Common PC Major RAMs

Memory is supplied in modules a small circuit boards which we plug into the motherboard in special sockets. There are two type of RAM modules

• SRAM – Static Random Access Memory - is a type of semiconductor memory. The word "static" indicates that the memory retains its contents as long as power remains applied, unlike dynamic RAM (DRAM) that needs to be periodically refreshed.SRAM does not use capacitors to store 1s and 0s. Instead, SRAM uses a special circuit called a flip-flop. The advantages of SRAM are that it is fast and it does not have to be refreshed because it uses the flip-flop circuit to store each bit. A flip-flop circuit will toggle on or off and retain its position, whereas a standard memory circuit requires constant refreshing to maintain an on state. The main disadvantage of SRAM is that it is more expensive than DRAM.

• DRAM – Dynamic Random Access Memory - Because of this refresh requirement, it is a dynamic memory as opposed to SRAM and other static memory. - DRAM works by using a microscopic capacitor and a microscopic transistor to store each data bit. A charged capacitor represents a value of 1, and a discharged capacitor represents a value of 0. A capacitor works like a battery—it holds a charge and then releases it. Unlike a battery, which holds a charge for months, the tiny capacitors in DRAM hold their charges for only fractions of a second. Therefore, DRAM needs an entire set of circuitry just to keep the capacitors charged. The process of recharging these capacitors is called refreshing. Without refreshing, the data would be lost. This is another reason DRAM is called volatile memory. - DRAM Is most commonly used as the main memory - DRAM - the main memory in many Pentium computers

Memory usually has to be present in multiples of 4 units. That is the smallest amount of RAM that a PC can effectively use is 4mb. Common multiples are 16Mb. 32Mb, 64Mb128Mb etc. the more megabytes of RAM a PC has the faster it is able to process information. .

. Most Common DRAM used in PC’s are:

Synchronous Dynamic RAM (SDRAM) 1. Single Data Rate (SDR) SDRAM is a synchronous form of DRAM. 2. Double data rate (DDR) SDRAM was a later development of SDRAM, used in PC memory from 2000 onwards. DDR2 SDRAM is a minor enhancement on DDR-SDRAM that mainly affords higher clock speeds and somewhat deeper pipelining.