Cache Memory, CMOS & Memory Access Times

Cache Memory

A cache (pronounced “cash”) is a small and very fast memory. It is designed to speed up the transfer of data and instructions. It is faster than RAM. The data and instructions that are most recently or most frequently used by CPU are stored in cache.

The data and instructions are retrieved from RAM when CPU uses them for first time. A copy of that data or instructions is stored in cache. The next time the CPU needs that data or instructions, it first looks in cache. If the required data is found there, it is retrieved from cache memory instead of main memory. It speeds up the working of CPU.

Types of Cache Memory

Different types of cache memory are as follows:

Level 1 (L1) Cache: It is also called primary or internal cache. It is built directly into
the processor chip. It has small capacity from 8 KB to 128 KB.

Level 2 (L2) Cache: It is slower than L1 cache. Its size is large i.e. from 64KB to 4MB. New processors contain advanced transfer cache on processor chip that is a type of
L2 cache. The common size of this cache is 256 KB.

Level 3 (L3) Caches: This cache is separate from processor chip on the motherboard. It exists on computer that use L2 advanced transfer cache.

Flash Memory

Flash memory is also called flash ROM or flash RAM. It is a type of nonvolatile memory. It can be erased electronically and reprogrammed. Many computer are using flash BIOS, Flash BIOS can be updated easily if required.

Flash memory chip stores data on handheld computers like cellular phones, digital cameras etc. Another type of flash memory is Flash memory cards that stores flash memory on a removable device instead of chip.

CMOS

CMOS stands for complementary metal-oxide-semiconductor. It stores configuration information of computer. The information include the type of disk drivers, keyboard and monitor, current date & time and other startup information required during booting process.

CMOS chip uses battery power to retain information even when the computer is turned off. The information in CMOS can be changed.

Memory Access Times

The amount of time required by the processor to read data, instructions and information from memory is called access time. Access time is defined by different types of terminologies that are as follows:

• Millisecond: It is one thousandth of a second. It is denoted by ms.
• Microsecond: It is one millionth of a second. It is denoted by us.
• Nanosecond: It is one billionth of a second. It is denoted by ns.
• Picosecond: It is one trillionth of a second. It is denoted by ps.
• Megahertz: It can be converted into nanoseconds by dividing it into 1 billion ns. It is denoted by MHz.