How cache increases computer speed?

Answer 1

: Cache (pronounced cash) memory is extremely fast memory that is built into a computer's central processing unit (CPU), or located next to it on a separate chip. : The disk cache is used to hold the most recently-accessed information from the hard disk. If you are using your PC for work that is hard-disk-intensive, you may benefit from increasing the size of your disk cache.The CPU uses cache memory to store instructions that are repeatedly required to run programs, improving overall system speed. The advantage ofcache memory is that the CPU does not have to use the motherboard's system bus for data transfer. Whenever data must be passed through the system bus, the data transfer speed slows to the motherboard's capability. The CPU can process data much faster by avoiding the bottleneck created by the system bus.

When the processor needs to read from or write to a location in main memory, it first checks whether a copy of that data is in the cache. If so, the processor immediately reads from or writes to the cache, which is much faster than reading from or writing to main memory.

The diagram on the right shows two memories. Each location in each memory has a datum (a cache line), which in different designs ranges in size from 8[1] to 512[2] bytes. The size of the cache line is usually larger than the size of the usual access requested by a CPU instruction, which ranges from 1 to 16 bytes. Each location in each memory also has an index, which is a unique number used to refer to that location. The index for a location in main memory is called an address. Each location in the cache has a tag that contains the index of the datum in main memory that has been cached. In a CPU's data cache these entries are calledcache lines or cache blocks.

Answer 2

Computer processors operate on the concept of a cycle, which is one hertz. For example, a 3.0 GHz processor has a cycle of 1/3 of a nanosecond (3 billion instructions per second). Modern system memory has an access time of about 100 nanoseconds. This means that, in the absence of any buffers, a modern processor would be idle about 99.7% of the time waiting on data.

The first layer of buffering is the lookahead buffer. It is accessible in one cycle, so it has a speed identical to the processor's speed (using 3.0 GHz, access time is 1/3 of a nanosecond). This buffer is enough for approximately 2 to 4 instructions, and is used to fill the pipeline on a processor. Once this buffer is empty, more data has to come from somewhere.

If we had a modern speed processor with no cache, just a buffer and system memory, this means that every 1 nanosecond, the processor would still be waiting 99 more nanoseconds for more data, or a 99% waiting time. As one can see, this is a small improvement. Adding cache is the trick to accessing more data faster.

L1 cache is very fast, and very expensive to manufacture, so most processors have 64k to 256k of this type of memory. That is enough for 1,000 to 4,000 instructions and pieces of data. L1 cache can be accessed in about 4 clock cycles, so if the lookup buffer is 4 instructions big, that means that the L1 cache can keep the lookup buffer full while it has data available. With just L1 cache, the processor can go for up to 33 nanoseconds, so the wait time for more memory is reduced from 99 nanoseconds to just 67 nanoseconds.

The L2 cache is slower, but still expensive to manufacture, and has a speed of about 10 clock cycles (3.3 nanoseconds). This cache can theoretically keep the L1 cache full as long as there are no "misses", and provides up to 8 MB of data, or about 1,000,000 instructions or pieces of data.

Using L2 cache provides up to 333 nanoseconds of data, meaning that the 100 nanoseconds needed to access system memory is no longer a bottleneck; the processor can utilize up to 100% of its processing time. Even 2MB of L2 cache provides nearly 67 nanoseconds of data.

All of this, of course, depends on the reliability of the cache algorithms, which are over 99% accurate. Cache misses cost the system the entire 100 nanoseconds of access time, and are therefore undesirable, as the CPU has to wait on that data.

Answer 3

When data is accessed frequently, your computer uses its memory cache to access the memory faster. Increasing disk cache can improve performance, especially if you are using your computer for disc-intensive work.

When using an internet browser, a browser cache is used to load pages that you access frequently faster. Clearing your browser's cache every once in a awhile will speed up browser performance because over long periods of browsing, a large amount of data is stored in the browser cache.

Answer 4

A CPU cache is a cache used by the central processing unit of a computer to reduce the average time to access memory it is different as compare to the main memory which is used to copy data from the secondary storage it store the data inside the page file and then take it from there as compare to cache memory it exists inside the cpu and directly gives the data to cpu to process the instructions lets see a figure which will make it more clear.

Answer 5

Computers usually have a fixed amount of usable memory (RAM). If a program is particularly complex, it may need to use a lot of the available RAM - this means it might slow the computer down while it empties and re-fills the RAM. Cashing unused space from the hard-drive simply gives the computer extra (temporary) memory it wouldn't automatically have - the extra memory gives it the facility to do more operations than it would normally be able to do - making it faster..

Answer 6

Cache is used to store frequently used data in RAM (Random Access Memory). That is, if certain data is cached because of its frequent use, such data is retrieved from auxiliary storage (usually a disk storage device) once and kept in RAM. Subsequent usage of the data does not require the system to go to the auxiliary storage but use the data that is "cached" in RAM. Data access from RAM is many magnitudes faster that accessing the same every time from disk which includes the mechanical arms moving to the correct data sector on the disk (data seek), retrieving the data, account for retry operations in case of parity errors etc., getting the read buffer ready and finally writing the data into the buffer.

Answer 7

To give one example, a cache is used by a computer to store parts of websites the user has visited. Should the user revisit a previously cached website, the computer brings forth the website from the cache, which is faster than downloading the entire website from the internet.

Answer 8

Because in reduces the time required to process data by eliminating an intermediate process.