sector 7 to Track 1, Sector 2  = FAT 2
Track 1, Sector 3 to Track 1 Sector 9   = Directory
Track 2 to Track 79, Sector 9,          = Files.

The  File Allocation Table (FAT) keeps a list of where your  file
gets scattered all over the disk.  For safety, TOS keeps a backup
copy on disk; this is FAT 2.

If you want to fool around with the FAT, then here are the values
for FAT entries.  The FAT has one entry for every data cluster on
the disk.  If the entry for cluster n is m,  then four things are
possible.

     m = 0 (zero), then the cluster is not in use.
     m = FF1-FF7 means that the cluster is damaged and should not
         be used.
     m = k where 0<k<FF1;  this means that cluster n is part of a
         file and that cluster k is the next cluster in the file.
     m = FF8-FFF;  this means that cluster n is the last  cluster
         in the file.

It is not necessary to know this information for using the ST.

The Directory is just that: the list of which files are active on
disk.  When looking for your files,  go to track 1, sector 3. The
directory  keeps only the name of the file,  the location of  the
first cluster for that file,  and the kilobyte size of the  file.

On a double sided disk, the data is stored as follows:

Side A, Track 0, Sector 1               = Boot Sector
Side A, Track 0, Sector 2 to 6          = FAT 1
Side A, Track 0, Sectors 7,8,9,
plus Side B, Track 0, Sectors 1 and 2   = FAT 2
Side B, Track 0, Sectors 3 to 9         = Directory
Side A and B, Track 1 to 79             = Files.

We can immediately see problems.  Most file recovery programs are
set  to look automatically in a specific area for  the  directory
sectors. A recovery program made for single sided disks will look
in track 1,  sectors 3 to 9.  But if we are using a double  sided
disk,  then  this  recovery program,  set to look  for  directory
sectors in track one,  will find files.  A double sided  recovery
program will not be able to find the directory of a single  sided
disk, because it is looking for side B, which doesn't exist.

Each  sector  holds a maximum of 512 bytes,  or  0.5KB.  This  is
effective with large files, but small files, fx SPOOLER, which is
only  497  bytes,  will be  inefficiently  stored.  The  smallest
storage unit is a CLUSTER which is two sectors.  Thus your  drive
will use a cluster,  or 1024 bytes of space,  to store 497 bytes.
The rest is ignored.

The  sector is made of a header,  the file data,  and  a  closing
remark.

As the disk head goes flying along,  it meets a new sector. First
it  reads the information in the header.  The  first  information
identifies  the  track  number.   Then  follows  the  disk   side
information,  then sector number,  size of sector,  and then  the
CRC,  the Cyclic Redundancy Code (to check for possible  errors).
Then the head reads the data in the sector. At the end is the CRC
again. This closes the sector. Now onto the next sector.

So the head reads sectors 1, 2, 3, 4, etc in a row in each track.

Now  on to the next track.  But to switch over from one track  to
the  next leaves very little time,  so to make sure that  it  has
gotten into the correct track, it waits a whole new turn in order
to read sector 1.

Therefore much of the time,  the head is being very careful about
where it is.

If the disk is new (blank),  then the drive starts at the outside
and works its way inward,  saving/reading data along the way. But
if  the  disk  has been used very  much  (files  deleted,  saved,
redeleted, etc) then lots of spaces open up between active files.
The  computer will then store data on those tracks  and  sectors,
scattering your data not in one long piece,  but here and  there,
anywhere it can find space.  This is effective for using the disk
in the best way possible,  although it will increase the time for
the process.

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

It's  a good trick (thanks,  KHS,) every once in a while to  copy
all of your files to a new,  blank disk.  Then the files will  be
re-stored in the most efficient way,  one after the other, sector
by sector,  in one long line.  This reduces access time  terrifi-
cally.  You  can  do this by transferring all your files  into  a
RAMdisk,  deleting  all the files from the disk (just throw  them
from the disk into the wastebasket),  and then saving again  from
the RAMdisk to disk.  This can save 30 to 40% time, especially on
a boot disk. This is especially effective on a Harddisk.

Place  the  large programs first onto the  disk;  those  programs
which you read only and never change.

A  "disk organizer" is very useful;  it sorts out the files on  a
disk and places them in the most consecutive way  possible.  This
is very useful on a harddisk.

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Remember,  the  disk  drive head works in the  most  careful  way
possible:  it floats over the first track and then moves  inward.
It starts at the outside the first time.

This is not however efficient:  the directory could be placed  in
the centre of the tracks,  for example, and the most distant file
would not be more than half a disk away.

TOS was written to be compatible with IBM PCs (you can find those
in  museums).  Many  users have noticed that they  can  read  IBM
formatted 3.5 inch disks.  It seemed like a good idea.  TOS,  and
the ST, was developed in only six months.

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

A double sided drive works the same way. Both heads move over the
disk,  but together,  not separately.  Hence a single sided drive
cannot  read a double sided disk because a double sided disk  has
track  one on side A and track 2 on side B and track 3 on A  side
and so on.  It reduces access time, but makes it impossible for a
single sided drive to read,  because all it finds on the top side
is track 1, 3, 5, etc.

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

A  possible  use  of  the option of giving the  disk  a  name  is
suggested  by OB.  He names the disk according to the  formatting
program so that he knows how it was formatted.

It rather difficult,  however, to change the disk name afterwards
without a new format.  VOLUME.PRG can,  in certain cases,  change
the  disk name,  but only once.  Again,  this has to do with  the
nature of TOS.

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Finally,  there  are  programs  to check  the  disk  drive  speed
(SPEED.PRG).  A correct value should be 300 to 305.  If higher or
lower,  it  is  possible that the drive is  reading/writing  data
incorrectly (the disk sectors will show up too soon/too late  for
the disk head).

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .



                      NON-STANDARD FORMATS

In  the past half year,  we have seen some very  clever  formats.
Some  of  these place sectors in  better  patterns.  Others  take
advantage  of  peculiar  aspects of the disk  head  mechanism  to
improve read/write speed.

Why  would anyone not use the standard  ST  format?  Non-standard
formats  can  do several things.  You can  format  faster  (often
just  18 seconds for a format).  You can read/write much  faster;
often more than 50% faster.  You can also put much more on a disk
(up to 55KB more per single sided disk, or even 118KB more with a
hyperformat).  If  you have 40 disks,  this can be about 2000  KB
more, just on single sided disks.

You   must  understand  how  a  non-standard  format   functions.
Otherwise, it is pretty certain that you will lose data.

Back to the number of sectors/tracks, and their layout. There can
well be more or less than 9 sectors.  Eleven sectors seems to  be
the  maximum  limit.  Amiga disks possibly have  one  sector  per
track.  There can be up to 86 tracks,  for example, instead of 79
(the first track is number 0, so "79 sectors" is actually 80). It
is  a  mechanical limit that keeps most drives from  making  more
than  82  tracks:  the better heads can go  further  towards  the
centre of the disk.

A formatting program also creates a sector called a BOOT  SECTOR.
This is used for making a boot disk.  If you use another disk for
booting, then you can choose not to have a boot sector on a disk.
Thus  you can store data on that sector.  The standard ST  format
always creates a boot sector; you can boot with any such disk.

Another  trick is to make fewer directory sectors.  The  standard
format allows space for 112 entries; you can keep up to 112 files
on a single sided disk. This is somewhat generous; you could have
for example a maximum of 64 entries. Do this by specifying only 4
directory  sectors,  instead  of 7.  That gives  you  three  more
sectors for data.

By these various methods,  then,  if you have a good disk  drive,
and  a good formatting program,  you can place 11 sectors  in  86
tracks, with no boot sector, short directory sectors, and you can
have up to 475 KB on a single sided disk.

     A STANDARD FORMAT has 357KB per side.
     An EXTENDED FORMAT has 390 KB per side.
     A FAT DISK or FAT FORMAT has 412 KB per side.
     A HYPERFORMAT  has up 475 KB or more per side.

The sectors can also be laid nonsequentially on a track.  Instead
of putting 1-2-3-4-5-6-7-8-9-10-11, the sectors can be 1-7-2-8-3-
9-4-10-5-11-6- and on to 1 again;  this cleverly gives the head a
space between each sector.  As it reads sector two,  it  finishes
and  is ready for sector 3.  But on a standard  format,  3  comes
right after 2.  That is too fast,  and hence it must wait another
turn of the disk.  A nonsequential format gives the head a  space
between sectors to get ready for the new sector:  it reads sector
2, skips sector 8, and then reads sector 3.

(There  is some discussion here about why some programs can  read
faster than others.  TEMPUS can read a file much much faster than
1st Word. Tempus possibly creates a buffer into which the file is
first placed,  and then organized for the program's use. 1st Word
will read the sector first, and then spend time organizing it and
placing  it  in word processing format.  Then it reads  the  next
sector.  But by this time, the head has already gone too far; 1st
Word  must wait for the disk to turn once again in order to  read
the second sector.  The many "Fast Read" programs thus deal  with
this aspect of 1st Word,  which is why they don't help with other
programs.)

The  first  sector on the track can also  be  "sacrificed;"  made
useless,  so  that no data is stored there.  An error is  written
onto  that  sector.  This has the advantage of letting  the  head
swing  immediately  over to the next  track,  reading  the  first
sector,  checking that it is on the correct track, and then going
onto  the  second sector,  where it can begin to  read  at  once,
instead of waiting for a new turn.

It is in exploiting characteristics of the Atari disk drive  that
"FAST FORMATS"  are made.  Since they give the head more time  to
read, by either skipping sectors or with blank final sectors, the
head reads the data correctly. These "fast" formats are safe.

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

The directory window,  the TOS,  the disk drive mechanism,  and a
misunderstanding  of the disk identification procedure all  comes
together to produce the next problem. This was widespread most of
last year,  causing many people the dreaded "directory  crashes."

The  ST  drive has a way of speeding things up.  If  you  open  a
folder and look inside and then close again,  the ST  immediately
gives  you the previous window again,  with all of the  contents,
without re-reading the disk. The ST saves some of the information
of the directory reading (the contents of the window) to  memory.
It  assumes  that you did not change disks;  it  just  reads  the
previous directory from memory.

What happens when the computer reads a new disk?  The ST uses  an
80  byte space in the memory to hold information about the  disk.
First the directory sectors are read (file names,  file  informa-
tion (date,  size,  folders, etc.). Then the FAT (File Allocation
Table,  where the file is spread over the individual sectors)  is
read into memory. The file names and folder names are sent to the
file selector window. When you enter a folder, the ST goes "down"
into a second level; it keeps the first level in memory and reads
the information for the second level.  When you go into a further
folder within a folder,  then it is "down" three levels.  As  you
move back up from the third level, it reads the second level from
memory,  not the disk.  To go from the second level to the first,
top level,  it again reads from memory.  At any  point,  whatever
level you are in, you click on a file, the ST looks at the FAT in
memory and knows where to start looking for the file on the disk.
The entire time,  the ST must be certain that you did not  change
disks:  if  you change disks,  then the FAT information  and  the
stored directories are worthless.

To  prove  this,  take  out the disk in the machine  and  put  in
another  disk (which is not write protected ("write  protect"  is
the little tab in the back corner of the disk) and was  formatted
by  the ST format menu).  The drive noticed that you took  out  a
disk  (An infrared light shines through the write  protect  hole.
The infrared light which detects write protection was blocked for
a  moment  as  the  disk went by,  and  then  for  a  moment  was
unblocked,  and  then blocked again).  Click on  OPEN  FILE.  The
drive will start up and read the directory.  Click  CANCEL.  Open
the  directory  again.  This time,  the drive  doesn't  run.  The
directory was read from memory.  Click on the grey bar at the top
of the file select window.  The window refreshes,  but the  drive
doesn't  run.  TOS  knows that you  haven't  changed  disks:  the
infrared  light wasn't blocked as if a disk had gone in and  out.
Hence it just uses the information from memory.

On every screen redraw,  which happens about 70 times per second,
TOS  takes  a look at the drive and checks whether  the  infrared
light is blocked.

Now  put a write protected disk into the drive (push the  tab  so
that the hole is open). Open file select. The drive runs, because
it knew a disk was removed.  Click Cancel. Open again. Drive runs
again.  The  light is shining through the write tab;  for all  it
knows,  a disk has been moved.  So it checks again.  Click on the
grey  bar.   The  drive  runs  again.  In  the  test  above,  the
directories were read from memory. Now, TOS reads them every time
from disk.

Since TOS,  on each screen redraw, sees the light shining, it can
only assume that the disk has been removed.

TOS is checking serial numbers.  When you format a disk, the disk
gets  a  random number as its  identification:  the  disk  serial
number. TOS checks these numbers to know whether it should make a
new  directory  reading or whether it can just use  the  previous
directory in memory.

This is where a great deal of problems come from. Most formatting
programs don't change the serial number. Apparently, most persons
who wrote formatting programs didn't know about this. Some of the
standard  documentation (the books for programmers) contain  this
error.  They don't explain that the serial number on the page  is
an example.   So the number is either set to zero or perhaps  the
same for all formats.  You end up with a box of disks which  are,
for TOS,  identical. When you start switching disks, TOS is going
to start adding each new directory to memory, thinking that it is
all the same disk:  the serial number is identical.  Imagine  the
problems if all women looked alike. This "false" serial numbering
is the reason for most of the directory crashes, directory window
problems,  opening  a folder but nothing happening,  and  "wrong"
directories  which  most  users  have  seen  if  they  have  used
formatting programs (especially FAT formats).  One frequent error
occurs  in  1stWord / Wordplus:  you open  a  directory,  open  a
folder,  and  then  switch disks and update  the  directory.  TOS
thinks  that  the same disk in in the drive (serial  numbers  are
identical) and therefore will try to go "up the directory  tree",
that is,  just return to the level above.  But there it will find
entirely different information.  If you try to save your document
at this point,  say goodbye.  TOS will get disk information  from
the first disk (where the blank sectors are,  etc).  You now have
the  second disk with an identical serial number:  TOS will  save
your document onto the second disk as if it were the first  disk.
Your data goes on top of other data. The ST uses the FAT from the
first disk to save information on the second disk.

Remember  that the directory sector holds files.  It  also  holds
folder names; but only the names, not the contents. The directory
contents  of  the folders is not kept in the  directory  sectors:
that  is  kept in the data sectors.  (Hence,  a disk can  hold  a
maximum  of only 112 files.  But if you place files in a  folder,
then you can have unlimited number of files.)

Make  a "wrong" format disk (two with identical serial  numbers).
Place  a  number of files and folders and folders in  folders  on
each.  Enter the first disk,  go down a few levels. Change disks.
Ask  for a directory re-read to read the new  directory.  The  ST
uses  the  FAT  of the first disk to find  the  contents  of  the
folder. All it is going to find in the second disk's file sectors
is stored data from that disk, not the file names which should be
there. Hence you are going to see recognizable bits and pieces of
perhaps a text file in your file selector box. At this point, the
experiment is over:  the FAT is destroyed and all of the files on
the disk is lost.

It  is therefore essential that you use formats  which  correctly
give a random serial number to a disk. If you are having problems
with  the  directory  windows,  now  you  know  why.  Use  either
the standard ST menu format, FCOPY_2.PRG or ALPHAFORMAT.PRG.

The  write-protected  directory  re-read,   which  checks  serial
numbers,   is  used  by  some  commercial  programs  as  a   copy
protection. The program is making sure that you have the original
disk somewhere on your desk.

You can recognize this problem if you have a non-standard  format
made with a poor formatter. You click on a folder to open it, and
the drive runs and the screen blinks, but nothing happens. The ST
has tried to check the serial number,  finds that it is the same,
and  simply reads the directory again.  You get a new  directory,
which is simply the one you had before.

This is why the directory window,  which otherwise works so well,
can  get so confused if you pop non-unique serial numbered  disks
in  and  out,  reading new directories  each  time,  opening  and
closing  folders.  If  the disks have been  formatted  without  a
unique serial number,  then the directory window thinks that  you
have  not  changed  disks:   the  serial  numbers  are  identical
(usually all are zero). But since it is in fact a different disk,
the identification of the sectors/tracks will be wrong.  So  when
the  ST  tries  to read the sector,  it  opens  the  folder,  but
doesn't find the correct data.  You get a totally blank directory
window.

Don't panic.  Your computer can smell panic.

Simply  give  the ST a disk which has  been  correctly  formatted
(that is:  it has a unique serial number).  The ST becomes  happy
because  now it KNOWS that the disk is different:  it performs  a
new directory reading and everything is okay again.

The  serial  number is exploited as a form  of  copy  protection.
When the original is made, the program makes a note of the serial
number.  When you make your backup copy,  your correct formatting
program will give the disk a new serial number, as it should. But
the  program  will  see that the number  has  been  changed,  and
therefore reject the copy. Ironically, a "bad" formatting program
(which  does  not set new serial numbers correctly) is  good  for
making backup copies of programs which are protected in this way.

Some copy protected programs will,  at random, cause TOS to check
the disk for the correct serial number.  You will notice that the
drive  runs  every once in a while.  TOS is checking  the  serial
numbers.  The  program  will then compare that  number  with  the
number  that  the  disk was given when it was  formatted  at  the
factory.

I wrote above that an exotic format may cause loss of data. There
are several ways.  If the serial numbers are incorrect,  then TOS
will know from the first disk where the blank sectors  are.  When
you insert the second disk with the same serial number,  then TOS
will  write data onto sectors which it thinks are blank.  If  you
have  extra sectors/tracks,  and use a sector copy program  which
does  not know how to find those sectors/tracks,  then the  extra
data will be lost.

Normally,  the information about the format of the disk is at the
beginning  of the disk.  That is usually automatically read by  a
copy  program  when the disk drive starts up;  but  if  the  copy
program  is  stupid (doesn't check for  strange/different  format
structures),  then it will apparently copy the entire disk,  and,
when  you check it,  everything seems to be there.  But since  the
special  format  stores  things in  "illegal"  places,  the  copy
program  will  not find that illegal data,  even  with  a  format
monitor  and verification ON (telling the copy PRG to verify  the
copy). Most copy PRGs don't look for those extra tracks. Parts of
your files will be missing. Asking the SHOW INFO doesn't help; it
correctly keeps the information in the directory sector that your
file is 243,678 bytes long, but that information is stored in the
directory  sector anyway;  whether the actual clusters  exist  is
another  matter.  The  only certain way to make a  backup  of  an
extended  format / fatdisk / hyperdisk is with a RAM disk  or  an
intelligent formatting program.

Again,  if  you're  going  to make a disk which  will  be  copied
repeatedly by different people (a PD disk, for example), then use
the standard 356KB format.

The  point is:  use radical formats only if you:

     Know what you are doing.
     Are using a good formatting program.
     Have a backup.