System/36

The IBM System/36 was a simple and popular small business computer system, first shipped in 1983. It had a 17-year product lifespan.

The first model of the S/36 was the 5360. It weighed 800 pounds, cost (US) $100,000 and up, and ran at speeds up to 20 MHz, which in 1983 was faster than the "Personal Computers" on the market. The 5362 was a mere 150 pounds and cost (US) $20,000, and set the pace for corporate computing.

In the 1970s, the US Department of Justice brought an antitrust lawsuit against IBM, claiming it was using unlawful practices to knock out competitors. At this time, IBM had been about to consolidate its entire line (S/370, 4300, S/38, S/34) into one "family" of computers with the same ISAM database technology, programming languages, and hardware architecture. But after the lawsuit was filed, IBM decided it would have two families: the System/38 line, intended for large companies and representing IBM's future direction, and the System/36 line, intended for small companies who had used the company's legacy System/3/32/34 computers.

The System/36 used virtually the same RPG II, SDA, OCL, and other technologies that the System/34 used, though it was object-code incompatible. Its displays (at 24x80) were twice the size of its ancestor. The S/36 was a small business computer; it had an 8-inch diskette drive, between one and four hard drives in sizes of 30 to 716 MB, and memory from 256K up to 7MB. Tape drives were available as backup devices.

The S/36 used a command-line environment, but it was friendlier than the S/34 because of 100 or so "menus" that simplified the command process. Instead of typing "BLDLIBR MYLIB,100,30" to create a user program library, an operator could use menus to find the description "Create a user library" and fill in a simple form to accomplish the same goal.

RPG II was an improvement on RPG I, which had been based on card readers, disk packs, and printouts. RPG II allowed access to the "WORKSTN file" to allow a punchcard-based language to interact with a person sitting at a keyboard and monitor. A WORKSTN file was an output file (it wrote to the monitor) and also an input file (because it accepted the user's keyboard input).

Command keys became RPG indicators KA-KY, and different on-screen forms were recognized by different invisible control characters hidden in the forms themselves. Interestingly, since the user had to display a form on the screen in order to type, RPG II provided a way for a program to write output before accepting input. Many successful programmers moved from using the combined-primary WORKSTN file to using a combined-demand file, which had operation codes to read and write the display. There was even a way to code for multiple WORKSTNs; several people could sign on to the same copy of the same program in memory. The largest program size was 64k.

There were a few holdovers from the days of the System/32 (the "Bionic Desk" of 1975): the KEYBORD, CONSOLE, and DISPLAY files which provided unformatted access to the monitor and keyboard. Clever S/36 programmers could use a KEYBORD file to accept commands from the procedure (the "system input file") meaning that a program could be customized at run time without a recompilation.

 // LOAD MYPROG
 // FILE NAME-INPUT
 // RUN
 THIS IS CUSTOM DATA
 SO IS THIS
 /* (means end of data)

The System/36 was flexible and powerful:

• It allowed 36 monitors and printers to be connected together. All users could access the system's hard drive or any printer.
• It provided very good password security and resource security, allowing control over who was allowed to access any program or file.
• Devices could be as far as a mile from the system unit.
• Users could dial into a System/36 from anywhere in the world and get a 9600 baud connection, which was very fast in the 1980s and very quick for connections which used only screen text and no graphics.
• It allowed the creation of databases of very large size. It supported up to about 8 million records, and the largest 5360 with four hard drives in its extended cabinet could hold 1.453 gigabytes.
• The S/36 was "bulletproof," able to run run for six weeks or longer between restarts (IPLs).

In the late 1980s the US Department of Justice ended its case against IBM, and so IBM went forward with a system named the AS/400. The new system was a smaller and less-expensive S/38 with a more powerful database, and so was instantly popular among the 20,000 S/38 customers. But the company had trouble convincing the 300,000 S/34 and S/36 customers to migrate; people who paid $20k for their S/36 didn't want to pay $40k for the AS/400, especially because of the added expense of rewriting software and retraining personnel for it.

In 1994, IBM released the Advanced 36. Priced as low as $7995, it was the machine that allowed S/36 folks to get faster and more modern hardware while "staying 36." The Advanced 36 allowed SSP, the operating system of the S/36, to be contained within AS/400's OS/400 as a "virtual machine" so that it could be upgraded to a full-blown AS/400 for $15k.

The S/36 market was eventually devoured by AS/400's at the high end and PC's at the low end. Personal computers were not nearly the database equal of SSP, but time and technology had taken their toll on a system that had remained basically unchanged since 1983. By 2000, the Advanced 36 was withdrawn from marketing, and S/36s are disappearing rapidly from the marketplace.