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Base Addresses
In computing, a base address is an address serving as a reference point ("base") for other addresses. Related addresses can be accessed using an ''addressing scheme''. Under the ''relative addressing'' scheme, to obtain an absolute address, the relevant base address is taken and an offset (aka displacement) is added to it. Under this type of scheme, the base address is the lowest numbered address within a prescribed range, to facilitate adding related positive-valued offsets. In IBM System/360 architecture, the base address is a 24-bit value in a general register (extended in steps to 64 bits in z/Architecture), and the offset is a 12 bit value in the instruction (extended to 20 bits in z/Architecture). See also * Index register An index register in a computer's central processing unit, CPU is a processor register (or an assigned memory location) used for pointing to operand addresses during the run of a program. It is useful for stepping through String (computer science . ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Computing
Computing is any goal-oriented activity requiring, benefiting from, or creating computer, computing machinery. It includes the study and experimentation of algorithmic processes, and the development of both computer hardware, hardware and software. Computing has scientific, engineering, mathematical, technological, and social aspects. Major computing disciplines include computer engineering, computer science, cybersecurity, data science, information systems, information technology, and software engineering. The term ''computing'' is also synonymous with counting and calculation, calculating. In earlier times, it was used in reference to the action performed by Mechanical computer, mechanical computing machines, and before that, to Computer (occupation), human computers. History The history of computing is longer than the history of computing hardware and includes the history of methods intended for pen and paper (or for chalk and slate) with or without the aid of tables. ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Memory Address
In computing, a memory address is a reference to a specific memory location in memory used by both software and hardware. These addresses are fixed-length sequences of digits, typically displayed and handled as unsigned integers. This numerical representation is based on the features of CPU (such as the instruction pointer and incremental address registers). Programming language constructs often treat the memory like an array. Types Physical addresses A digital computer's main memory consists of many memory locations, each identified by a unique physical address (a specific code). The CPU or other devices can use these codes to access the corresponding memory locations. Generally, only system software (such as the BIOS, operating systems, and specialized utility programs like memory testers) directly addresses physical memory using machine code instructions or processor registers. These instructions tell the CPU to interact with a hardware component called the memory c ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Offset (computer Science)
In computer science, an offset within an array or other data structure object is an integer indicating the distance (displacement) between the beginning of the object and a given element or point, presumably within the same object. The concept of a distance is valid only if all elements of the object are of the same size (typically given in bytes or words). For example, if A is an array of characters containing "abcdef", the fourth element containing the character 'd' has an offset of three from the start of A. In assembly language In computer engineering and low-level programming (such as assembly language), an offset usually denotes the number of address locations added to a base address in order to get to a specific absolute address. In this (original) meaning of offset, only the basic address unit, usually the 8-bit byte, is used to specify the offset's size. In this context an offset is sometimes called a relative address. In IBM System/360 instructions, a 12-bit of ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
IBM System/360 Architecture
The IBM System/360 architecture is the model independent architecture for the entire S/360 line of mainframe computers, including but not limited to the instruction set architecture. The elements of the architecture are documented in the ''IBM System/360 Principles of Operation'' and the ''IBM System/360 I/O Interface Channel to Control Unit Original Equipment Manufacturers' Information'' manuals. Features The System/360 architecture provides the following features: * 16 32-bit general-purpose registers * 4 64-bit floating-point registers * 64-bit processor status register (PSW), which includes a 24-bit instruction address * 24-bit (16 MB) byte-addressable memory space * Big-endian byte/word order * A ''standard instruction set'', including fixed-point binary arithmetic and logical instructions, present on all System/360 models (except the Model 20, see below). ** A ''commercial instruction set'', adding decimal arithmetic instructions, is optional on some models, as ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Z/Architecture
z/Architecture, initially and briefly called ESA Modal Extensions (ESAME), is IBM's 64-bit complex instruction set computer (CISC) instruction set architecture, implemented by its mainframe computers. IBM introduced its first z/Architecture-based system, the z900, in late 2000. Subsequent z/Architecture systems include the IBM z800, z990, z890, System z9, System z10, zEnterprise 196, zEnterprise 114, zEC12, zBC12, z13, z14, z15, z16, and z17. z/Architecture retains backward compatibility with previous 32-bit-data/31-bit-addressing architecture ESA/390 and its predecessors back to the 32-bit-data/24-bit-addressing System/360. The IBM z13 is the last z Systems server to support running an operating system in ESA/390 architecture mode. However, all 24-bit and 31-bit problem-state application programs originally written to run on the ESA/390 architecture will be unaffected by this change. Features z/Architecture includes almost all of the features of ESA/390, and a ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Index Register
An index register in a computer's central processing unit, CPU is a processor register (or an assigned memory location) used for pointing to operand addresses during the run of a program. It is useful for stepping through String (computer science), strings and Array data structure, arrays. It can also be used for holding loop iterations and counters. In some Instruction set architecture, architectures it is used for read/writing blocks of memory. Depending on the architecture it may be a dedicated index register or a general-purpose register. Some instruction sets allow more than one index register to be used; in that case additional instruction fields may specify which index registers to use. Generally, the contents of an index register is added to (in some cases subtracted from) an ''immediate'' address (that can be part of the instruction itself or held in another register) to form the "effective" address of the actual data (operand). Special instructions are typically provided ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Rebasing
In computing, rebasing is the process of modifying data based on one reference to another. It can be one of the following: Shared libraries Rebasing is the process of creating a shared library image in such a way that it is guaranteed to use virtual memory without conflicting with any other shared libraries loadable in the system. IBM VM/370 ''discontinuous saved segments'' (DCSS) were an early example of this technique, though not called ''rebasing''. The technique is used extensively on Win32 platforms to avoid the overhead of address relocation of system DLLs by the loader. Some security extensions to Linux/x86 use rebasing to force the use of code addresses below 0x00ffffff in order to introduce a 0x00 byte into all code pointers; This eliminates a certain class of buffer overflow security problems related to improper checking of null-terminated strings, common in the C programming language. Other uses * Rebasing is the act of moving changesets to a different bra ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
