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Incomputer architecture,31-bitintegers,memory addresses, or otherdata units are those that are 31bits wide.
In 1983,IBM introduced 31-bit addressing in theSystem/370-XAmainframe architecture as an upgrade to the24-bit physical and virtual,[1] and transitional 24-bit-virtual/26-bit physical,[2][3] addressing inSystem/370.[4][5] This enhancement allowed address spaces to be 128 times larger, permitting programs to address memory above 16 MB (referred to as "above the line").[6][1] Support forCOBOL,FORTRAN and later onLinux/390 was included.
In the early 1980s, theMotorola 68012 was introduced; it had32-bit data and address registers, as did theMotorola 68010, but instead of providing the lower 24 bits of an address, it did so for all but bit 30 on the address pins.[7]
TheLibrascope LGP-30 was an early off-the-shelf computer. The LGP-30 was first manufactured in 1956,[8] at a retail price of $47,000,[citation needed] equivalent to $540,000 in 2024.[9]
It was abinary, 31-bit word computer with a 4096-worddrum memory. There were 32 bit locations per drum word, but only 31 were used, permitting a "restoration of magnetic flux in the head" at the 32nd bit time. The number ofvacuum tubes was minimized by using solid-statediode logic, abit-serial architecture and multiple use of each of its 15 flip-flops.
The LGP-30 was commonly referred to as a desk computer. Its height, width, and depth, excluding the typewriter shelf, was 33 by 44 by 26 inches (84 by 112 by 66 cm). It weighed about 800 pounds (360 kg), and was mounted on sturdy casters which facilitated moving the unit.
In theSystem/360, other than the360/67, and earlySystem/370 architectures, thegeneral-purpose registers were 32 bits wide, the machine did 32-bit arithmetic operations, and addresses were always stored in 32-bit words, so the architecture was considered32-bit, but the machines ignored the top 8 bits of the address resulting in24-bit addressing.
With theSystem/370-XA architecture and theIBM Enterprise Systems Architecture, in addition to a 24-bit addressing mode for compatibility with older applications, there is a 31-bit addressing mode, in which only the high order bit (bit 0) in the word is ignored for addressing. An exception is that mode-switching instructions also use bit 0. There were at least two reasons that IBM did not implement the 32-bit addressing of the 360/67
The 64-bitz/Architecture also supports 24-bit and 31-bit addressing modes for compatibility with older applications.
Interpreters for Ruby and Smalltalk languages use the lowest bit to tell whether a value is an unboxed integer or not. This means that on 32-bit machines (or16-bit machines with 32-bit pointers), 31-bit integers are unboxed. In case of overflow, the result is fit into a boxed object, which means that it has to be allocated and garbage-collected. Thus if you have 32-bit values that don't fit in the 31-bit signed format, they will be very inefficient in those interpreters. Same goes with 63-bit unboxed integers on 64-bit computers. Similar designs may be found in LISP and some of the other languages whose variables can take values of any type. In some cases, there was hardware support for this kind of design: seeTagged architecture andLisp machine.
{{cite book}}:|work= ignored (help)Librazette: July, 1956 –Royal Precision Plans – LGP-30 Promotion; November, 1956 –LGP-30, Flow Computer Spearhead – Commercial Sales and Production – They're In Production andPaul Coates Will Feature LGP-30 on Dec. TVshows[verification needed]