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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.
An access matrix can be envisioned as a rectangular array of cells, with one row per subject and one column per object. The entry in a cell – that is, the entry for a particular subject-object pair – indicates the access mode that the subject is permitted to exercise on the object. Each column is equivalent to an access control list for the ...
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]
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 ...
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 ...
A forensic disk controller or hardware write-block device is a specialized type of computer hard disk controller made for the purpose of gaining read-only access to computer hard drives without the risk of damaging the drive's contents.
It is one type of read-only memory (ROM). PROMs are used in digital electronic devices to store permanent data, usually low level programs such as firmware or microcode . The key difference from a standard ROM is that the data is written into a ROM during manufacture, while with a PROM the data is programmed into them after manufacture.