Atari ST beginners FAQ and basics
Atari ST was launched in 1985. As next generation (for that time) home/business computer, with GUI (graphical user interface), mouse as standard equipment, floppy drive, hard disk support in HW and OS. Atari ST's OS is called TOS, and consists from 2 main parts: GEMDOS - responsible for boot, HW, disk/file handling. And GEM - graphical environment manager , + Desktop as part of it, where most common tasks can be performed.


Atari's disk operating system is very similar to DOS, what is no wonder, since is developed by Digital Research. So, floppies are using FAT12 filesystem, what was standard already in that time. And Atari/DR made it pretty much flexible - unlike DOS and Windows, format is not rigid, so it will work well with 800 KB floppies, 400 KB (single side) and even 880 KB or little more. In Desktop there is floppy format option, but it can produce only 360 or 720 KB formats. And only at TOS 1.04 it is really DOS compatible (earlier versions had wrong start bytes).
What today (2019) is relevant is that work with floppies is everything but not easy. Mostly because disks and drives are very old, so it is unreliable. Considering access of Atari floppy disks on some PC: that was problem already some 15 years ago, mostly because Windows inflexible floppy driver. And now there are no floppy drives in PCs, and no floppy connector at all, so you can not connect it to newer PC internally. Only way is USB floppy drive, if there are such still in shops. But that way is very limited. Such drives will not work with formats like 800 KB. Some will work with only 1.44 MB format, so pretty much useless.

Hard disks, mass storage with Atari ST family:

There is FAT16 support in TOS, what is just another standard filesystem type. And it is DOS compatible, but only up to 32 MB partition size. Well, such partitions are compatible, but not MBR (master boot record) too - so, DOS, Windows, MAC will not be able to access hard disks, or now rather Flash cards with Atari type (AHDI) partitions. The solution is to use DOS type MBR, and there is nothing bad in it, since TOS self doesn't deal with MBR, that's on hard disk driver SW. + TOS/DOS compatible partitions - and they can be of max size of 512 MB on TOS 1.04 and higher. With 1.00-1.02 max size is 256 MB. Max count of partitions what TOS can handle is 14.
TOS/DOS compatible partitioning means very easy data transfer with some modern computer, especially in case of Flash cards.

What mass storage in 2019 ?

Indeed some Flash card based one. Most popular is UltraSatan - it uses SD cards, speed is good, and is well supported. With IDE adapter can use CF cards, which are now little harder to find, are more expensive.  In any case is recommended to use brand cards, from reliable source. There is lot of crap on market. Cheaper can be just useless.

GEMDOS, Desktop:

Windows, icons, mouse, pull down menus (WIPM) - that's is key of it. Usage is really not hard, and can get familiar in short time. Actually, there is no so big diff. between it and some new OS. Of course, there is much less to learn :-)
Limited choice of features can be expanded with so called Desktop Accessories. They are special programs with extension ACC, and will load automatically from bood drive after power on, reset or resolution change. For instance CONTROL.ACC serves for time setting/read. Setting colors, mouse speed ... Accessories are nice thing, but they eat RAM and may slowdown computer, so use them when it is really needed. Bad practice is to install 'everything available' .
If there is some program with extension PRG in folder in ROOT named AUTO, it will be executed after GEMDOS initialisation, and before GEM start. It is used mostly with games - and most of them doesn't need GEM, so will have more RAM available.
AUTO start is used too, to install some resident SW like diverse drivers, extensions, fonts, etc. Same stays as for accessories - do not install everything, just what really need.

Why it starts not, why need to wait about minute that Desktop appear ?
It needs formatted floppy in drive.

One of most frequent questions is: why I don't see hard disk partitions D, E ... on Desktop ?

TOS 1.xx will put only partition (logical drive) C: icon on Desktop if it is mounted by hard disk driver. Others need to add there 'by hand'
Icon for C: will not appear too, if Desktop is saved without it.
Select one of drives (A, B, C ...), then Options, Install Disk Drive. Type in drive letter (capital) and may give label by wish. Of course Install to finish it .  


To save self from doing it every time again, use Save Desktop option. Options, Save Desktop.
That will save current resolution too, so you may start in medium resolution without need to change.

Atari ST SW compatibility:

Will focus here mostly on games. This is very complex problem, and to judge reliably why some SW, game works not with certain configuration is really hard, and needs lot of experience.

Most common cause of problem(s):  TOS version . Espacially early games, from 1985-87 can have problems on later TOS versions. Like joystick or mouse works not (properly) .
Here need to write little about TOS versions:
1.00 - there is even disk based version of it, so only small part is in ROM, most loads. Pretty much useless, and hard to find such - most is upgraded long time ago. 1.00 is really not recommended, especially with hard disks. There are few games which work only with it, but you can find updated/fixed version of them for higher TOS versions.
For Atari ST TOS 1.04 is recommended. For STE 1.62 (bugfixed 1.06).  There is TOS 2.06, with much better Desktop, and worse compatibility, especially with games. Still, can play a lot, almost all, since quality games are fixed for. But you can not just put TOS 2.06 EPROMs in some ST - it needs little + HW that it work.

Some games will fail on STE, and common cause is TOS version, but there are few with silly bugs (STE is very compatible in HW with ST) - and they are fixed for STE.

Probably most stupid cause is bad code in games considering RAM size in machine: some will crash with 1MB or more, and work only with 512 K. Some will crash with 4MB RAM . The reason is lack of testing - RAM was very expensive in those early years, so even SW developers had no machines with lot of RAM . Most of it is fixed.

Some will not work because regional restrictions - game (SW) code will check for TOS language/region version, and if don't like it, to say so - like region is USA, and SW is intended for Europe, it will simply not work. Usually will write nothing on screen. Because it stays in manual, and pirate copies have no manual :-)

Running Atari ST(E) games from hard disk:

Another complex problem. In short: most of it will not work from hard disk without changes, fixes, and that is work for expert.
Only small count of games has option to install on hard disk, and even then may need original floppy to check is it original or pirate copy. Or just whole hard disk install is obsolete now.
In 2019 we can say that basically all quality games are already adapted for work from hard disk.

Will add here some useful links in next days ...


    PP,   May  2019.