A Hacker's Hard Disk for the Atari ST
A Hacker's Hard Disk for the Atari ST
Tom Love
(c) Copyright 1987, John Thomas Love, Rt. 2, Box 277, Sterling, VA 22170 USA. (703)430-2853
All rights reserved. Reproduction of this document for profit or other business purposes by any means is prohibited without written permission from the author. Permission for not-for-profit electronic distribution of this document is granted providing this copyright notice appears in its entirety. Copies of the graphics referenced in this article are available from the author at the above address for the cost of return postage.
Atari, TOS, and Atari ST are trademarks of Atari Corp. Unix is a registered trademark of AT&T Bell Laboratories. IBM, IBM PC/XT, and IBM PC/AT are registered trademarks of International Business Machines Corp. GEM is a trademark of Digital Research Inc. Supra is a trademark of somebody...
1. Introduction
Back in the old days, when the "home computer" was only beginning to become a reality, the typical computer hobbyist was generally at least as adept at soldering patch wires onto his machine's circuit boards as he was at patching bugs in his code. Since those days personal computing systems have greatly matured, so that most users spend their time using commercial software or perhaps writing programs of their own - but rarely are they actually involved in any sort of hardware hacking.
This article describes the adventures of a relatively hardware-naive user (me) in attempting to assemble a usable hard disk system for an Atari 1040ST using essentially off-the-shelf hardware. The primary goal here is to provide the reader with the sort of documentation I could have used as I muddled through this project. Thus this is not a product review (though no doubt comments of a less than objective nature may sneak in at times); nor is this a "circuit cellar" sort of a project (I never had to use a soldering iron once!). Instead, this a project report, with an emphasis on "how-to" for those considering the same undertaking. But first, some background, to explain the rationale for this project.
The need for a hard disk on my 1040 became obvious very shortly after I brought the system home. I program industrial-strength Unix systems during the day, and am spoiled by the typically huge amounts of online storage available. While I have no doubt that serious software development is possible on floppy-based ST systems, it is not for me. However, the going price for a "turnkey" twenty megabyte hard disk system for the ST is still in excess of $600. This is not only expensive, but provides no reasonable option for upgrading disk storage capacity in the future. Luckily I learned of an alternative approach which solves both problems. This approach employs an industry standard hard disk, controller, and power supply, and a custom board which converts the ST hard disk interface to the interface standard understood by the controller. This custom adaptor board was developed and is sold by Berkeley Microsystems of Oakland, CA., hereafter referred to as "Berkeley".
Since I knew that I could borrow an unused hard disk and power supply from work, the cost of the system immediately became attractive - about $255 for the necessary interface hardware. And expandability with the Berkeley approach is better than with the Supra or Atari hard disks, as the adaptor/controller pair is capable of supporting two separate hard disks simultaneously. The clincher, for me, was the inclusion of a battery backed system clock on the adaptor board, providing the same capabilities as cartridge based clocks which sell for about $50. The only obstacle, as I was informed by Chris Rhodin of Berkeley: no documentation (though he says they will be shipping documentation with their board kits soon). This important consideration notwithstanding, I decided to go for it.
2. System Hardware
The package I received from Berkeley contained an Adaptek SCSI (Small Computer Systems Interface) disk controller board, the Berkeley DMA-to-SCSI adaptor board, four cables, and a microfloppy containing the installation and driver software. Just as promised, there wasn't a scrap of documentation in the box or on the disk. Berkeley left it to me to acquire my own hard disk and power supply. Fig. 1 diagrams the components of the system and how they interconnect logically.
The purpose of the SCSI controller board is twofold. It communicates with the disk drive itself, sending out commands to read and write data, and receiving the results of those commands; and it communicates with the outside world, receiving similar commands and sending back data and status. The controller effectively serves as a protocol converter between the industry standard SCSI protocol and the ST506/ST412 protocol understood by the disk drive.
In many computer systems the "outside world" which drives the disk controller is the system CPU and operating system, often communicating directly on the system bus. In the case of the Atari ST, however, no direct mechanism is provided to interface a disk controller to the CPU, so the CPU communicates with the hard disk by the only reasonably speedy interface provided, the DMA (Direct Memory Access) interface. This external 19 pin interface permits 8-bit parallel communication with the system data bus at rates up to 1 megabyte per second. The intermediary between the DMA interface and the SCSI controller is Berkeley Microsystems' SCSI adaptor board. This adaptor board is responsible for converting between the DMA protocol spoken by the Atari and the SCSI protocol understood by the disk controller.
The disk drive need meet only one requirement: it must be ST506/ST412 compatible. This covers just about all fixed disks manufactured for personal computers since the early Eighties, including drives for the IBM PC/XT and PC/AT and compatibles. Capacities of available drives typically range from 10 megabytes to 86 megabytes; note however that constraints imposed by TOS limit usable capacity of a single drive to 64 megabytes. New 20 megabyte drives (e.g. the Seagate ST225) are typically available for somewhere around $280 without a controller (be sure you do not pay for a controller board, since most are for PCs and are useless to an Atari owner). Alternatively, good deals may be found in new and used hard drives at computer swap meets, in user group magazines, and by word of mouth. Expect to pay on the order of $10 per megabyte for used hardware. The disk I am using is a Quantum 540 which provides 34 megabytes of storage after formatting.
Acquisition of a power supply is a similar problem. New power supplies for PCs are available from discount houses for $50 to $75, depending on power output rating. Alternatively, scrounging might net you just what you need for twenty dollars or less. If buying a PC-type power supply, plan on buying one with a minimum of of 65 watts output for a single hard drive system or 135 watts for a double drive system. If you're scrounging, keep in mind that you need +5 volt and +12 volt output, with 3 to 5 amps each for a single drive system and 6 to 10 amps each for a double drive system. Different hard drives have different power requirements, so if possible consult the drive's technical reference manual for peak power draw. It is a good idea to put an AC line filter on the 110V input to the power supply, and a line switch on the input is highly recommended for turning the disk system on and off. The power is distributed to each of the boards and to each disk drive by means of four wires and a standard keyed AMP "Mate-N-Lok" connector, identical to that used by conventional floppy drives and available at any electronics supply house (AMP part number 1-408424-0). Most PC power supplies come with harnesses and connectors ready-made.
Finally, the cables. Berkeley can provide cables for a single drive system for a minimal cost. Their cable kit includes the 19 wire cable between the DMA port and their adaptor board; a short flat 50 wire ribbon cable to connect the Berkeley adaptor to the Adaptek controller; and two flat ribbon cables to connect the controller to the hard drive, a 20 wire data cable and a 34 wire control cable. If a second hard drive is used a third connector should be crimped onto the middle of the control cable, and second data cable is necessary. If you have access to facilities for manufacturing your own cables you might be well advised to, since the cables provided by Berkeley are painfully short. My installation uses the cables provided by Berkeley, though, so it is possible.
3. Hardware Assembly
Before beginning assembly we need to consider how this package is to be enclosed, if at all. Things to think about are RF emissions, heat dissipation, isolation from external disturbances, and general tidiness. The boards and drive do not seem to emit any noticable RF (radio frequency) noise, so unless you live in a neighborhood of ham radio fanatics you probably do not need to go to the trouble or expense of a metal enclosure. My setup seemed to run a little warm at first, but since my power supply happens to have a built-in fan I just rearranged things so that the power supply cools the other components. If necessary, a muffin fan can be added to the setup for about $10.
I opted for the "cheap-is-beautiful" approach, sandwiching the two boards between two 6" by 8" pieces of 1/4" plywood, holding the whole thing together with four 4" long #6 machine screws and spacing each layer by about 3/4 of an inch with nuts and small pieces of non-conductive plastic tubing. The hard drive sits on top of the whole sandwich. Crude but simple. It is also possible to screw the boards directly to the bottom of the hard drive, or use commercially available mounting rails.
My assembly method was largely dictated by the short cables provided by Berkeley. After playing with the connectors it became apparent that there was only one way things would fit together. Figure 2 graphically illustrates this connectivity; the following paragraphs provide a more detailed explanation.
Begin with the assumption that the circuitry attached to your hard drive is the on the bottom. The disk controller board goes directly underneath the hard drive, with the components facing down and the 50 pin header (the two rows of pins sticking straight out from the board) and LED toward the front. Under the controller goes the Berkeley adaptor board, with its components also facing down and its 50 pin header toward the front. The 19 wire DMA cable connects to the header on the back side of the Berkeley adaptor board, with the cable directed away from the board. Next the 50 wire ribbon cable connects the 50 pin headers on the front of both boards. Proper orientation is important. This is achieved by plugging the cable into the Adaptek so it that it extends away from the board (toward the front), then bending it down and flipping the connector around so that it meets the Berkeley adaptor board's header.
Next, the disk drive is connected to the controller by the 20 wire data cable and the 34 wire control cable. These cables attach to the disk drive by means of edge connectors; on the disk controller the control cable attaches with an edge connector while the data cable(s) attach to the header(s) at the rear of the board. The header near the side of the board is used for drive zero (the designation for the drive in a single-drive system, or the first drive in a two-drive system); the header in the middle of the back of the controller is used for drive one in a two-drive system. The control cable attaches directly without any twists. The data cable is attached to the disk with the cable directed downward, and is turned under to fasten to the appropriate header on the bottom of the controller. Note that none of the ribbon cables used require any twists in them.
One further consideration: hard drives typically have a jumper on the bottom labelled "DS". This is the "drive select" jumper which provides each disk with an identity, whether drive zero, drive one, or greater. On a single drive system the DS jumper should be set to 0; on a double drive system one disk should be set to DS0 and the other to DS1.
Finally, power connectors need to be supplied to each of the boards and the disk drive. The standard connector keying makes this straightforward. Now comes the test of nerve: plug it into the wall and turn it on (for safety's sake while disconnected from the ST's DMA port). If everything was put together properly the LEDs on the disk controller and drive will begin blinking and you will hear the unmistakeable sound of the hard drive beginning to spin and coming up to speed. If these things do not happen all I can suggest is re-reading everything above and trying again before calling Berkeley.
4. Software Installation and Configuration
In order to make the disk usable to the ST it must be properly installed and formatted. Begin this procedure by turning everything off, connecting the DMA cable to the back of the ST, turning on the hard drive, and then after it is spun up turning on the ST. Insert the floppy supplied by Berkeley into drive A and open it up.
The AUTO folder on the Berkeley disk contains two programs, install.prg and setclk.prg. These should both copied into the AUTO folder on your boot floppy. Install.prg handles boot-time installation of the hard disk, and setclk.prg automatically notifies GEM of the date and time stored in the clock on the adaptor board. The battery-backed clock needs to be set once at installation time. This is done by setting the date and time correctly in the GEM Control Panel and then running the program initclk.prg in the root directory of the Berkeley floppy. This program only need be run again when the hardware clock needs to be reset, for example when changing to daylight savings time, leap year, or if the battery wears out.
Next open up the AHDI folder on the diskette. This contains two programs of interest, hdx.prg and ship.prg, and an important data file called wincap. Hdx is the hard disk installer program, and ship is used for parking the disk's heads before transportation. The wincap file needs to be examined to ensure that it contains data relevant to your brand and model of disk drive, including the name, the number of heads, the number of cylinders, write precompensation, reduced write current, default partition, and other obscure things. Wincap entries for a number of the more standard drives are already in place. If your drive is not one of the ones already installed you will need to refer to a technical reference manual for your drive, Chris at Berkeley Microsystems, or both in order to get a usable entry. A text editor such as micro-emacs is necessary to modify the wincap file.
Next run the program hdx.prg. This is a GEM application which is used to format, partition, zero, and mark bad blocks on the disk. Each operation is available under the "DISK" pulldown menu. The format operation should be performed first, so pull down and activate "format". You must verify that you want to format, then select the physical unit. This will be drive 0. Next you must pick the drive type from a menu which is generated based on the wincap file. Finally, you must verify one more time that you want to format (an operation which destroys all data on the disk), and formatting will begin.
The next step is to partition. Again you must verify that you wish to partition and name the physical unit, then you are presented with a panel of logical unit names (C: through P:) with sizes associated with each partition. A partition, or logical unit, may be no larger than 16 megabytes. You may divide up your disk as you like; mine is cut into 14, 10, and 10 megabytes for C: through E: respectively. If you have a favorite ramdisk which is hardcoded to be device C: (or something else) you may wish to partition around it.
Next each partition must be zeroed. Invoke the "zero" step once for each partition, specifying which partition each time. And last invoke the "markbad" step once for each partition. This scans through each partition identifying and mapping out unreliable blocks; it takes longer than any of the other steps. When all this is done, exit hdx by pulling down the FILE menu and activating "quit".
The last step is to establish an icon for each partition by selecting an existing disk icon and choosing "install disk drive" from the OPTIONS menu, filling out the drive identifier and icon label fields, and clicking on "install". This should be done once for each partition built in the hdx partition step. When this is done, save your desktop to your boot floppy and try powering everything down and cold booting. If the installation went properly, your desktop will show an icon for each partition. Select each icon one at a time and "show info" to verify that the correct amount of bytes available is displayed. If all this appears right, consider yourself the owner of a hard disk system.
5. Use
Use of a hard disk in the TOS environment is not much different than use of floppy disks, except of course that the hard disk is much bigger, faster, and does not require any of that obnoxious disk swapping. At this time a boot floppy containing your AUTO folder, desktop.inf, and any desired desk accessories is still necessary; both Atari and Berkeley Microsystems are working on reliable methods for booting directly from the hard disk.
When turning on your system you should turn on your power supply first, powering up the boards and disk. Turn on the monitor while waiting for the the disk to spin up. After about five or ten seconds, when the disk is spun up and its LED stops blinking, then turn on the ST. In powering down, reverse the order: ST off first, disk last. Note that cycling power on the disk while the system is up causes a system reset.
Installing a hard disk may solve many problems, but it invariably introduces one rather unpleasant one: backing up your files. I am unaware of any reasonably priced tape backup mechanism currently or soon available for the ST. This leaves the floppy as the only viable medium. There are a variety of commercial and public domain packages available to make the procedure easier and faster than simply copying.
One issue which has not been received much press but is very important to all ST users is what has come to be known as the "forty folder limit". Due to a bug in GEMDOS's limited resource manager, the TOS file system can get a case of amnesia if more than forty folders exist on the set of installed partitions (including the floppy). The problem does not occur every time, but if it does, the loss of information on your hard disk may be total. Therefore until a fix is published by Atari you should keep a close watch on the number of folders you create on your filesystem.
6. Evaluation, Conclusions, and Recommendations
If you have read through all of the above installation instructions you may have come to the conclusion that all this is a lot of trouble; if so, you're not far wrong. However, for some people this "hacker's" hard disk makes more sense than the expensive turnkey systems. These people would be those with inexpensive access to any of the components of the system; those with limited budgets who want to start out small (say with a cheap 10 meg disk) and later expand; those with very large storage needs such as BBS sysops, programmers, and businesses; and those who just like to tinker with hardware. I would specifically not recommend this system to those meek people who are obsessed with warranties or have a deathly fear of electricity.
My system has operated reliably since I put it on line several weeks ago. While I cannot provide any quantitative data as to performance or contrast my system with an Atari or Supra hard disk, loading software is significantly, perhaps five to eight times, faster than loading from floppy. Overall it has greatly improved the utility of my system and at an exceptionally low cost.
Postscript: The address for Berkeley Microsystems is: 1107 El Centro Ave., Oakland, CA USA 94602, phone (415)530-3436.
The price for the two-board set is still $250 but will be going up, so contact Berkeley Microsystems to verify price information before ordering. Berkeley will be shipping an installation manual with their boards soon.
