The System/360 family introduced IBM's Solid Logic Technology (SLT), which packed more transistors onto a circuit card, allowing more powerful but smaller computers.

[3] System/360's chief architect was Gene Amdahl, and the project was managed by Fred Brooks, responsible to Chairman Thomas J. Watson Jr.[4] The commercial release was piloted by another of Watson's lieutenants, John R. Opel, who managed the launch of IBM's System 360 mainframe family in 1964.

The IBM 360 was extremely successful, allowing customers to purchase a smaller system knowing they could expand it, if their needs grew, without reprogramming application software or replacing peripheral devices.

Customers were frustrated that major investments, often entirely new machines and programs, were required when seemingly small performance improvements were needed.

In meetings at the New Englander Motor Hotel in Greenwich, Connecticut, SPREAD developed a new concept for the next generation of IBM machines.

At the time, new technologies were coming into the market including the introduction of replacement of individual transistors with small-scale integrated circuits and the move to an 8-bit byte from the former 6-bit oriented words.

A single instruction set architecture (ISA) included instructions for binary, floating-point, and decimal arithmetic, string processing, conversion between character sets (a major issue before the widespread use of ASCII) and extensive support for file handling, among many other features.

[8] A new team was organized under the direction of Bob Evans, who personally persuaded CEO Thomas J. Watson Jr. to develop the new system.

Gene Amdahl was the chief architect of the computers themselves, while Fred Brooks was the project lead for the software and Erich Bloch led the development of IBM's hybrid integrated circuit designs, Solid Logic Technology.

Specifically, depending on the machine, some instructions might not be directly supported in hardware, and would instead be completed using small programs, in an internal machine-specific code, stored in read only memory, or what today is known as microcode.

[10] So a model intended for use with accounting might choose to implement the decimal math directly in hardware, and leave the floating-point instructions to be handled by the subprograms.

Using previous designs, the system that performed floating point would generally not have any support for decimal math at all, and would require the customer to write such a package or buy another machine.

This meant that a single lineup could have machines tailored to match the price and performance niches that formerly demanded entirely separate computer systems.

New features could be added without violating architectural definitions: the 65 had a dual-processor version (M65MP) with extensions for inter-CPU signalling; the 85 introduced cache memory.

The Model 67, announced in August 1965, was the first production IBM system to offer dynamic address translation (virtual memory) hardware to support time-sharing.

[18] The IBM 5100 portable computer, introduced in 1975, offered an option to execute the System/360's APL.SV programming language through a hardware emulator.

Special radiation-hardened and otherwise somewhat modified System/360s, in the form of the System/4 Pi avionics computer, are used in several fighter and bomber jet aircraft.

The U.S. Federal Aviation Administration operated the IBM 9020, a special cluster of modified System/360s for air traffic control, from 1970 until the 1990s.

If the Commercial Instruction Set option was installed, packed decimal arithmetic could be performed as memory-to-memory with some memory-to-register operations.

A channel is a specialized processor with the instruction set optimized for transferring data between a peripheral and main memory.

Also, the byte-multiplexer channels on larger models have an optional selector subchannel section that would accommodate tape drives.

On higher speed models, multiple selector channels, which could operate simultaneously or in parallel, improved overall performance.

The substrate was then covered with a metal lid or encapsulated in plastic to create a "Solid Logic Technology" (SLT) module.

Up to twenty SLT boards could be assembled side-by-side (vertically and horizontally, max 4 high by 5 wide) to form a "logic gate".

The second digit described the type of component, as follows: IBM developed a new family of peripheral equipment for System/360, carrying over a few from its older 1400 series.

Interfaces were standardized, allowing greater flexibility to mix and match processors, controllers and peripherals than in the earlier product lines.

A typical use was overlay linkage (e.g. for OS and application subroutines) for program sections written to alternate in the same memory regions.

The 2305, although often called a "drum" was actually a head-per-track disk device, with 12 recording surfaces and a data transfer rate up to 3 MB/s.

The IBM Data Cell was proposed to fill cost/capacity/speed gap between magnetic tapes—which had high capacity with relatively low cost per stored byte—and disks, which had higher expense per byte.

[56] Despite having been sold or leased in very large numbers for a mainframe system of its era, only a few of System/360 computers remain—mainly as non-operating property of museums or collectors.