Cache Replacement Policy

The cache replacement policy is the technique for choosing which cache block to replace when a fully associative cache is full,or when a set associative cache's line is full.One thing that you must note here is their is no choice in a direct-mapped cache that is a main memory address always maps to the same cache address and thus replaces whatever block is ready there.There are three common replacement policies for the cache.The first one is random replacement policy that chooses the block to replace randomly.While simple to implement,this policy does nothing to prevent replacing a block that is likely to be used soon.

The second replacement policy is least recently used(LRU) replacement policy replaces the block that has not been accessed for the longest time,assuming that this means that it is least likely to be accessed in near future.This technique provides for an excellent hit/miss ratio but requires expensive hardware to keep track of the times blocks are accessed.The third and last replacement policy is first in first out replacement policy uses a queue size N,pushing each block address onto the queue when the address is accessed,and then choosing the block to be replaced by popping the queue.

Cache Memory

As all we know that,processing core and the memory are two integral parts of any CPU(Central Processing Unit).Now further this,memory is again divided into two categories slow memory and fast memory.Slow memory are RAM and hard disk,while Cache memory is the fast memory.The term slow and fast directly implies with the speed with which data can be accessed from these memory units.In simple words we can say cache memory is the memory that is used to store frequently used data so that the CPU doesn't have to wait for the data to be fetched from another slower storage areas like the system RAM or hard disk.

The main reason behind the fast accessing of data from cache memory is that it does not require refreshing of data and it is made of quite expensive static RAM.Once the data is stored in the cache, future use can be made by accessing the cached copy rather than re-fetching or re-computing the original data and this is what makes the average access time shorter. Cache, therefore, helps expedite data access that the CPU would otherwise need to fetch from main memory. The main advantage of cache memory is that performance of the CPU is increased to a great extent and it saves use of the read/write head which in turn extends its life too.Now a days cache memory is available in the range from 2 MB to 16 MB.

Understanding BIOS/CMOS

Though often interchangeably used, the two terms refer to different things. BIOS(Basic Input Output System) refers to asset of instructions that are critical for the functioning of the system .These instructions include information about the components connected to the motherboard, like the hard disk, RAM, and the configuration of the many onboard subsystems .CMOS (Complementary Metal Oxide Semiconductor) refers to the chip on which the BIOS instructions are stored. CMOS is the name of the technology behind the chip that stores the BIOS.Present-day CMOS is technically called EEPROM for Electronically Erasable Programmable Read-only Memory.These can be rewritten too, and this allows the BIOS instructions of a motherboard to be updated when required. The process of updating the BIOS instructions is called Flashing.

Flash Memory

Flash Memory is the type of memory which is non-volatile in nature which means that it does not need power to maintain the information stored in the chip and primarily used in memory cards and USB flash drives for generals storage of data.You can also use these devices for transfer of data between computers and other digital products.The main advantage of using a flash drive is that it can be electrically erased and reprogrammed.Now if talk about the internal components of a flash drive then flash drive consists of a Flash Memory chip that stores the data, a controller that manages the read/write operations, and a USB interface.Now a days flash memory is also available as in non integrated form that means it can be plugged into Memory Card readers that have a USB interface.If we take a look at the advantages of the flash drives then it offers you fast read access times and better kinetic shock resistance than hard disks.In addition to this, when the flash memory is packaged in a memory card then it offers you very high durability,able to withstand intense pressure, extremes of temperature, and immersion in water.

Bad Sectors

As all we know that a hard drive is made of the millions of sectors and it is possible that some of these sectors gone bad.As I a want to told you that when a hard drive is manufactured it still contains some bad sectors and as the life span of hard drive's increase or it gets old the number of bad sectors increased in it.A sector is a small area on the surface of the hard drive or a floppy disk.As all we know that each hard drive have several platters.The platters are the disc that are covered with magnetic material which is used to hold data and they are divided into a number of concentric rings known as track.If we talk about a floppy disk(1.44 MB) than it contains only one platter and having about 160 tracks.But in the case of hard drive it contains a lot of tracks and each track is divided into smaller storage areas called sectors.Now when a sector goes bad the whole data that it contains lost and it cannot be recovered.Bad sectors never affects the data of the remaining hard disk and disk is still completely usable.The main problem with the bad sectors is that it cannot be repaired,it only marked as unusable.Once you marked these bad sectors as unusable then operating system will never store data in these areas and storage capacity of your hard drive is decreased.