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Where can I learn more about ATR files?

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Sorry for the newbie questions. I just cannot believe all of the advances made in the Atari world in the 30+ years I was gone.



From what I gather, an atr file is sort of like a virtual disk image of the old diskette? I would like to know things like how to get files into an atr file. How to get them out. But I think I found a post in the newbie thread on that.


Who came up with the standard? How long has it been around? Is there a file stucture documented somewhere? Stuff like that. ;)


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If you want to get individual files on/off .atr images, Altirra can do that easily (although some DOS versions don't always work)


To extract a file off an .atr, use the 'Tools->Disk Explore

Browse to your image file and it will give you the directory listing in that .atr, simply drag and drop any files to a Windows folder


To put files into an .atr, first create a folder and put your files in here.

Under File->Disk Drives click on the > and select Mount Folder as DOS2 or SpatraDOS and browse to the folder you created and put your files in


You can only read from this folder, so boot the .atr you want the files in and simple copy the files using DOS.

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Wasn't Nick Kennedy (author of SIO2PC hardware and software) the one who invented the ATR format ?!? At that time, several formats for A8 disk images existed, e.g. XFD (Xformer image), DI (XL-Deejay image), DCM/DC3 (Disk-Communicator 3 image), SCP/SCO (SpartaDOS Scopy image), DSK (various programs), etc. Here in Germany we also had magazines with type-in listings to connect our A8 to other computers (e.g. Happy Computer magazine which had programs to connect the A8 with C64 or Atari ST and maybe other computers) and they sold some commercial hardware like PC-link and ST-link to connect the A8 to these computers and exchange files or data...


If you search for the SIO2PC docs, you will surely find everything about the details of ATR images.


ATR became the de-facto standard for unprotected A8 disk images and if you set file associations in your PC OS, double-clicking an ATR image will start the required emulator or tool to execute this image or start analyzing it. Afaik, for protected A8 disk images there is no standard yet, there exist ATX, PRO, SCP and maybe other formats. For tape images we do have .CAS, double-clicking them does start the associated emulator, but it seems they are not automatically executed (I have to do some manual work then, like holding Start or Start+Option while hitting Reset, then hitting the return key, etc. to start loading them)...


ATR file structure (copied from Nick Kennedy's page, see link above):

What is the structure of an ATR disk file?


There is first a 16 byte header with the following information:

WORD = special code* indicating this is an Atari disk file

WORD = size of this disk image, in paragraphs (size/16)

WORD = sector size. (128 or 256) bytes/sector

WORD = high part of size, in paragraphs (added by REV 3.00)

BYTE = disk flags such as copy protection and write protect; see below:

The 9th byte of the header contains information in individual bits. Bit 4 = 1 means the disk image is treated as copy protected (has bad sectors). Bit 5 = 1 means the disk is write protected.

WORD=1st (or typical) bad sector; see below:

The 10th and 11th bytes of the header are a word which contains the number of the first (or of a typical) bad sector. What I mean by typical is that it does contain both bad sector status and good sector status. See the section in README.TXT or in 1050.TXT on copy protection emulation to learn what goes in those sectors.

SPARES 5 unused (spare) header bytes (contain zeroes)

After the header comes the disk image. This is just a continuous string of bytes, with the first 128 bytes being the contents of disk sector 1, the second being sector 2, etc.

* The "code" is the 16 bit sum of the individual ASCII values of the string of bytes: "NICKATARI". If you try to load a file without this first WORD, you get a "THIS FILE IS NOT AN ATARI DISK FILE" error message. Try it.



There is also the A8FAQ which gives some information about ATR and other image formats and some useful links: ftp://rtfm.mit.edu/pub/faqs/atari-8-bit/faq

(subjects 9.1 and also 10.1 and 10.2)

Edited by CharlieChaplin
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Yes, CC I do believe it was all Nick.


Nick Kennedy's site.



In Windows I like to use ATRUtil




Download the zip, extract and put the executable in

the Windows/System32 folder. Make a shorcut to it as

soon as you drop it in there. Rename the shortcut without

the .exe and copy that to the SendTo folder. Right click

an .ATR file and choose to send it to ATRUtil and you

can remove files from it or put others into the image

file. I like it quite a bit and there are several that

do the same.


This program will also take a simple executable and

turn it into a bootable ATR file famously known as a

KBOOT disk. K for Ken Siders, the author, as the screen

image while booting shows a lone K in the corner.

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