Hard disk management

zeST supports the emulation of ACSI hard disks. It also allows setting up a “GEMDOS drive”.

Hard disks are materialised by image files, which contain the raw disk content. Just like any physical disk, image files may contain multiple partitions, which can be formatted using any desired filesystem, however the usual filesystem on Atari TOS is DOS. zeST supports using up to 8 disk image files simultaneously.

Image files are raw binary files whose file names have a .img extension.

The GEMDOS drive allows you to map a directory in the Linux system as a virtual disk unit on the Atari.

From the zeST menu, in the Hard disks submenu, you can choose the image files for the different ACSI IDs (0 to 7), as well as define the directory that will be mapped as the GEMDOS drive.

You can “unplug” a disk by highlighting the corresponding menu entry then pressing Delete or Backspace.

Hard disk image installation

There are different ways of getting started with disk image files.

From an emulator

Software emulators such as Hatari or Steem SSE also support disk image files. You can copy the image files you are using directly to your zeST SD card. Just make sure their file name have a .img extension.

Creating a blank disk image

From the Linux command line, you can directly create a blank file of any size on the SD card with the command:

cd /sdcard
dd of=file.img count=0 bs=1M seek=<size-in-MiB>

This file can then be mounted in zeST; then you will have to partition it using your favourite disk driver's partitioning utility.

Creating a new, partitioned and formatted drive

zeST embeds a make-hdd-image disk image creation, partitioning and formatting script that you can use from the Linux command line.

This script can create an image file containing one or more formatted partitions.

The script arguments are the name of the new file to be created, and the list of sizes, in MiB (1024*1024 bytes) of the different partitions to create. The image file size is then the sum of all partitions sizes.

For instance, to create a disk image with partitions of 32, 60 and 90 MiB, type the commands:

cd /sdcard
make-hdd-image file.img 32 60 90

Note that if the first partition size is lower or equal to 32 megabytes, it will be formatted in an Atari-specific, AHDI-compatible way.

The GEMDOS drive

The GEMDOS drive allows you to define a directory in the Linux system whose contained files will be present as a disk drive on the Atari system. This way, files are directly accessible both on Linux and the Atari, making file exchange easier between systems, allowing the use of networked drives, etc. It is an alternative to using disk image files.

The GEMDOS drive is materialised as a specific ACSI drive unit, that will use the first ACSI ID that is not assigned to a disk image file.

It requires a specific driver to work, that is called the GEMDOS drive stub. This driver is automatically executed when the GEMDOS drive is set as the boot drive, or can be placed on your boot drive's AUTO folder.

Limitations

The GEMDOS drive requires a system ROM that implements a version of GEMDOS superior or equal to 0.15. This excludes TOS versions 1.00 and 1.02. The driver will crash on these versions. It will work fine on TOS versions 1.04 and 2.06.

EmuTOS is also supported. However, on current versions, it does not allow to use the GEMDOS drive as the boot device. You can still boot on a regular hard disk or floppy image, on which you installed zeST's GEMDOS stub program in the AUTO folder. The GEMDOS drive will be assigned the first unused drive letter following the existing installed partitions.

Booting on the GEMDOS drive

The GEMDOS drive is a special ACSI bootable device. It will actually boot when the following conditions are fulfilled:

  • zeST is using a ROM that supports booting on ACSI drives. This excludes EmuTOS that uses its own disk driver and does not run bootsectors.
  • There are no bootable drives assigned to ACSI IDs prior to the first unassigned one. The simplest, safest way is to not assign a HDD image file to ACSI ID 0, so the GEMDOS drive will use ID 0 and will be the first bootable drive.

File name restrictions

The zeST GEMDOS drive rules for file naming are rather straightforward:

  • File names must respect the 8.3 DOS name formatting. Files whose names do not respect this formatting are ignored and will not be visible on the Atari.
  • No restrictions in lower/upper case names. New files will be created with a name in lower case.
  • If two different files have names that map to the same upper case name, only one of them will be accessible on the Atari.
  • Not being a restriction per se, but in the current state of the implementation it is safer to avoid non-ASCII characters in file names.