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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.
WORM drives preceded the invention of the CD-R, DVD-R and BD-R.An example was the IBM 3363. [1] These drives typically used either a 5.1 in (13 cm) or a 12 in (30 cm) disc in a cartridge, with an ablative optical layer that could be written to only once, and were often used in places like libraries that needed to store large amounts of data.
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 .
A reference to a memory location includes a value that identifies a segment and an offset within that segment. A segment descriptor may limit access rights, e.g., read only, only from certain rings. The x86 architecture has multiple segmentation features, which are helpful for using protected memory on this architecture. [1]
Segments can be defined to be either code, data, or system segments. Additional permission bits are present to make segments read only, read/write, execute, etc. In protected mode, code may always modify all segment registers except CS (the code segment selector). This is because the current privilege level (CPL) of the processor is stored in ...
A Replay Protected Memory Block (RPMB) is provided as a means for a system to store data to the specific memory area in an authenticated and replay protected manner and can only be read and written via successfully authenticated read and write accesses. The data may be overwritten by the host but can never be erased.
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 ...
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 ...