chapter 3 Flashcards
the process of changing the address of an instruction or data item to the address in main memory at which it is to be loaded or relocated.
address resolution
the name given to several registers, allocated to each active process, whose contents associate several of the process segments and page numbers with their main memory addresses.
associative memory
a small, fast memory used to hold selected data and to provide faster access than would otherwise be possible.
cache memory
the elapsed time between two ticks of the computer’s system clock.
clock cycle
a variation of the LRU policy that removes from the main
the memory of the pages that show the least amount of activity during recent clock cycles.
clock page replacement policy
a memory allocation scheme that loads a program’s page into mem- ory at the time it is needed for processing.
demand paging
in a paged or segmented memory allocation environment, the difference between a page’s relative address and the actual machine language address. Also called offset.
displacement
an unusual circumstance through which adding more page frames causes an increase in page interrupts when using a FIFO page replacement policy.
FIFO anomaly
a page replacement policy that removes from main memory the pages that were brought in first.
first-in first-out (FIFO) policy
a table in main memory that contains two values for each active job— the size of the job and the memory location where its page map table is stored.
Job Table (JT)
a page-replacement policy that removes from main memory the pages that show the least amount of recent activity.
least recently used (LRU) policy
behavior observed in many executing programs in which memory locations recently referenced, and those near them, are likely to be referenced in the near future.
locality of reference
a table in main memory that contains as many entries as there are page frames and lists the location and free/busy status for each one.
Memory Map Table (MMT)
offset
see displacement.
a fixed-size section of a user’s job that corresponds in size to page frames in main
memory.
page
a type of hardware interrupt caused by a reference to a page not residing in memory. The effect is to move a page out of main memory and into secondary storage so another page can be moved into memory.
page fault
the part of the Memory Manager that determines if there are empty page frames in memory so that the requested page can be immediately copied from secondary storage, or determines which page must be swapped out if all page frames are busy. Also known as a page interrupt handler.
page fault handler
an individual section of main memory of uniform size into which a single page may be loaded without causing external fragmentation.
page frame
a table in main memory with the vital information for each page including the page number and its corresponding page frame memory address.
Page Map Table (PMT)
an algorithm used by virtual memory systems to decide which page or segment to remove from main memory when a page frame is needed and memory is full.
page replacement policy
the process of moving a page out of main memory and into secondary storage so another page can be moved into memory in its place.
page swapping
a memory allocation scheme based on the concept of divid- ing a user’s job into sections of equal size to allow for noncontiguous program storage during execution.
paged memory allocation
code that can be used by two or more processes at the same time; each shares the same copy of the executable code but has separate data areas.
reentrant code
a division in a disk’s track, sometimes called a “block.” The tracks are divided into sectors during the formatting process.
sector
a variable-size section of a user’s job that contains a logical grouping of code.
segment
a table in main memory with the vital information for
each segment including the segment number and its corresponding memory address.
Segment Map Table (SMT)
a memory allocation scheme based on the concept of dividing a user’s job into logical groupings of code and loading them into memory as needed to minimize fragmentation.
segmented/demand paged memory allocation
a memory allocation scheme based on the concept of dividing a user’s job into logical groupings of code to allow for noncontiguous pro- gram storage during execution.
segmented memory allocation
also called a “subprogram,” a segment of a program that can perform a specific function. Subroutines can reduce programming time when a specific function is required at more than one point in a program.
subroutine
a phenomenon in a virtual memory system where an excessive amount of page swapping back and forth between main memory and secondary storage results in higher overhead and little useful work.
thrashing
a technique that allows programs to be executed even though they are not stored entirely in memory.
virtual memory
a collection of pages to be kept in main memory for each active process in a virtual memory environment.
working set
