The area in an L2 cache that identifies which data from main memory is currently stored in each cache line. The actual data is stored in a different part of the cache, called the data store. The values stored in the tag RAM determine whether a cache lookup results in a hit or a miss.
The size of the data store determines how much data the cache can hold at any one time. The size of the tag RAM determines what range of main memory can be cached. Many modern PCs, for example, are configured with a 256K L2 cache and tag RAM that is 8 bits wide. This is sufficient for caching up to 64 MB of main memory. If you add additional main memory, however, it won’t be cached unless you also expand tag RAM. Some motherboards allow you to add additional tag RAM chips for this purpose but many do not.
For Pentium Pro and Pentium II microprocessors, the tag RAM is integrated in the chipset. Pentium Pros have an integrated L2 cache capable of caching up to 4 GB of main memory. Pentium IIs use a SEC daughtercard for L2 caches and can cache up to 512 MB.
(1) Commonly used in blogs, site authors attach keyword descriptions (called tags) to identify images or text within their site as a categories or topic. Web pages and blogs with identical tags can then be linked together allowing users to search for similar or related content. If the tags are made public, online pages that […]
- tag cloud
) [Image: Screenshot showing a visual representation of a tag cloud. This image shows the “All time most popular tags” from Flickr Photo Sharing] A tag cloud is a stylized way of visually representing occurrences of words used to described tags. The most popular topics are normally highlighted in a larger, bolder font. Visitors to […]
- tape drive
A device, like a tape recorder, that reads data from and writes it onto a tape. Tape drives have data capacities of anywhere from a few hundred kilobytes to several gigabytes. Their transfer speeds also vary considerably. Fast tape drives can transfer as much as 20MB (megabytes) per second. The disadvantage of tape drives is […]
A magnetically coated strip of plastic on which data can be encoded. Tapes for computers are similar to tapes used to store music. Storing data on tapes is considerably cheaper than storing data on disks. Tapes also have large storage capacities, ranging from a few hundred kilobytes to several gigabytes. Accessing data on tapes, however, […]
(1) Short for tape archive, a UNIX utility that combines a group of files into a single file. The resulting file has a .tar extension. The tar command does not compress files. Frequently, therefore, a tar file is compressed with the compress or gzip commands to create a file with a .tar.gz or .tar.Z extension. […]