Webopedia on Google+Webopedia on TwitterWebopedia on FacebookTech Bytes Blog
Main » TERM » S »

snooping protocol

(n.) Also referred to as a bus-snooping protocol, a protocol for maintaining cache coherency in symmetric multiprocessing environments. In a snooping system, all caches on the bus monitor (or snoop) the bus to determine if they have a copy of the block of data that is requested on the bus. Every cache has a copy of the sharing status of every block of physical memory it has. Multiple copies of a document in a multiprocessing environment typically can be read without any coherence problems; however, a processor must have exclusive access to the bus in order to write.

Snooping Protocol Types

There are two main types of snooping protocol:

Write-invalidate

The processor that is writing data causes copies in the caches of all other processors in the system to be rendered invalid before it changes its local copy. The local machine does this by sending an invalidation signal over the bus, which causes all of the other caches to check for a copy of the invalidated file. Once the cache copies have been invalidated, the data on the local machine can be updated until another processor requests it.

Write-update

The processor that is writing the data broadcasts the new data over the bus (without issuing the invalidation signal). All caches that contain copies of the data are then updated. This scheme differs from write-invalidate in that it does not create only one local copy for writes.







TECH RESOURCES FROM OUR PARTNERS
DID YOU KNOW?
What You Don't Read Can Hurt You

Does this sound familiar? An online service promises to help your small business cut costs, increase productivity, make your coffee and walk your... Read More »

Who's Moving Ahead in Cloud Computing?

The future remains, well, cloudy. But either way: Amazon, look out. Microsoft is gaining fast. Read More »

We Can't Give Up on Privacy!

Even new and emerging technologies that can make our lives easier, safer and healthier can jeopardize our privacy. Read More »

QUICK REFERENCE
Webopedia Polls

The trend for the past two years has been for shoppers to spend more online during the holiday season. How do you typically shop for holiday... Read More »

How to Create a Desktop Shortcut to a Website

This Webopedia guide will show you how to create a desktop shortcut to a website using Firefox, Chrome or Internet Explorer (IE). Read More »

Flash Data Storage Vendor Trends

Although it is almost impossible to keep up with the pace of ongoing product releases, here are three recent highlights in the flash data storage... Read More »