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This often increases the speed of image write operations by several times, at the cost of losing the simple sequential read/write semantics of normal memory. Additional bits which are provided on some computer architectures , such as AMD64 , allow the shadowing of ROM contents in memory (shadow ROM), and the configuration of memory-mapped I/O .
These mechanisms are intended to prevent only accidental data loss or attacks by computer viruses. A determined user can easily circumvent them either by covering a notch with adhesive tape or by creating one with a punch as appropriate, or sometimes by physically altering the media transport to ignore the write-protect mechanism.
The most common form, only available when using a full-size SD card, provides a physical write protection switch which allows the user to advise the host card reader to disallow write access. This does not protect the data on the card if the card reader hardware is not built to respect the write protection switch. [2]
Write protect: When set, the CPU cannot write to read-only pages when privilege level is 0 18: AM: Alignment mask: Alignment check enabled if AM set, AC flag (in EFLAGS register) set, and privilege level is 3 29: NW: Not-write through: Globally enables/disable write-through caching: 30: CD: Cache disable: Globally enables/disable the memory ...
An RW lock allows concurrent access for read-only operations, whereas write operations require exclusive access. This means that multiple threads can read the data in parallel but an exclusive lock is needed for writing or modifying data. When a writer is writing the data, all other writers and readers will be blocked until the writer is ...
In addition to its literal meaning, the term may be applied to a situation when the data written by one circuit can be read only by other circuitry. The most common occurrence of the latter situation is when a processor writes data to a write-only register of hardware the processor is controlling. The hardware can read the instruction but the ...
EEPROM or E 2 PROM (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.
Another form of one-time programmable memory device uses the same semiconductor chip as an ultraviolet-erasable programmable read-only memory (UV-EPROM), but the finished device is put into an opaque package, instead of the expensive ceramic package with transparent quartz window required for erasing. These devices are programmed with the same ...