Explain Cache Operation.

Explain cache operation.

CPU cache

Hardware implements cache as a block of memory for temporary storage of data likely to be used again. Central processing units (CPUs) and hard disk drives (HDDs) frequently use a cache, as do web browsers and web servers.
A cache is made up of a pool of entries. Each entry has associated data, which is a copy of the same data in some backing store. Each entry also has a tag, which specifies the identity of the data in the backing store of which the entry is a copy.
When the cache client (a CPU, web browser, operating system) needs to access data presumed to exist in the backing store, it first checks the cache. If an entry can be found with a tag matching that of the desired data, the data in the entry is used instead. This situation is known as a cache hit. So, for example, a web browser program might check its local cache on disk to see if it has a local copy of the contents of a web page at a particular URL. In this example, the URL is the tag, and the contents of the web page is the data. The percentage of accesses that result in cache hits is known as the hit rate or hit ratio of the cache.

Disk cache

A disk cache is a mechanism for improving the time it takes to read from or write to a hard disk. Today, the disk cache is usually included as part of the hard disk. A disk cache can also be a specified portion of random access memory (RAM). The disk cache holds data that has recently been read and, in some cases, adjacent data areas that are likely to be accessed next. Write caching is also provided with some disk caches.

Comments

Define Swapping technique which is usually used in memory management

Define Swapping technique which is usually used in memory management Swapping is a simple memory/process management technique used by the operating system(os) to increase the utilization of the processor by moving some blocked process from the main memory to the secondary memory(hard disk);thus forming a queue of temporarily suspended process and the execution continues with the newly arrived process. After performing the swapping process, the operating system has two options in selecting a process for execution Swapping is a mechanism in which a process can be swapped temporarily out of main memory to a backing store , and then brought back into memory for continued execution. Backing store is a usually a hard disk drive or any other secondary storage which fast in access and large enough to accommodate copies of all memory images for all users. It must be capable of providing direct access to these memory images. Major time cons...

Operating Systems Definition and the Classification of OS

OPERATING SYSTEMS ( OS ) What is an operating system? An operating system (sometimes abbreviated as "OS") is the program that, after being initially loaded into the computer by a boot program, manages all the other programs in a computer. The other programs are called applications or application programs. The application programs make use of the operating system by making requests for services through a defined application program interface (API). In addition, users can interact directly with the operating system through a user interface such as a command language or a graphical user interface (GUI). An operating system performs these services for applications: In a multitasking operating system where multiple programs can be running at the same time, the operating system determines which applications should run in what order and how much time should be allowed for each application before g...

3.1.1 Identify Between Resident And Transient Routines

Memory Management Memory management is concerned with managing: The computer’s available pool of memory Allocating space to application routines and making sure that they do not interfere with each other. 3.1.1 Identify between resident and transient routines The operating system is a collection of software routines. Resident routines Transient routines Routines that directly support application programs as they run Stored on disk and read into memory only when needed Example: routine that control physical I/O Example: routine that formats disks The operating system occupies low memory beginning with address 0. Key control information comes first followed by the various resident operating system routines. The remaining memory, called the transient area, is where application programs and transient operating system routines are loaded. Resident & transient routines structure...

learningoperatingsystem

Search This Blog