Explain what cache is used for, making sure to cover each of the types of cache.

What will be an ideal response?

Student responses will vary, but should be drawn from the following information from the text.

Most of today's computers improve their processing times with cache, which is a temporary storage area. Two common types of cache are memory cache and disk cache.

Memory cache helps speed the processes of the computer because it stores frequently used instructions and data. Most personal computers today have two types of memory cache: Level 1 (L1) cache and Level 2 (L2) cache. Some also have Level 3 (L3) cache.

• L1 cache is built directly on the processor chip. L1 cache usually has a very small capacity.
• L2 cache is slightly slower than L1 cache but has a much larger capacity. Current processors include advanced transfer cache (ATC), a type of L2 cache built directly on the processor chip. Processors that use ATC perform at much faster rates than those that do not use it.
• L3 cache is a cache on the motherboard that is separate from the processor chip. L3 cache exists only on computers that use L2 advanced transfer cache.

When the processor needs an instruction or data, it searches memory in this order: L1 cache, then L2 cache, then L3 cache (if it exists), then RAM - with a greater delay in processing for each level of memory it must search. If the instruction or data is not found in memory, then it must search a slower speed storage medium, such as a hard disk or optical disc.