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The dirty bit for a page is set by the hardware whenever any word or byte in the page is written into, indicating that the page has been modified. When a page is selected for replacement, the modify bit is examined. If the bit is set, the page has been modified since it was read in from the disk. In this case, the page must be written to the disk.
For each byte of the input stream Perform 16-bit bitwise right rotation by 1 bit on the checksum; Add the byte to the checksum, and apply modulo 2 ^ 16 to the result, thereby keeping it within 16 bits; The result is a 16-bit checksum; The above algorithm appeared in Seventh Edition Unix. The System V sum, -s in GNU sum and -o2 in FreeBSD cksum:
For example, when shifting a 32 bit unsigned integer, a shift amount of 32 or higher would be undefined. Example: If the variable ch contains the bit pattern 11100101, then ch >> 1 will produce the result 01110010, and ch >> 2 will produce 00111001. Here blank spaces are generated simultaneously on the left when the bits are shifted to the right.
A message that is m bits long can be viewed as a corner of the m-dimensional hypercube. The effect of a checksum algorithm that yields an n-bit checksum is to map each m-bit message to a corner of a larger hypercube, with dimension m + n. The 2 m + n corners of this hypercube represent all possible received messages.
In computer programming, a bitwise operation operates on a bit string, a bit array or a binary numeral (considered as a bit string) at the level of its individual bits.It is a fast and simple action, basic to the higher-level arithmetic operations and directly supported by the processor.
A global replacement algorithm is free to select any page in memory. Local page replacement assumes some form of memory partitioning that determines how many pages are to be assigned to a given process or a group of processes. Most popular forms of partitioning are fixed partitioning and balanced set algorithms based on the working set model ...
An Adler-32 checksum is obtained by calculating two 16-bit checksums A and B and concatenating their bits into a 32-bit integer. A is the sum of all bytes in the stream plus one, and B is the sum of the individual values of A from each step. At the beginning of an Adler-32 run, A is initialized to 1, B to 0. The sums are done modulo 65521 (the ...
On the other hand, a hard disk whose capacity is specified by the manufacturer as "10 gigabytes" or "10 GB", holds 10 × 10 9 = 10 000 000 000 bytes, or a little more than that, but less than 10 × 2 30 = 10 737 418 240 and a file whose size is listed as "2.3 GB" may have a size closer to 2.3 × 2 30 ≈ 2 470 000 000 or to 2.3 × 10 9 = 2 300 ...