System/360 or briefly S/360 designates a large computer architecture of the company IBM from the year 1964. The most important Design criteria were:

• General PUR-float. Before the S/360 were optimized computers either for commercial or for scientific-technical purposes.
• 8-bit character size. Contrary to contemporary architectures, which with 6-Bit units worked became bytes 8 bits used.
• 32 - or 64-Bit of floating decimal point words with hexadecimal basis.
• Sign at integer values is 1 bit
• Decimal numbers (packed storage) can have variable lengths from 1 to 31 places. In some "“high-level languages"” like for example RPG (programming language) only 15 places. Each number occupied thereby a half byte (coded 4 bits, binary decimal numbers), the sign occupies the last 4 bits in the last byte: "“C"” (1100) and "“F"” (1111) were the positive signs, "“D"” (1101) the minus sign. All other combinations were invalid signs. One must determine the position of the comma due to the operands when programming.
• Variable long character strings have a length field and not with a special character are locked.
• EBCDIC instead of ASCII code because of the simpler conversion from card code.
• Renouncement of a stack. This makes Linkage conventions necessary, since with subroutine references the status must become secured.
• In principle addressing indicated using a base register. Programs are so in principle independent of physical addresses.
• Binary addressing
• All registers are universal registers, which can be used both and accumulators and for the addressing (exception register 0). Advisable is to be used however as base register (addressing) only the registers starting from No. 3 (upto max. 8). Registers 1 and 2 are used by certain instructions (e.g. frame TRT) obligatorily. Registers 12 to 15 are used for the call of subroutines and some also still need one for other purposes. A register is enough to address straight around a storage area of 4096 bytes (4k byte). In the machine instructions stand for a storage address only 2 bytes for order, 4 bits for the register number and 12 bits for the DISPLACEMENT.
• The universal registers are 32 bits long, for addressing the right 24 bits are used, which makes an address area of 16 megabyte possible. With the instructions "“BAL"” and "“BALR"” (Branch and left) the return address is stored into a register, in the left 4 bits of the register the condition code is saved. Due to these characteristics it was not so simply possible with the follow-up systems to extend the address area beyond the 16 MT.

The S/360 - Architecture was developed in the course of the last forty years continuously further and culminates at present in architecture to that zSeries.

Operating systems

With the System/360 three operating systems, TOS/360 for installations without non removable disks, appeared DOS/360 for smaller and OS/360 for larger installations with disks. OS/360 is the forerunner of the current z/OS.

A characteristic represented the system 360/20. Originally pure punch card system was conceived (separation of tabulating machines) and had only a reduced instruction set as (machine instructions). The register width amounted to 16 bits with 8 instead of 16 registers.

Name meaning

The system had to be all comprehensive the requirement. Therefore one selected the number of 360 as reference to the maximum degree of an angle. The requirement could not be fulfilled however, so that afterwards the number was differently defined: 3 one rated as IBM standard and 60 for a product developed into the 1960ern. Therefore the successors S/370 and S/390 were called.

Related links

• Genes Amdahl et al.: Architecture OF the IBM System/360, 1964
• Heise: Before 40 years: the perfect computers

Articles in category "System/360"

We found here 6 articles.

Related Websites

We found here 4 related websites.

• Architecture of the IBM System/360
  1964 article coinciding with the announcement of the System/360 (S/360), the first family of computers...


• IBM 360/370/3090/390
  A condensed history of IBM mainframes and their operating systems from System/360 through System/390.


• System/360 - Wikipedia, the free encyclopedia
  System/360 Model 65 operator's console, with register value lamps and toggle ... IBM absolutely bet the company on the System/360 (US$5 billion in 1964 ...


• System/360 - Wikipedia, the free encyclopedia
  IBM's System/360 was the second most expensive. S/360 machines were also heavily ... IBM absolutely bet the company on the System/360 (US$5 billion in 1964 ...