System/360

Unlike most systems, IBM created an entire line of computers (or CPUs) from small to large, all running the same command set. This allowed customers to use a low-cost version of the family, and upgrade to larger systems if their needs grew. Some models (e.g., the 360/30) even offered the option of microcode emulation of the customer's previous computer (e.g., the IBM 1401, or the IBM 1620) so that old programs could still be run on the new machine.

This flexibility greatly lowered barriers to entry. With other machines customers had to choose between being able to afford a machine that might not have the power you needed, or instead purchasing one that guaranteed the power but cost so much as to be unattractive. The result was that many companies simply didn't buy computers. The S/360 changed the entire nature of the market, and companies could now buy "low end" machines without fear.

The S/360 family initially consisted of six computers and forty common peripherals; there were thirteen models in all. The cheapest model was the 360/20 with 24K of memory, only half the registers of other models and the instruction set was not binary-compatible with the rest of the range. The most significant model was the 360/67 (first shipped in August 1966), which was the first to offer virtual machine computing to its users through its CP-67 operating system, later called VM/370 (see: CMS/VM).

Operating System/360 (OS/360) was developed for the mid-range System/360 computers. The smaller machines used DOS/360 and the larger were supposed to use TSS/360 (Time-Sharing System, a Multics copy), but it never worked properly and was replaced with either CP-67, MTS (Michigan Time-Sharing System), TSO (Time-Sharing Option for OS/360) or one of several others.

The System/360 introduced a number of industry standards, such as 8-bit bytes (although there was financial pressure during development to reduce the byte to 4 or 6 bits) and byte addressable memory, 32-bit words, segmented and paged memory, the EBCDIC character set and was the first to use microcode.

The S/360 was replaced by the System/370 range in 1971. Gene Amdahl was the chief architect for the S/360.

The S/360 was the most expensive CPU project in history. The most expensive project of the 1960s was the Apollo moon rocket project; IBM's System/360 was the second most expensive. Fortune magazine at the time referred to it as IBM's "$5 Billion gamble" and they were right; IBM absolutely bet the company on this machine. ($5 billion in 1964 dollars translates to about $28 billion in 2002 dollars.) The bet paid off.

Being somewhat uncertain of the reliability and availability of the then new monolithic integrated circuits, IBM chose instead to design custom hybrid integrated circuits using discrete flip chip mounted glass encapsulated transistors and diodes with silk screened resistors on a ceramic substrate, then either encapsulated in plastic or covered with a metal lid. Several of these were then mounted on a small multi-layer printed circuit board to make a "SLT" ("Solid Logic Technology") module. Each "SLT" module had a socket on one edge that plugged into pins on the computer's backplane (the exact reverse of how most other company's modules were mounted).

See also List of IBM products.

External Link

• Solid Logic Technology (PDF)

This article (or an earlier version of it) contains material from FOLDOC, used with permission.

Referenced By