D686 - Operating Systems - Chapter 8

cache

a temporary storage area that holds copies of frequently accessed data to speed up processing

bind

to connect or link together, such as associating a symbolic address with a relocatable address for program execution

absolute code

program instructions that reference fixed memory addresses for direct execution

logical address

address generated by the CPU that requires translation to a physical address for use in memory, essentially the same as a virtual address in this context

physical address

actual location in physical memory where data or instructions are stored

logical space address

range of all addresses generated by a program before translation into physical addresses

physical address space

range of all physical addresses available in a computer system

memory management unit (MMU)

hardware enabling a CPU to access and translate addresses between logical and physical memory

dynamic loading

loading of program routines into memory only when called during execution, not at program start

dynamically linked libraries (DLLs)

system libraries linked to user programs at runtime, allowing shared resources across processes

static linking

combining system libraries into a binary program image before execution, as done by the loader

shared libraries

libraries loaded once into memory and accessed by multiple processes, facilitating efficient memory use

contiguous memory allocation

A memory allocation method in which each process is contained in a single section of memory that is contiguous to the section containing the next process.

variable-partition 

A simple memory-allocation scheme in which each partition of memory contains exactly one process.

hole

In variable partition memory allocation, a contiguous section of unused memory. Also an alternative rock band formed by Courtney Love.

dynamic storage-allocation problem

The problem of how to satisfy a request for size n of memory from a list of free holes.

first-fit

In memory allocation, selecting the first hole large enough to satisfy a memory request.

best-fit

In memory allocation, selecting the smallest hole large enough to satisfy the memory request.

worst-fit

In memory allocation, selecting the largest hole available.

external fragmentation

Fragmentation in which available memory contains holes that together have enough free space to satisfy a request but no single hole is large enough to satisfy the request. More generally, the fragmentation of an address space into small, less usable chunks.

50-percent rule

A statistical finding that fragmentation may result in the loss of 50 percent of space.

dynamic storage allocation

the process of assigning and freeing memory during a program's run time as needed

memory protection

a method to control and restrict how programs access memory in a computer, preventing errors and security issues

partitioning 

dividing memory into sections to manage different processes

fixed partitioning memory management

a scheme dividing memory into fixed-sized partitions, each holding a single process

overlays

a method of loading only necessary parts of a program into memory, swapping others as needed

variable partition memory management scheme

a method where memory is allocated dynamically, varying in size based on process needs

fragmented

memory scattered into non-contiguous pieces, making the efficient use of memory challenging

external fragmentation

unused memory scattered in non-contiguous blocks, causing inefficient use of memory

compaction

the process of consolidating fragmented free memory space to create a large contiguous block

internal fragmentation

wasted memory within allocated regions due to fixed-size partitions

What defines a logical address space using base and limit registers?

Base and limit registers

How do base and limit registers contribute to hardware address protection?

By defining the range of accessible addresses

Which process binds logical addresses to physical addresses?

Address binding

Which characteristic differentiates a logical address space from a physical address space?

Logical address space is used by the CPU, while physical address space is used by memory.

Which mechanism protects memory from being accessed incorrectly?

Memory protection

How is memory allocated and managed in a system?

By using fixed and variable partitions

What ensures that each process has its own separate memory space?

Memory protection

Which issue is caused by fixed partition memory management?

Internal fragmentation

What causes external fragmentation in memory management?

Dynamic allocation of memory blocks

What is the 50% rule in memory management?

50% of memory is lost to fragmentation.

A page number is represented by 10 bits. How many entries are in the page table?

2¹⁰

A 32-bit address is divided into 20 bits for the page number and 12 bits for the offset. ______ is the page number and ______ is the offset for the logical address 0x139A4BD7.

0x139A4, 0xBD7

paging

A common memory management scheme that avoids external fragmentation by splitting physical memory into fixed-sized frames and logical memory into blocks of the same size called pages.

frames

Fixed-sized blocks of physical memory.

page

A fixed-sized block of logical memory.

page number

Part of a memory address generated by the CPU in a system using paged memory; an index into the page table.

p

Part of a memory address generated by the CPU in a system using paged memory; an index into the page table.

page offset

Part of a memory address generated by the CPU in a system using paged memory; the offset of the location within the page of the word being addressed.

d

Part of a memory address generated by the CPU in a system using paged memory; the offset of the location within the page of the word being addressed.

page table

In paged memory, a table containing the base address of each frame of physical memory, indexed by the logical page number.

huge pages

A feature that designates a region of physical memory where especially large pages can be used.

frame table

In paged memory, the table containing frame details, including which frames are allocated, which are free, total frames in the system, etc.

page-table-base register (PTBR)

In paged memory, the CPU register pointing to the in-memory page table.

translation look-aside buffer (TLB)

A small, fast-lookup hardware cache used in paged memory address translation to provide fast access to a subset of memory addresses.

TLB miss

A translation look-aside buffer lookup that fails to provide the address translation because it is not in the TLB.

wired down

A term describing a TLB entry that is locked into the TLB and not replaceable by the usual replacement algorithm.

address-space identifier

A part of a TLB entry that identifies the process associated with that entry and, if the requesting process doesn't match the ID, causes a TLB miss for address-space protection.

ASIDs

A part of a TLB entry that identifies the process associated with that entry and, if the requesting process doesn't match the ID, causes a TLB miss for address-space protection.

flush

Erasure of entries in, e.g., a TLB or other cache to remove invalid data.

hit ratio

The percentage of times a cache provides a valid lookup (used, e.g., as a measure of a TLB's effectiveness).

effective memory-access time

The statistical or real measure of how long it takes the CPU to read or write to memory.

valid-invalid

A page-table bit indicating whether a page-table entry points to a page within the logical address space of that process.

segmentation

memory organization method dividing computer memory into segments, each with its own distinct address space

segment table length register (STLR)

a register that indicates the number of segments used by a program

segment table base register (STBR)

a register that holds the address of the segment table in memory

segment number

part of a logical address that specifies the segment in the segment table

segment table

a table that maintains information about each segment, including the base address and the limit

segmented paging

a memory management technique combining segmentation and paging, where segments are further divided into fixed-size pages

segment base address

the starting physical address of a segment in memory

segmented pages

memory management method using segments to organize data or code efficiently

segment offset

part of a logical address that specifies the position within a segment

swapped

Moved between main memory and a backing store. A process may be swapped out to free main memory temporarily and then swapped back in to continue execution.

backing store

The secondary storage area used for process swapping.

application state

A software construct used for data storage.

How does the translation look-aside buffer (TLB) enhance memory management in an operating system?

By speeding up address translation

What is the function of a page table in the context of paging?

To store frame addresses

How does segmentation improve memory management?

By allowing different segments

What is a limitation of segmentation in memory management?

It causes external fragmentation.

How does segmented paging enhance memory management compared to traditional segmentation?

By avoiding fragmentation

What role does a segment table play in segmented paging?

Stores segment bases

What is the purpose of swapping in memory management?

To move inactive processes

How does swapping differ in mobile systems compared to traditional systems?

Often not supported due to constraints

What is a backing store in the context of swapping?

Storage for swapped-out processes

How does swapping help in managing memory in a multitasking environment?

Handling more processes than physical memory