hw7

Caching

Storing copies of data at places that can be accessed more quickly.

Temporal Locality

Recently referenced locations are more likely to be referenced soon.

Spatial Locality

Reference locations tend to be clustered.

Cache Pollution

Leaving behind cache content with no localities.

Compulsory Misses

Data brought into the cache for the first time.

Capacity Misses

Caused by the limited size of a cache.

Write-through Caching Policy

Immediately propagates update through various levels of caching.

Write-back Caching Policy

Delays the propagation until the cached item is replaced.

Effective Access Time

The average time to access data through caches.

Demand Paging

Allowing pages that are referenced actively to be loaded into memory.

Page Fault

A referenced page is not in memory.

Belady's Anomaly

Adding more memory results in more page faults.

Thrashing

When the memory is overcommitted.

Working Set

Pages that are referenced within the past T seconds.

FIFO

A page replacement algorithm that services requests in the order they arrive.

MIN

A page replacement algorithm that replaces the page that will not be used for the longest time in the future.

LRU

Least Recently Used; replaces the page that has not been used for the longest period of time.

LFU

Least Frequently Used; replaces the page that is least frequently used.

Device Controller

Converting between serial bit stream and a block of bytes.

Device Driver

An OS component that hides the complexity of an I/O device.

Memory-mapped I/O

Making no distinction between device addresses and memory addresses.

Polling

A CPU repeatedly checks the status of a device.

Interrupt-driven I/Os

A device controller notifies the corresponding driver when the device is available.

Direct Memory Access

Using an additional controller to perform data movements.

Character Device

A device, like a keyboard, that handles data as a stream of characters.

Block Device

A device, like a disk, that handles data in fixed-size blocks.

FIFO Disk Scheduling

First-In-First-Out; services requests in the order they arrive.

SSTF Disk Scheduling

Shortest Seek Time First; services the closest request next.

SCAN Disk Scheduling

Serves requests in one direction until no more requests in that direction are left.

C-SCAN Disk Scheduling

Serves requests in one direction and then jumps back to the start.