| Processors | |||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|
| 4-bit | 8-bit | 12-bit | 16-bit | 18-bit | 24-bit | 31-bit | 32-bit | 36-bit | 48-bit | 64-bit | 128-bit |
| Applications | |||||||||||
| 8-bit | 16-bit | 31-bit | 32-bit | 64-bit | |||||||
| Data Sizes | |||||||||||
| 4-bit | 8-bit | 16-bit | 32-bit | 64-bit | 128-bit | ||||||
| nibble byte octet word dword qword | |||||||||||
In computer architecture, 31-bit integers, memory addresses, or other data units are those that are at most 31 bits (32 bits minus 1 unused/reserved bit) wide. The Intel 4004, the world's first commercially available single- chip Microprocessor, was a 4-bit CPU. Eight-bit CPUs normally use an 8-bit data bus and a 16-bit address bus which means that their Address space is limited to 64 KBs This is not a "natural Possibly the most well-known 18-bit computer architectures are the PDP-1, PDP-4, PDP-7, PDP-9 and PDP-15 Minicomputers produced The IBM System/360, announced in 1964, was an extremely popular computer system with 24-bit addressing and 32-bit general registers and arithmetic The range of Integer values that can be stored in 32 bits is 0 through 4294967295 or −2147483648 through 2147483647 using Two's complement encoding Many early computers aimed at the scientific market had a 36- Bit word length. Computers with 48-bit words include CDC 1604 and BESM-6. The IBM AS/400, in its CISC variants is a 48-bit addressing system '64-bit' CPUs have existed in Supercomputers since the 1960s and in RISC -based workstations and servers since the early 1990s. A 32-bit application is Software that runs in a 32-bit flat Address space (a Flat memory model) '64-bit' CPUs have existed in Supercomputers since the 1960s and in RISC -based workstations and servers since the early 1990s. A nibble (often nybble) is the Computing term for a four- Bit aggregation or half an octet (an octet being an 8-bit Byte A byte (pronounced "bite" baɪt is the basic unit of measurement of information storage in Computer science. A nibble (often nybble) is the Computing term for a four- Bit aggregation or half an octet (an octet being an 8-bit Byte A byte (pronounced "bite" baɪt is the basic unit of measurement of information storage in Computer science. In Computing, an octet is a grouping of eight Bits Octet, with the only exception noted below always refers to an entity having exactly eight In Computing, " word " is a term for the natural unit of data used by a particular computer design In Computing, " word " is a term for the natural unit of data used by a particular computer design In Computing, " word " is a term for the natural unit of data used by a particular computer design In Computer engineering, computer architecture is the conceptual design and fundamental operational structure of a Computer system In computer science the term integer is used to refer to a Data type which represents some finite subset of the mathematical Integers These are also known as In Computer science, a memory address is an identifier for a memory location at which a Computer program or a hardware device can store a piece of data Debt AIDS Trade in Africa (or DATA) is a Multinational non-government organization founded in January 2002 in London by U2 's A bit is a binary digit, taking a value of either 0 or 1 Binary digits are a basic unit of Information storage and communication Also, 31-bit CPU and ALU architectures are those that are based on registers, address buses, or data buses of that size. In Computing, an arithmetic logic unit ( ALU) is a Digital circuit that performs Arithmetic and Logical operations In Computer engineering, computer architecture is the conceptual design and fundamental operational structure of a Computer system In Computer architecture, a processor register is a small amount of storage available on the CPU whose contents can be accessed more quickly than storage An address bus is a Computer bus, controlled by CPUs or DMA -capable Peripherals for specifying the Physical addresses of computer In Computer architecture, a bus is a subsystem that transfers data between computer components inside a Computer or between computers
Perhaps the only computing architecture based on 31-bit addressing is one of computing's most famous and most profitable. In 1983, IBM introduced 31-bit addressing in the System/370-XA mainframe architecture as an upgrade to the 24-bit addressing of earlier models. International Business Machines Corporation abbreviated IBM and nicknamed "Big Blue", is a multinational Computer Technology The IBM System/370 (often S/370) was a model range of IBM mainframes announced on June 30, 1970 Mainframes (often colloquially referred to as Big Iron) are Computers used mainly by large organizations for critical applications typically bulk data This enhancement allowed address spaces to be 128 times larger, permitting programs to address memory above 16 MiB (referred to as "above the line"). A mebibyte (a contraction of me ga bi nary byte) is a unit of Information or Computer storage, abbreviated MiB.
In the System/360 and early System/370 architectures, addresses were always stored in 32-bit words, but the machines ignored the top 8 bits of the address resulting in 24-bit addressing. The IBM System/360 ( S/360) is a Mainframe computer system family announced by IBM on April 7, 1964. The IBM System/370 (often S/370) was a model range of IBM mainframes announced on June 30, 1970 With the XA extension, no bits in the word were ignored.
The transition was tricky: assembly language programmers had been using the spare byte at the top of addresses for flags for almost twenty years. IBM chose to support two forms of addressing to minimize the pain: if the most significant bit (bit 0) of a 32-bit address was on, the next 31 bits were interpreted as the virtual address. In Computing, the most significant bit ( msb) is the Bit position in a binary number having the greatest value If the most significant bit was off, then only the lower 24 bits were treated as the address (just as with pre-XA systems). Thus programs could continue using the seven low-order bits of the top byte for other purposes as long as they left the top bit off. The only programs requiring modification were those that set the top (leftmost) bit of a word containing an address. This also affected address comparisons: The leftmost bit of a word is also interpreted as a sign-bit, indicating a negative number if bit 0 is on. Programs that use signed arithmetic comparison instructions could get reversed results. Two equivalent addresses could be compared as non-equal if one of them had the sign bit turned on even if the remaining bits were identical. Fortunately, most of this was invisible to programmers using high-level languages like COBOL or FORTRAN, and IBM aided the transition with dual mode hardware for a period of time. COBOL (ˈkoʊbɒl is one of the oldest programming languages still in active use Fortran (previously FORTRAN) is a general-purpose, procedural, imperative Programming language that is especially suited to
Certain machine instructions in this 31-bit architecture alter the addressing mode bit as a possibly intentional side effect. For example, the original subroutine call instruction BAL stores certain status information in the top byte of the return address. A BAS instruction was added to support 31-bit return addresses.
In the 1990s IBM introduced 370/ESA architecture (later named 390/ESA and finally ESA/390 or System/390, in short S/390), completing the evolution to full 31-bit virtual addressing and keeping this addressing mode flag. ESA/390 (Enterprise Systems Architecture/390 was introduced in September 1990 and is IBM 's last 31-bit -address/ 32-bit -data mainframe computing These later architectures support more than 2 GiB of physical memory and support multiple concurrent address spaces up to 2 GiB each in size. A gibibyte (a contraction of gi ga bi nary byte) is a unit of Information or Computer storage, abbreviated GiB. As of mid-2006 there still are not too many programs unduly constrained by this multiple 31-bit architecture.
Nonetheless, IBM broke the 2 GiB linear addressing barrier ("the bar") in 2000 with the introduction of the first 64-bit z/Architecture system, the IBM zSeries Model 900. '64-bit' CPUs have existed in Supercomputers since the 1960s and in RISC -based workstations and servers since the early 1990s. z/Architecture, initially called ESA Modal Extensions ( ESAME) refers to IBM 's 64-bit computing architecture for a current generation IBM System z, or earlier IBM eServer zSeries, is a brand name designated by IBM to all its Mainframe computers In 2000 IBM rebranded the existing Unlike the XA transition, z/Architecture does not reserve a top bit to identify earlier code. Yet z/Architecture does maintain compatibility with 24-bit and 31-bit code, even older code running concurrently with newer 64-bit code.
Since Linux/390 was first released for the existing 32-bit data/31-bit addressing hardware in 1999, initial mainframe Linux applications compiled in pre-z/Architecture mode are also limited to 31-bit addressing. Linux on System z is the collective term for the Linux operating system compiled to run on IBM mainframes especially System z machines This limitation disappeared with 64-bit hardware, 64-bit Linux on zSeries, and 64-bit Linux applications. The 64-bit Linux distributions still support 31-bit programs.
IBM's 31-bit architecture supports expanded storage, allowing 31-bit code to make use of additional memory. However, at any one instant, a maximum of 2 GiB is in each working address space. For 31-bit Linux it is possible to assign memory above the 2 GiB bar as a RAM disk.
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