3. Hardware


3.1 How can I upgrade memory on my Atari ?

If your ST is equipped with SIMM memory, you can easily upgrade your memory to 1, 2 or 4Mb by just taking out the old SIMMs and popping in the new ones.

The correct memory type is 30 pin SIMMs, with or without parity, capacity being either 256Kb or 1Mb. The minimum speed of 256Kb SIMMs is 150ns and 120ns for 1Mb SIMMs. It is best not to mix different SIMM types. They must be installed by pairs in slots 1 and 3, then 2 and 4 (from back to front).

Atari STEs are originally equipped with either 2 (520STE) or 4 (1040STE) 256Kb SIMMs that can be replaced by 2 or 4 x 1Mb SIMMs.

Because of a bug in TOS, STEs will not recognize a 2.5Mb configuration (2x256Kb + 2x1Mb) without a small bootup program like silkboot2e or simmfix. These can be found on most FTP sites (see section 2.2.3), but are quite unreliable.

On DRAM memory models, the memory chips are soldered directly to the computer's motherboard. This makes memory expansion a lot more tricky.

A way to avoid the soldering and memory limitations is to use a special memory expansion board that replaces the original memory banks with standard SIMM sockets. There are several such solutions available like the Marpet Xtra Ram board or the Aixit 10Mb expansion board. Look for Atari related companies on the Atari web pages (see section 4.3).

DIY conversions require serious soldering skills, and are not for the faint hearted. Descriptions of such modifications can be found below:

On ST, STF and STE computers, the MMU (Memory Management Unit) has a hardware limit of 4Mb.

However recent developments have seen third party expansion boards that allow going beyond this limit. The Magnum-ST board from Woller+Link in Germany allows up to 16Mb on a plain ST/STF (not STE). TOS versions below 2.06 will not deal with more than 4Mb, so either a TOS upgrade or MagiC (see section 2.5) is necessary.

Woller + Link

The step forward from DRAM to SIMMs on the STE series became a step back to a proprietary memory board system on the Falcon. The falcon was pre- equipped with 3 memory board models: 1, 4 or 14Mb. Upgrading a Falcon means scrapping the original memory and replacing it with either a new proprietary memory board or a third party SIMM board. There are many of these available and can sometimes be combined with a CPU accelerator board.

3.2 How can I connect a hard disk drive to my ST ?

ACSI is Atari's proprietary hard drive connector. It is similar to SCSI which was standardized later, but not directly compatible. ACSI drives were the Atari Megafile and SH series that ranged from 20 to 60Mb capacities. Supra, and maybe some other manufacturers also made some ACSI drives at one point, but these are quite rare.

These are the only hard drives that are directly "plug'n'play" compatible with the Atari ACSI/DMA port on stock STs.

Atari SH drives have the advantage of being made up of an ACSI to SCSI host adapter connected to an Adaptec 4000 SCSI to MFM adapter that is attached to the drive. It is therefore sometimes possible to adapt these drive to use SCSI drive mechanisms. This is not the case for Megafile drives.

It is possible to expand Megafile drives by adding a second drive mechanism inside the case. Here are explanations on how to do this:

In order to use SCSI peripherals, and unless you have an internal Atari interface (Mega ST, Mega STe) you need a SCSI host adapter that connects the SCSI drive to the ACSI hard drive port on the Atari. There are several models available depending on whether or not you need parity, whether or not they are for external or internal drives. The 2 most common SCSI host adapters are ICD's The Link II and Link'97 from WB Systemtechnik. Don't forget also that there is not much room for a 3.5" hard drive inside an original ST case. You will need either to put the whole system into a PC type tower case, or to find an external housing and power supply for your hard drive.

The largest drives the Mega STE internal SCSI interface supports are 1Gb. Anything beyond that will be wasted. This interface also does not support parity, therefore you should disable it by using the jumpers on the drive.

A parity generator for any host adapter that does not natively support parity can be easily built by following the instructions below:

There are now at least 3 IDE host adapter boards available. The TUS IDEal board is for STE only, It plugs into the processor socket and requires 4 wires to be soldered to the board. It is mainly aimed at connecting 2.5" IDE drives internally, but 3.5" drives can be attached to it if the computer is tower-mounted.

Mario Becroft's adapter is quite similar but is available for both STF or STE models and includes a TOS 2.06 upgrade, which is required if you plan on booting on the IDE drive.

Instructions to build your own DIY interface also exist, but should only be performed by people with a solid knowledge in electronics, soldering and programming GAL chips.

The Falcon has an internal IDE slot for internal 2.5" IDE drives. Some Falcon users have managed to fit a replacement 3.5" drive after cutting parts of the metallic shielding.

Just a general note: You can partition IDE drives as much as you like, but do not format them. Some of them will not recover from a "low level" format.

Using a parallel ZIP drive on any Atari computer's parallel port is impossible because of the lack of several signals in Atari's implementation of the parallel port. You should use a SCSI ZIP drive. There is however a parallel port interface that plugs into the cartridge port of Atari computers, available from Woller+Link (Germany). SCSI versions of ZIPs and CD-ROMS are recommended, so that you can use a SCSI host adapter (as described in section 3.2.2).

Be aware also that CD ROMS and ZIP drives use parity, so you must have a parity enabled SCSI adapter or perform the following modification to allow parity on a non-parity host adapter:

MFM or RLL drives will need an MFM or RLL to SCSI interface, that you will then connect to the standard SCSI/ACSI host adapter (section 3.2.2) in turn connected to the ST.

In order to get TOS to recognize the drive, a HD driver package will be needed. Here are some of the more popular packages: It also seems that some drivers are more suited to one type of drive whereas they can have problems with other drives. A good idea might be to ask the newsgroups or the software vendor for any compatibility issues before buying.

3.3 Floppy Drives?

The disk drives used by Atari ST computers are industry standard 360K or 720K double-density floppy drives, exactly the same as those in PCs... at least in those days.

PC drives can be used as replacement drives, only nowadays it is difficult to find 720K drives. You can however use just about any 1.44Mb HD drive as these will perform perfectly well in DD 720K mode. Nevertheless, you have to be aware of the following:

Using a high density drive in high density mode on an ST, is feasible, but requires a few hardware hacks, both on the ST and on the drive. Ready made HD kits are available at several places, and a few DIY text files describe (sometimes contradictory) modifications too on several FTP servers. Then there is the issue of the controller chip. The WD-1772 is not designed for handling the faster frequency needed to use HD mode, although some people have had one running for years with no problem so an 'Ajax' chip is highly recommended. Most STEs seem to have an Ajax chip fitted as standard.

All the above modifications are also valid if you are planning on upgrading an external drive. You will still have to modify the drive mechanism, and you will still have to modify the ST's motherboard.

Lots of information on the subject can be found at the following page too:

The Atari Hardware Hack Page

3.4 What about printers ?

All Atari computers have a standard bidirectionnal printer port, which means that basically any printer that connects to a PC parallel port should work with an ST, with the same cable.

A problem lies, however, with the recent appearance of cheap printers "Optimized for Windows 95". These units actually lack hardware, making them rely on require Windows95 to run. They will also not work with a Mac or Unix box, so be careful when you buy.

Atari became famous in the DTP for offering the first cheap laser printers. This was done by using the computer's RAM instead of having built-in memory. The SLM laser printers therefore require at least 2Mb of RAM to run. They also attach to the ACSI/DMA port, which means that they cannot be connected to a Falcon. A Falcon/SLM adapter, called the Heatseaker, did exist but never got to the market.

The issue of printer drivers is mainly an application problem. The part of TOS originally devoted to printing and graphic output, called GDOS, was not included in ROM, therefore some applications bypassed it and developed their own printing routines. This sort of application will require it's own proper drivers to be written.

Properly written programs will use the GDOS standard, allowing use of proportionnal fonts and standard drivers.

To run GDOS on your computer, there are several solutions. FontGDOS is the latest freeware GDOS implementation from Atari, but is slow and handles only bitmap fonts. SpeedoGDOS and NVDI are both commercially available and fully maintained, and handle both bitmap and proportional fonts. NVDI is also a very efficient screen accelerator. Basically, if you plan on using a printer, you should consider obtaining NVDI.

3.5 Mouse and Keyboard

The Atari mouse was quite poor, and very few remain in good working condition after the years. When it finally needs replacing, these mice are very hard to find. Try contacting an Atari dealer in your area, as most of them carry some sort of Atari compatible mouse.

A PC serial mouse can be connected directly to the serial (modem) port. There are two drawbacks to this. Firstly, on a machine with only one serial port it prevents from connecting anything else (modem, extra midi ports...). Secondly, you will need to load a serial mouse driver such as Genmouse, which can be found on your favourite FTP sites (see section 2.2.3). The problem is that, being an auto folder program, it will obviously not run with autobooting programs such as games.

A PC mouse can be attached to the Atari mouse connector, but this needs a complicated adapter board, such as those described here:

Some Amiga mice have a little Amiga/ST switch allowing them to be used on an Atari, the only difference between the two being two swapped wires.

Although old PC Bus mice are now probably as difficult to get as ST mice, instructions on adapting one for use on an Atari can be found here:

If all else fails, you can always use the Alt + Arrow keys trick (Alt + Shift + Arrow keys for pixel scale movement, Alt+Clr/Home for left click, and Alt+Insert for right click) as a lifesaver, but that's hardly a practical solution in the long run.

Erratic mouse behaviour is sometimes caused by a faulty connector. The mouse port connections under the keyboard, are subject to stress when there is continuous plugging and unplugging of the mouse (to connect a joystick for example). A remedy for this is to take apart the ST and touch the solder joints that connect the mouse connector to the keyboard PCB with a soldering iron, just to restablish a good contact by slightly melting the solder.

One of the weak points of the Atari ST is the keyboard. First of all, the standard ST/STF/STE/Falcon has a very "squishy" touch. There are solutions to this, such as the famous "TT keys" rubber cups that you are supposed to put under each key to give it a more pleasant feel.

The Mega ST,Mega STE and TT keyboards were much more professional and can be easily adapted to the other machines. For this, but also because the best way to repair a broken keyboard is to just replace it, you might want to follow the instructions below.

It is also possible to attach a PC keyboard to the Atari, in case you want to adapt it to a tower case. There are several such adapters around, like Mario Becroft's one

3.6 The Universal 4 Inch Drop Fix(tm).

A common problem on Atari ST computers is socketed chip connections coming loose. The symptoms are erratic behaviour, sudden resets, unexpected bombs, blank screen (white), disk errors, etc... This is the result of the PCB aging, heating, dilating, warping, slowly easing the chips out of there sockets.

A common, and quick fix to this is the famous 4 inch drop, and it goes like this:

As silly as it may sound, this sometimes works, reseating the chips and solving the problem. The result is not 100% guaranteed however. If the problem still occurs you probably have a more serious problem.

Of course, another (more professional) option is to take apart the machine and reseat all the chips by hand.

3.7 Schematics and Connector Pinouts.

When your computer breaks and there is no Atari Service Center in your neighbourhood to repair it for you, you'll want to see if you can do it yourself, or get someone else to fix it. Chances are that you will need some schematics of the machine. You can find most of these at the following addresses:
Schematics Mania
Schematics of one of the many power supply units that shipped with the ST machines can be found here:
Many people ask for information about the Atari proprietary port pinouts. These can be found in the computer manual, but if you don't have one around, this page has pinout information for just about any connector in the electronics industry, including all the Atari ports, standard VGA connectors and SCART/Peritel sockets. Full plans of an ST monitor port to VGA monitor adapter can be downloaded from here:

Atari ST Quick FAQ - v2.9a - bales@online.fr