Disk Image FAQ

How is a REAL Atari disk organized?

What does 'Density' mean?

What does 'Double Sided' mean?

What formats do the most common Atari Disk Drives produce?

How can I tell what format my real disks are in?

What is a 'Disk Image'?

What are the most common types of 'Disk Images'?

What type of disk images should I use?

Do all Atari programs work with disk images?

How do I convert one disk image type to another?

How do I download and use pre-made disk images?

How do I make a new EMPTY disk image?

How do I format a blank disk image?

How do I convert a REAL diskette into a disk image?

What does 'Copy Protected' mean?

How do I copy a disk image onto a REAL disk?

How do I put my favorite DOS on a disk image?

How do I create a big hard disk sized image?

What Atari DOS Systems will support a large hard disk?

How do I format and write DOS to a big hard disk image?

How do I take a file from my PC's hard disk and put it into a disk image?

How do I get a file off a disk image and onto my PC's hard drive?

I have a disk image, how do I boot my Atari from it with APE?

Technical: How is an ATR file formatted?

Technical: What extensions to the ATR format does APE provide?


©2000 Steven J Tucker

How is a REAL Atari disk organized?

Atari disks, like nearly all other floppy disk computers, uses a system of 'tracks' and 'sectors' to physically organize data on magnetic disks.

Typically an Atari disk will contain 40 'tracks'. Each of these 'tracks' is a thin concentric circular area on the disk, larger at the edges of the disk, smaller at the hub.

The computer in the Atari disk drive typically divides each of these circles up into 18 separate parts called 'sectors'. Each sector can hold 128 bytes of your data.

All of this complexity is of course hidden from you for ease of use, and what you typically see is a formatted diskette that can simply store 720 sectors of data.

This is the layout typically called 'Single Density' by Atari users, and is produced by the Atari 810 and compatible drives.

Enhanced drives can produce a variety of other formats, some which can store more data.

What does 'Density' mean?

Atari users typically use the term 'Density' to describe the number of bytes a particular disk format can store per sector.

Typically 'Single Density' refers to a diskette with 720 sectors, and 128 bytes per sector, while 'Double Density' refers to an enhanced recording method that provides a format capable of 720 sectors and 256 bytes per sector.

'Single Density' yields 90kb per disk, and 'Double Density' 180k per disk.

Unfortunately the term 'Density' is quite commonly misused, even by Atari, which makes the descriptions of other formats difficult to decipher for the novice user.

The term '1050 Double Density' or '1050 Enhanced Density' describes an higher storage mode of the Atari 1050 disk drive. This format provides only 128 bytes per sector (Single Density), but puts 26 sectors on every track. This format yields 130kb per disk.

The term 'Quad Density' if often used to describe a disk drive that produces a disk with a double density format on both sides, yielding a combined total of 1440 sectors of storage. This format yields 360kb per diskette.

What does 'Double Sided' mean?

A true 'Double Sided' format requires an enhanced disk drive that puts read/write heads on both sides of the disk at once. Nearly all Atari drives are Single sided, with a read/write head reading/recording on the underside of the diskette only.

A true double-sided drive provides twice as much storage per disk than a single sided drive because it makes use of two recording surfaces instead of one.

Because Atari disk drives are soft sectored, and do not use the timing hole of the diskette, its possible to cut an extra write-protect notch into a disk, flip it over, and record again on the other side. These disks are commonly referred to as 'flippies', but are NOT double-sided.

What formats do the most common Atari Disk Drives produce?

Atari 810: The Atari 810 Disk Drive was the first drive sold by Atari, and its 'Single Density' format became the standard which all Atari drives had to be able to read and write.

Every commercial piece of software ever produced for the Atari, with the exception of 2 or 3 titles was produced in Single Density.

The 'Single Density' format has 1 Side, 40 Tracks, 18 Sectors Per Track, and 128 bytes per sector. It uses the FM recording method. The ATR equivalent of this format is a single density, 720 sector image.

Atari 1050: Ataris next drive, the 1050 Disk Drive by default read and wrote disks in the Atari 810 Single Density format. It also produces a '1050 Enhanced Density' format that provides more storage. This special format uses 1 side, 40 tracks, 26 sectors per track, and 128 bytes per sector. 'Enhanced Density' uses the MFM recording method, and the ATR equivalent is a 1040 sector, single density image.

Atari XF551: Ataris last US released drive was a true double-sided, double-density drive. It uses 40 tracks, 18 sectors per track, 256 bytes per sector, and used BOTH sides of the disk, yielding 360k of storage per disk. The equivalent ATR is a 1440 sector, double density image.

3rd Party 'Double Density': Many 3rd party vendors like Indus quickly took advantage of the MFM recording capability of newer floppy disk controllers to produce the 2nd most popular Atari format, 'Double Density'.

Drives capable of producing double density formatted disks include specially modified 1050' (upgraded with US Doubler, Happy, Speedy, etc), the Indus GT, Rana, Percom (some models), Atari XF551, and many others.

This format uses 1 side, 40 tracks, 18 sectors per track, and 256 bytes per sector. The equivalent ATR is a 720 sector, double density image.

How can I tell what format my real disks are in?

Determining the format and density of found or forgotten diskettes can be tricky if you dont have the original equipment they were recorded with.

For best results, start with a disk drive that is capable of both single and double density, such as the Indus GT or a US Doubler upgraded 1050. Without a double density capable drive, any double density disks will be unreadable, and appear to be blank.

First try to boot the disk to see if it is formatted. If you hear a number of sectors read in instead of a 'boot error', you can be sure the disk is Atari formatted.

An experienced Atari user can tell if a disk is single or double density just by listening to it boot, but the difference may not be obvious if you are new to the Atari.

The drive sends 128 bytes for every sector of a single density disk. This means the beeps you hear while loading are always the same length. A double density disk causes the drive to send 3 128 byte sectors for the first 3 sectors of the boot, then 256 byte sectors for the rest. This difference in length can be recognized by the longer beeps in the second part of the boot process.

Or you can take a DOS like MyDOS 4.5 which can be told to switch between density modes using the 'O' option. Try setting the drive to single density, then reading the directory of the target disk, if that fails, try double density.

True double-sided disks are rare since true double-sided Atari drives are rare, overall. You will find however that many if not most disks you will find have data on the back side, made into a 'flippie' by adding an extra notch to the disk. Some will have data on the back side even without the notch since the write-protect bypass switch was an easy and popular drive modification.

 

What is a 'Disk Image'?

A real Atari disk is a complex mess of adhesive magnetic stuff, made sense of by a dedicated floppy disk controller and then made useable by a computer in the disk drive. All these things boil the structure of the real disk down to a specific number of useable sectors for each recording surface, each of a fixed length.

A disk image contains only the part of a real disk the Atari Computer can see or use, its fully processed data. An ATR disk image contains 16 bytes of data that identify it as an Atari disk image, and the remainder is every byte of useable data off the original diskette, stored in the original order it was stored on the disk.

What are the most common types of 'Disk Images'?

The 5 most common types of disk images you might come across are (identified by their filename extensions):

ATR: Nick Kennedy's SIO2PC Atari Disk Image format. This is the defaco standard disk image, used by APE, SIO2PC, and all Atari emulators. There are minor differences in the header use between these programs, but the images remain compatible regardless of what program they are created with.

XFD: Xformer Disk Image. This image is similar to the ATR but lacks the ID and format header, it is essentially a large unmarked blob of data. Compatible only with the PC-Xformer emulator.

DCM: Compressed Disk Communicator image. This is actually a native Atari file format which contains an entire Atari disk compressed with Bob Puff's Disk Communicator program. Must be decompressed to an ATR before use.

SCP: Spartados Compressed Disk Image. This is also a native Atari file format, an image of a complete disk compressed with the Spartados utility SCOPY. Must be decompressed into an ATR before use.

PRO: A proprietary disk image formatted used by APE and the ProSystem. Contains an image of a copy-protected Atari disk, useable only with APE.

What type of disk images should I use?

When converting your real disks to images, you should always try to use ATR images because they are supported by nearly every emulator.

If your disks are copy protected, and you are using APE, you can create a .PRO image of these disks for use with APE.

Do all Atari programs work with disk images?

Any software that is not copy protected will work perfectly fine on disk images. In fact better since emulators generally can provide data to the Atari much faster than a standard floppy drive can.

APE has a number of ProSystem emulation modes that can handle most if not all copy protected software using its .PRO image format.

How do I convert one disk image type to another?

There are a number of utilities available to convert disk images between the various formats.

One such utility is Imagic, available in both DOS and Win32 versions.

How do I download and use pre-made disk images?

Downloading a disk image can be done the same as downloading any other file. Just select 'Save to Disk' when prompted, remember the location you saved it to, and then load they file into your emulator.

With APE, use the 'Load Image' command to load the file into drive 1, then boot the Atari from APE.

How do I make a new EMPTY disk image?

Each emulator program has its own method for creating new disk images. With APE, use the 'C' keyboard command to create a new image. Give it a filename, select an image size, and APE will do the rest.

With APE'98, use the File -> New Disk Image -> ATR menu option. You will be prompted for the filename and image size.

How do I format a blank disk image?

When you create a blank disk image, its completely filled with zeros. This is an unusual state for those used to using floppies because when DOS low level formats a disk, it also writes a directory structure and boot sectors to it.

In order to use your new completely blank disk image, you need to format it with your favorite DOS. Your dos will then lay out the directory on that image as if it were a real disk, and it will be ready for use.

You can load your blank image into any drive slot, then just use the regular DOS format command on that image. If you are using an Atari compatible DOS and want system files on the disk to make it bootable (DOS.SYS & DUP.SYS), use the 'Write DOS Files' command to then add these files to the image, just as if it were a real disk.

How do I convert a REAL diskette into a disk image?

The easiest way to convert a whole Atari disk to a disk image is by a process called 'sector copying'. You may have used this method on your Atari to duplicate a real floppy disk.

Method #1: (Using APE or APE'98, the Atari Computer, and a real Atari disk drive)

  1. Load APE and attach your APE interface, being sure to verify it is working.
  2. Attach your real Atari disk drive to the SIO bus, configure it as drive 2.
  3. Turn on the real disk drive.
  4. Load the APE_WARP.ATR image into drive 1. This disk image is included in the APE distribution package.
  5. Boot your Atari from the APE_WARP.ATR image in drive 1.
  6. When the dos-loader menu appears, select the 'MYCOPIER' program.
  7. Once MYCOPIER has loaded, release the APE_WARP.ATR image from drive 1.
  8. Insert the diskette you want to convert into the real disk drive.
  9. Create a new blank ATR image that matches the capacity of the real disk you are going to read, load this new ATR into drive 1.
  10. Configure MyCopier with the SOURCE drive as 2 (real drive), and the DESTINATION as drive 1 (disk image).
  11. Press START on the Atari to start the sector copy. Once complete the disk image in drive 1 will be an exact duplicate of the real disk in drive 2.
  12. Return to step 8 to image more disks.

Method #2: (Using the DOS ProSystem and a real Atari disk drive)

  1. Load the ProSystem program on the PC and attach your ProSystem interface. The interface should attach to the PC's serial port on one end, and an Atari disk drive on the other.
  2. Configure the Atari disk drive as drive 1, this is VERY important.
  3. Turn on the Atari disk drive and insert the disk you wish to image.
  4. To create a ATR image of an normal diskette, press 'A' on the PC. To create a PRO image of a copy protected diskette, press 'P' on the PC.
  5. Return to step 3 to image more disks.

Method #3: (Using ProSystem'98 and a real Atari disk drive)

  1. Load the ProSystem program on the PC and attach your ProSystem interface. The interface should attach to the PC's serial port on one end, and an Atari disk drive on the other.
  2. With the ProSystem'98 software you may attach up to 4 disk drives at once. Each drive must have a unique drive ID, but need not start at drive 1.
  3. Turn on the Atari disk drive(s) and insert the disk(s) you wish to image. If using more than one drive, insert ALL the disks you wish to image.
  4. To create ATR images, use the 'Create ATR image(s) from Real Disks' menu option. To create PRO images from copy protected diskettes, use the 'Create PRO Image from Real Disks' menu option.
  5. Return to step 3 to image more disks.

What does 'Copy Protected' mean?

In order to try and prevent or slow down piracy, many commercial software manufacturers used disk formats that can not be reproduced by a standard Atari disk drive.

By using special tricks their software could verify the disks were not copied by checks for these exotic formats when loaded, and refuse to run if copied.

How do I copy a disk image onto a REAL disk?

The easiest way to convert a disk image to a whole Atari disk is by a process called 'sector copying'. You may have used this method on your Atari to duplicate a real floppy disk.

Method #1: (Using APE or APE'98, the Atari Computer, and a real Atari disk drive)

  1. Load APE and attach your APE interface, being sure to verify it is working.
  2. Attach your real Atari disk drive to the SIO bus, configure it as drive 2.
  3. Turn on the real disk drive.
  4. Load the APE_WARP.ATR image into drive 1. This disk image is included in the APE distribution package.
  5. Boot your Atari from the APE_WARP.ATR image in drive 1.
  6. When the dos-loader menu appears, select the 'MYCOPIER' program.
  7. Once MYCOPIER has loaded, release the APE_WARP.ATR image from drive 1.
  8. Insert the real diskette you want to write to into the real disk drive.
  9. Load the ATR image you want to copy to a real disk into drive 1.
  10. Configure MyCopier with the DESTINATION drive as 2 (real drive), and the SOURCE as drive 1 (disk image).
  11. Press START on the Atari to start the sector copy. Once complete the disk image in drive 2 will be an exact duplicate of the disk image in drive 1.
  12. Return to step 8 to image more disks.

Method #2: (Using the DOS ProSystem and a real Atari disk drive)

  1. Load the ProSystem program on the PC and attach your ProSystem interface. The interface should attach to the PC's serial port on one end, and an Atari disk drive on the other.
  2. Configure the Atari disk drive as drive 1, this is VERY important.
  3. Turn on the Atari disk drive and insert the disk you wish to fill with the ATR image.
  4. To write an ATR image out to a real disk, press 'W' on the PC.
  5. Return to step 3 to write out more disks.

Method #3: (Using ProSystem'98 and a real Atari disk drive)

  1. Load the ProSystem program on the PC and attach your ProSystem interface. The interface should attach to the PC's serial port on one end, and an Atari disk drive on the other.
  2. With the ProSystem'98 software you may attach up to 4 disk drives at once. Each drive must have a unique drive ID, but need not start at drive 1.
  3. Turn on the Atari disk drive(s) and insert the disk(s) you wish to write to. If using more than one drive, insert ALL the disks you wish to write to.
  4. To write-out ATR images, use the 'Write ATR Image(s) to Real Disk(s)' menu option.
  5. Return to step 3 to image more disks.

How do I put my favorite DOS on a disk image?

Atari DOS and Compatibles: Use 'I' to initialize (format) the disk image, then use 'H' to write system files to the disk image.

Spartados: Use XINIT to format the disk and write the dos file as usual.

How do I create a big hard disk sized image?

Create a new blank disk image as usual, except this time select a custom size.

Select 65535 sectors, double density. This will create a 16 megabyte Atari hard disk image. MAKE SURE you have 16MB of free space on the PC to create the new ATR file.

What Atari DOS Systems will support a large hard disk?

Both MyDOS and Spartados will support hard disk images of ANY size up to the maximum size of 16MB per drive.

Atari DOS 2.0, 2.5, 3.0 and clones will NOT read or write to any such image since they are designed for floppy drives only.

How do I format and write DOS to a big hard disk image?

MyDOS 4.X:

  1. Load the new blank hard disk image into drive 2.
  2. Use the 'O' option on the Atari to configure drive 2.
  3. Enter drive 2 as the drive to configure.
  4. Answer no (N) to the question 'Remove Drive'.
  5. Answer yes (Y) to the question 'Is Drive Configurable'.
  6. Answer yes (Y) to the question 'High Capacity Drive'.
  7. Enter the exact number of sectors in the disk image and press return. In the example above this number would be 65535.
  8. Use the 'I' command to format the hard disk image.
  9. Use the 'H' option to write DOS files to the hard disk image. You can now boot DOS from this image and use it as a hard disk.

Spartados:

  1. Load the new blank hard disk image into drive 3.
  2. With the working Spartados image in drive 1, execute the 'HDINIT' program.
  3. Choose to initialize drive 3.
  4. MANUALLY copy the Spartados DOS file to the hard disk image. Example: COPY D1:X32G.DOS D3:X32G.DOS
  5. Change to drive 3 and execute the BOOT command to make the hard disk image bootable. This command takes the name of the DOS file as an argument, for example 'BOOT X32G.DOS' would be used if the DOS file you copied was called X32G.DOS.
  6. The hard disk image is now complete and ready to boot and use.

How do I take a file from my PC's hard disk and put it into a disk image?

To copy a single file off your PC's hard disk into an Atari Disk Image for use by the Atari is a simple matter with APE.

Configure APE's PC-MIRROR drive as drive 1, and set the default path to the drive and path where the file(s) you want to copy reside on your PC's hard disk.

Load the Atari disk image you want to copy the file(s) into in APE's drive 2.

Use your favorite Atari DOS to copy the files from drive 1 (PC) to drive 2 (Atari disk image on PC).

This is possible because APE's PC-MIRROR makes the raw contents of your PC's hard disk look just like an Atari disk, so NO special software is required.

How do I get a file off a disk image and onto my PC's hard drive?

To copy out of an ATR image and onto your PC's hard disk is a simple matter with APE.

Configure APE's PC-MIRROR drive as drive 1, and set the default path to the drive and path where you want the files deposited on your PC.

Load the Atari disk image you want to copy the file(s) from into APE's drive 2.

Use your favorite Atari DOS 2.X compatible DOS to copy the files from drive 2 (ATR) to drive 1 (PC Hard Disk).

This is possible because APE's PC-MIRROR makes the raw contents of your PC's hard disk look just like an Atari disk, so NO special software is required.

You MUST use an Atari 2.0 compatible DOS for this function. Do not use Spartados for this operation.

Copying files from the Atari to the PC in this particular manner requires the registered version of APE.

I have a disk image, how do I boot my Atari from it with APE?

Most disk images you find will be bootable, either to DOS or to the game or application software they contain.

Just load the disk image into APE's drive 1 and turn on the Atari. If your cable connections are good, the Atari will boot right from the PC off the disk image. No special software is required on the Atari.

Technical: How is an ATR file formatted?

The 'standard' ATR file format is: (first byte listed as 1, not 0)

  • 01: NICKATARI Signature
  • 02: "
  • 03: Paragraphs, low
  • 04: Paragraphs, high
  • 05: Sector Size, low
  • 06: Sector Size, high
  • 07: Extended paragraphs
  • 08..16: Unused
  • Remainder of image contains Atari data.

Technical: What extensions to the ATR format does APE provide?

Current APE changes to the ATR header:

  • Byte 8 : 32bit Authentication CRC
  • 9 : 32bit Authentication CRC
  • 10: 32bit Authentication CRC
  • 11: 32bit Authentication CRC

  • 16: Bit 0: Write Protect
    • Bit 1: Sealed/Authenticated Atr
    • Bits 2..7: Unused

ATR Authentication info is available at http://www.atarimax.com/.