Intro to Cache Memory

By david hsu

Examples of memory

• Paper and writing, books• Neon signs• Cassettes and other magnetic tape memory• Abacus• Art material such as clay, canvas, marble, rock,

etc.• Caves• The great pyramids• Our flesh (tattoos)

• ROM means read only memory and RAM means random access memory.

EPROMDDR2 RAM

CD ROM

PROM

FLASH MEMORY

RAM

• RAM allows you to read and write to it. Two basic forms of semiconductor random access memory: dynamic and static ram

RAM

• both RAMs use cells to store data

RAM

• DRAM’s cell is smaller than static ram cells so a DRAM is denser. it is created with capacitors and is written with information by storing charge in the capacitors. to keep the data in a DRAM cell, the capacitors must be constantly recharged periodically or refreshed periodically because the charge in them runs out. when it is being read, the charge in the capacitor gets discharged and needs to be recharged (also called volatile). it is used for main memory.

RAM

• SRAM is faster and more expensive than dram so it is used for cache memory. it is different from DRAM in that its charge does not need to be refreshed constantly in order for the memory to be kept (also called nonvolatile).

RAM

• when memory is saved, bits are set to either 1 or 0, 1 is written, 0 is empty. When read, the data needs to be refreshed.

ROM

• Read only memory include: ROM, PROM, EPROM, EEPROM, FLASH MEMORY.

• they are all random access memory, even though they have different names.

ROM

• read only memory means that once you write on the memory you cannot immediately overwrite it.

CD ROM

ROM

• ROM does not need constant recharging of memory.

ROM

• EPROM, erasable programmable read only access memory, even though is read only, can be erased by ultraviolet light and rewritten. so essentially it is not really read only.

EPROM

ROM

• erasure of regular read only and programmable read only memory is not possible.

Advantages of memory types

• some advantages of other memory are as follows:• Programmable ROM is inexpensive, but can only be

written once. if even one bit is written incorrectly, you have to throw the whole thing away.

• flash memory is good in that erasing it only takes a few seconds.

• error correction in memory uses hamming code system. • other memory include synchronous dram, Rambus

dram, developed by Rambus and adopted by Intel for several of its processors, DDR SDRAM