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Accessing OS/2 Stacker Compressed Diskettes

Technical Blog Post


Accessing OS/2 Stacker Compressed Diskettes


Back in Februray, my blog post [A Box Full of Floppies] mentioned that I uncovered some diskettes compressed with OS/2 Stacker. Jokingly, I suggested that I may have to stand up an OS/2 machine just to check out what is actually on those floppies. Each floppy contains only three files: README.STC, STACKER.EXE and a hidden STACKVOL.DSK file. The README.STC explains that the disk is compressed by Stacker, a program developed by [Stac Electronics, Inc.]. The STACKER.EXE would not run on Windows XP, Vista or Windows 7. The STACKVOL.DSK is just a huge binary file, like a ZIP file, compressed with [Lempel-Ziv-Stac] algorithm that combines Lempel-Ziv with Huffman coding.

In my follow-up post [Like Sands in an Hourglass], I explained how there are many ways I could have tackled this project. I could either use the Emulation approach and try to build an OS/2 guest image under a hypervisor like VMware, KVM or VirtualBox, or just take the Museum approach and try taking one of my half dozen old machines, wipe it clean and stand up OS/2 on it bare metal. This turned out to be more challenging than I expected. The systems I have that are modern and powerful enough to run hypervisors don't have floppy drives, so I opted for the Museum approach.

(A quick [history of OS/2] might be helpful. IBM and Microsoft jointly developed OS/2 back in 1985. By 1990, Microsoft decided it's own Windows operating system was more popular with the ladies, and decided to break off with IBM. In 1992, IBM release OS/2 version 2.0, touted as "a better DOS than DOS and a better Windows than Windows!" Both parties maintained ownership rights, Microsoft renamed OS/2 to Windows NT. The "NT" stood for New Technology, the basis for all of the enterprise-class Windows servers used today. IBM named its version of OS/2 version 3 and 4 "WARP", with the last version 4.52 released in 2001. In its heyday, OS/2 ran the majority of Automated Teller Machines (ATMs), was used for hardware management consoles (HMC), and was used worldwide to run various Railway systems. After 2001, IBM encouraged people to transition from Windows or OS/2 over to Java and Linux. For those that can't or won't leave OS/2, IBM partnered with Serenity Systems to continue OS/2 under the brand [eComStation].)

Working with an IBM [ThinkCentre 8195-E2U Pentium 4 machine] with 640MB RAM and 80GB hard disk, a CD-rom and one 3.5-inch floppy drive, I first discovered that OS/2 is limited to very small amounts of hard disk. There are limits on [file systems and partition sizes] as well as the infamous [1024-cylinder limit] for bootable operating systems. Having a completely empty drive didn't work, as the size of the disk was too big. Carving out a big partition out of this also failed, as it exceeded the various limits. Each time, it felt the partition table was corrupted because the values were so huge. Even modern Disk Partitioning tools ([SysRescueCD] or [PartedMagic]) didn't work, as these create partitions not recognizable to OS/2.

OS/2 Installation Diskettes

The next obstacle I knew I would encounter would be device drivers. OS/2 comes as a set of three floppy diskettes and a CD-rom. The bootable installation disk was referred to affectionately as "Disk 0", then Disk 1, then Disk 2. Once all drivers have been loaded into memory, then it can start looking at the CDrom, and continue with the installation. In searching for updated drivers, I came across [Updated OS/2 Warp 4 Installation Diskettes] to address problems with newer display monitors. It also addresses the 8.4GB volume limit.

The updates were in the form of EXE files that only execute in a running DOS or OS/2 environment, expanded onto a floppy diskette. It seemed like [Catch-22], I need a working DOS or OS/2 system to run the update programs to create the diskettes, but need the diskettes to build a working system.


To get around this, I decided to take a "scaffolding" approach. Using DOS 6 bootable floppy, I was able to re-partition the drive with FDISK into two small 1.9GB partitions. I have the full five-floppy IBM DOS 6 set, I hid the first partition for OS/2, and install the DOS 6 GUI on the second partition. I went ahead and added a few new subdirectories: BOOT to hold Grub2, PERSONAL to hold the data I decompress from the floppies, and UTILS to hold additional utilities. This little DOS system worked, and I now have new OS/2 "Disk 1" and "Disk 2" for the installation process.

(If you don't have a full set of DOS installation diskettes, you can make due with "FORMAT C: /S" from a [DOS boot disk], and then just copy over all the files from the boot disk to your C: drive. You won't have a nice DOS GUI, but the command line prompt will be enough to proceed.)

Like DOS, OS/2 expects to be installed on the C: drive. I hid the second partition (DOS), and marked the first partition installable and bootable. The OS/2 installation involves a lot of reboots, and the hard drive is not natively bootable in the intermediate stages. This means having to boot from Disk 0, then putting in Disk 1, then disk 2, before continuing the next phase of the installation. I tried to keep the installation as "Plain Vanilla" as possible.

OS/2 Devices OS/2 External Disk Support

I had to figure out what to include, and what to exclude, and this involved a lot of trial and error. For example, one of the choices was for "external diskette support". Since I had an "internal diskette drive", I didn't think I needed it. But after a full install, I discovered that it would not read or write floppy diskettes, so it appears that I do indeed need this support.

OS/2 supports two different file systems, FAT16 and the High Performance File System (HPFS). Since my partition was only 1.9GB in size, I chose just to use FAT16. HPFS supported larger disk partitions, longer file names, and faster performance, none of which I need for these purposes.

I thought it would be nice to get TCP/IP networking to work with my Ethernet card. However, after many attempts, I decided against this. I needed to focus on my mission, which was to decompress floppy diskettes. It was amusing to see that OS/2 supported all kinds of networking, including Token Ring, System Management, Remote Access, Mobile Access Services, File and Print.

IBM Means Three Things

Once all the options are chosen, OS/2 installation then proceeds to unpack and copy all the programs to the C: drive. During this process, IBM had informational splash screens. Here's one that caught my eye, titled "IBM Means Three Things" that listed three reasons to partner with IBM:

  1. Providing global solutions for a small planet
  2. Creating and Applying advanced technologies to improve with which customers run their businesses
  3. Constantly improving customer service with the products and services we provide

You might wonder how these OS/2 splash screens, written over 10 years ago, can appear almost identical to IBM's current [Smarter Planet] campaign. Actually, it is not that odd. IBM has been keeping to these same core principles since 1911, only the words to describe and promote these core values have changed.

OS/2 WARP screen

To access both OS/2 and DOS partitions, I installed Grand Unified Bootloader [Grub2] on the DOS partition under C:/BOOT/GRUB directory. However, when I boot OS/2, I cannot see the DOS partition. And when I boot DOS, I cannot see the OS/2 partition. Each operating system thinks its C: drive is the only partition on the system.

Now that I had OS/2 running, I was then able to install Stacker from two floppy diskettes. With this installed, I can compress and decompress data on either the hard disk, or on floppy diskettes. Most of the files were flat text documents and digital photos. After copying the data off the compressed disks onto my hard drive, I now can copy them off to a safe place.

To finish this project, I installed Ubuntu Linux on the remaining 76GB of disk space, which can access both the OS/2 and DOS drives FAT16 file systems natively. This allows me to copy files from OS/2 to DOS or vice versa.

OS/2 WARP Grub screen

Now that I know what data types are on the diskettes, I determined that I could have decompressed the data in just a few steps:

  • Set up a DOS partition on C: drive
  • Insert one of the compressed diskettes into the floppy drive
  • Copy the STACKER.EXE program from the floppy to the C: drive
  • Run "STACKER A:" to decompress the floppy diskette

However, now that I have a working DOS and OS/2 system, I can possibly review the rest of my floppy diskettes, some of which may require running programs natively on OS/2 or DOS. This brings me to an important lesson. If you are going to keep archive data for long-term retention, you need to choose file formats that can be read by current operating systems and programs. Installing older operating systems and programs to access proprietary formats can be quite time-consuming, and may not always be possible or desirable.

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