IBM System/360

The IBM System/360 (S/360) is a family of <a href="/facts/Mainframe_computer/nrBR6rWa">mainframe computer</a> systems announced by <a href="/facts/IBM/QszA7nwd">IBM</a> on April 7, 1964, and delivered between 1965 and 1978. System/360 was the first family of computers designed to cover both commercial and scientific applications and a complete range of applications from small to large. The design distinguished between <a href="/facts/Computer_architecture/tHtwxgR2">architecture</a> and implementation, allowing IBM to release a suite of compatible designs at different prices. All but the only partially compatible <a href="/facts/IBM_System%2f360_Model_44/EJ02nsd1">Model 44</a> and the most expensive systems use <a href="/facts/Microcode/CJQUvR7T">microcode</a> to implement the instruction set, featuring <a href="/facts/8-bit_computing/2CkhLNoH">8-bit</a> byte addressing and fixed-point binary, fixed-point decimal and <a href="/facts/IBM_hexadecimal_floating-point/EE3YS5aF">hexadecimal</a> <a href="/facts/Floating-point_arithmetic/eIckahxe">floating-point</a> calculations. The System/360 family introduced IBM's <a href="/facts/Solid_Logic_Technology/Uhd3R3PR">Solid Logic Technology</a> (SLT), which packed more transistors onto a circuit card, allowing more powerful but smaller computers.
System/360's chief architect was <a href="/facts/Gene_Amdahl/u83Qhvdw">Gene Amdahl</a>, the co-architect was <a href="/facts/Gerrit_Blaauw/5tK4hxVv">Gerrit Blaauw</a> and the project was managed by <a href="/facts/Fred_Brooks/1FNtgMgE">Fred Brooks</a>, responsible to Chairman <a href="/facts/Thomas_J._Watson_Jr./48bRYuD2">Thomas J. Watson Jr.</a> The commercial release was piloted by another of Watson's lieutenants, <a href="/facts/John_R._Opel/lHjTk6tG">John R. Opel</a>, who managed the launch of IBM's System/360 mainframe family in 1964. The slowest System/360 model announced in 1964, the <a href="/facts/IBM_System%2f360_Model_30/Jr2vfIjC">Model 30</a>, could perform up to 34,500 instructions per second, with memory from 8 to 64 <a href="/facts/Kibibyte/BNHUp9Qq">KB</a>. High-performance models came later. The 1967 <a href="/facts/IBM_System%2f360_Model_91/Yo9gocm4">IBM System/360 Model 91</a> could execute up to 16.6 <a href="/facts/Million_instructions_per_second/N23PAFGV">million instructions per second</a>. The larger 360 models could have up to 8 <a href="/facts/Mebibyte/BNHUp9Qq">MB</a> of <a href="/facts/Main_memory/wPHKFpdx">main memory</a>, though that much memory was unusual; a large installation might have as little as 256 KB of main storage, but 512 KB, 768 KB or 1024 KB was more common. Up to 8 megabytes of slower (8 microsecond) <a href="/facts/IBM_2361_Large_Capacity_Storage/Ir0YTR4d">Large Capacity Storage (LCS)</a> was also available for some models.
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. It influenced computer design for years to come; many consider it one of history's most successful computers. Application-level compatibility (with some restrictions) for System/360 software is maintained to the present day with the <a href="/facts/IBM_System_z/JJX9eAsD">System z</a> mainframe servers.

IBM System/360 open-in-new

IBM System/360