|
Read-only Memory
Read-only memory (ROM) is a type of non-volatile memory used in computers and other electronic devices. Data stored in ROM cannot be electronically modified after the manufacture of the memory device. Read-only memory is useful for storing software that is rarely changed during the life of the system, also known as firmware. Software applications, such as video games, for programmable devices can be distributed as ROM cartridge, plug-in cartridges containing ROM. Strictly speaking, ''read-only memory'' refers to hard-wired memory, such as diode matrix or a #Solid-state ROM, mask ROM integrated circuit (IC), that cannot be electronically changed after manufacture. Although discrete circuits can be altered in principle, through the addition of Jump wire, bodge wires and the removal or replacement of components, ICs cannot. Correction of errors, or updates to the software, require new devices to be manufactured and to replace the installed device. Floating-gate ROM semiconductor ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
File-system Permissions
Typically, a file system maintains permission settings for each stored item commonly computer file, files and directory (computer), directories that either grant or deny the ability to manipulate file system items. Often the settings allow controlling access based on function such as read, change, navigate, and Execution (computing), execute and to different computer user, users and groups of users. One well-established technology was developed for Unix and later codified by POSIX. Another common technology is an access-control list (ACL) with multiple variants implemented in file systems and one codified by POSIX. Since POSIX defines both the older Unix-based technology as well as ACLs, the former is called ''traditional POSIX permissions'' for clarity even though it is not a well-known term. A permission-driven user interface tailors the functionality available to the user based on file system item permissions. For example, the interface might hide menu options that are not al ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Electrically Erasable Programmable Read-only Memory
EEPROM or E2PROM (electrically erasable programmable read-only memory) is a type of non-volatile memory. It is used in computers, usually integrated in microcontrollers such as smart cards and remote keyless systems, or as a separate chip device, to store relatively small amounts of data by allowing individual bytes to be erased and reprogrammed. EEPROMs are organized as arrays of floating-gate transistors. EEPROMs can be programmed and erased in-circuit, by applying special programming signals. Originally, EEPROMs were limited to single-byte operations, which made them slower, but modern EEPROMs allow multi-byte page operations. An EEPROM has a limited life for erasing and reprogramming, reaching a million operations in modern EEPROMs. In an EEPROM that is frequently reprogrammed, the life of the EEPROM is an important design consideration. Flash memory is a type of EEPROM designed for high speed and high density, at the expense of large erase blocks (typically 512 b ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Core Rope Memory
Core rope memory is a form of read-only memory (ROM) for computers. It was used in the UNIVAC I (Universal Automatic Computer I) and the UNIVAC II, developed by the Eckert-Mauchly Computer Corporation in the 1950s, as it was a popular technology for program and data storage in that era. It was later used in the 1960s by early NASA Mars space probes and then in the Apollo Guidance Computer (AGC), which was built by Raytheon. The software for the AGC was written by programmers at the Massachusetts Institute of Technology (MIT) Instrumentation Lab, and was woven into core rope memory by female workers in factories. Some programmers nicknamed the finished product ''LOL memory'', for ''Little Old Lady'' memory. Operation Similar to magnetic-core memory, magnetic rings (or cores) are used to determine the data of the software. Unlike magnetic-core memory, the cores themselves are not used to store the data; the way a core is wired controls whether that core represents a '0' or ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Apollo Guidance Computer
The Apollo Guidance Computer (AGC) was a digital computer produced for the Apollo program that was installed on board each Apollo command module (CM) and Apollo Lunar Module (LM). The AGC provided computation and electronic interfaces for guidance, navigation, and control of the spacecraft. The AGC was among the first computers based on silicon integrated circuits (ICs). The computer's performance was comparable to the first generation of home computers from the late 1970s, such as the Apple II, TRS-80, and Commodore PET. At around 2 cubic feet in size, AGC held 4,100 IC packages. The AGC has a 16-bit Word (computer architecture), word length, with 15 data bits and one [ arity bit. Most of the software on the AGC is stored in a special read-only memory known as core rope memory, fashioned by weaving wires through and around magnetic cores, though a small amount of read/write core memory is available. Astronauts communicated with the AGC using a numeric display and keyboard call ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Control Store
A control store is the part of a CPU's control unit that stores the CPU's microprogram. It is usually accessed by a microsequencer. A control store implementation whose contents are unalterable is known as a Read Only Memory (ROM) or Read Only Storage (ROS); one whose contents are alterable is known as a Writable Control Store (WCS). Implementation Early use Early control stores were implemented as a diode-array accessed via address decoders, a form of read-only memory. This tradition dates back to the ''program timing matrix'' on the MIT Whirlwind, first described in 1947. Modern VLSI processors instead use matrices of field-effect transistors to build the ROM and/or PLA structures used to control the processor as well as its internal sequencer in a microcoded implementation. IBM System/360 used a variety of techniques: CCROS (Card Capacitor Read-Only Storage) on the Model 30, TROS (Transformer Read-Only Storage) on the Model 40, and BCROS (Balanced Capacitor Read-Only ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
IBM System/370 Model 165
The IBM System/370 Model 165 (and the Model 155) were jointly announced June 30, 1970 as "designed for ... the Seventies." That same day IBM announced the 370/195. They were the first three models of the IBM System/370 line of computers. Since none of them came with virtual memory, "which was to be a hallmark of the 370 line", some said about these early members of the IBM System/370 family, especially about the 165 and 155, that they were not "the real 370 line." Three months later a fourth IBM System/370, the Model 145, was announced. Virtual memory The initially announced System/370 Models 165 and 155 systems did not support virtual memory. In 1972 an upgrade option was announced "to provide the hardware necessary to operate in a virtual memory mode." Unlike the IBM System/370 Model 145, which as early as June 1971 included the hardware necessary to support virtual memory, and for which a microcode update from a floppy disk, adding support for virtual memory, was announc ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
IBM System/370 Model 155
The IBM System/370 Model 155 (and the IBM System/370 Model 165, Model 165) were jointly announced Jun 30, 1970 as "designed for ... the Seventies." That same day IBM announced the 370/195. They were the first three models of the IBM System/370 line of computers. Since none of them came with virtual memory, "which was to be a hallmark of the 370 line", some said about these early members of the IBM System/370 family, especially about the 155 and 165, that they were not "the real 370 line." Three months later a fourth IBM System/370, the IBM System/370 Model 145, Model 145, was announced. Virtual memory The initially announced System/370 Models 155 and 165 systems did not support virtual memory. In 1972 an upgrade option was announced "to provide the hardware necessary to operate in a virtual memory mode." Unlike the IBM System/370 Model 145, which as early as June 1971 included the hardware necessary to support virtual memory, and for which a microcode update from a floppy dis ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
IBM System/370
The IBM System/370 (S/370) is a range of IBM mainframe computers announced as the successors to the IBM System/360, System/360 family on June 30, 1970. The series mostly maintains backward compatibility with the S/360, allowing an easy migration path for customers; this, plus improved performance, were the dominant themes of the product announcement. Early 370 systems differed from the 360 largely in their internal circuitry, moving from the Solid Logic Technology hybrid integrated circuits containing separate transistors to more modern monolithic integrated circuits containing multiple transistors per integrated circuit, which IBM referred to as Monolithic System Technology, or MST. The higher density packaging allowed several formerly optional features from the 360 line to be included as standard features of the machines, floating-point support for instance. The 370 also added a small number of new instructions. At the time of its introduction, the development of virtual mem ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
IBM System/360 Model 85
The IBM System/360 Model 85 is a high-end member of the System/360 family of computers, with many advanced features, and was announced in January 1968 and first shipped in December 1969. IBM built only about 30 360/85 systems because of "a recession in progress". Models The four models of the 360/85 are: I85 (512K), J85 (1M), K85 (2M) and L85 (4M), configured with two IBM 2365 Processor Storage units, four 2365 units, an IBM 2385 Processor Storage unit Model 1 (=2M), or an IBM 2385 Processor Storage unit Model 2 (=4M) respectively. The I85 includes two-way interleaved memory while the others provide four-way interleaving of memory access. Advanced/special features * The system console is L-shaped: one leg is the Main Control Panel, including a CRT, and the other leg includes 2 screens: "Microfiche Document Viewer" and "Indicator Viewer." * CPU cache, which IBM termed "high-speed buffer storage" - depending on the model and the situation, "the effective system storage cycle ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
IBM System/360
The IBM System/360 (S/360) is a family of mainframe computer systems announced by IBM 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 architecture and implementation, allowing IBM to release a suite of compatible designs at different prices. All but the only partially compatible Model 44 and the most expensive systems use microcode to implement the instruction set, featuring 8-bit byte addressing and fixed-point binary, fixed-point decimal and hexadecimal floating-point calculations. The System/360 family introduced IBM's Solid Logic Technology (SLT), which packed more transistors onto a circuit card, allowing more powerful but smaller computers. System/360's chief architect was Gene Amdahl, and the project was managed by Fred Brooks, responsible to Chairman Thomas J. Wat ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Transformer Read-only Storage
Transformer read-only storage (TROS) was a type of read-only memory (ROM) used between the mid-1940s to the late 1960s, prior to the common use of semiconductor ROM. TROS consisted of wires fed through and around transformer cores. The wires would register binary digits (1s and 0s) through inductance and separate wires sensing the change in current. Transformer read-only storages were first invented by T. L. Dimond in 1945 at Bell Laboratories for the No. 5 Crossbar switch to assist in the automatic message accounting (AMA) equipment. Later applications include the Bell Laboratories Model 6 computer and the IBM System/360 Model 20 and Model 40. TROS was considered simple in design, albeit with flaws that discouraged later applications due to demands for higher computer performance. Overview TROS was created by IBM as a read-only storage method for storing microcode for IBM computers. TROS used stacks of removable Mylar flexible printed wiring sheets that fitted onto fixed tr ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Flash Memory
Flash memory is an Integrated circuit, electronic Non-volatile memory, non-volatile computer memory storage medium that can be electrically erased and reprogrammed. The two main types of flash memory, NOR flash and NAND flash, are named for the NOR gate, NOR and NAND gate, NAND logic gates. Both use the same cell design, consisting of floating-gate MOSFETs. They differ at the circuit level, depending on whether the state of the bit line or word lines is pulled high or low; in NAND flash, the relationship between the bit line and the word lines resembles a NAND gate; in NOR flash, it resembles a NOR gate. Flash memory, a type of floating-gate memory, was invented by Fujio Masuoka at Toshiba in 1980 and is based on EEPROM technology. Toshiba began marketing flash memory in 1987. EPROMs had to be erased completely before they could be rewritten. NAND flash memory, however, may be erased, written, and read in blocks (or pages), which generally are much smaller than the entire devi ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
