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1. Study of Memories
Types of Memory
Memory can be divided into two types, VolatileMemory and Non-Volatile Memory volatilememory temporarily
stores the It loses data as soon as the system supply is turned off. Non volatilememory stores data permanently
The different types of memory
Ram stand for Random Access Memory itis a semiconductor based memory where the CPU or the other hardware
devices can read and write data it temporarily stores the data and it volatilememory.
Rom stands for Read Only Memory. It stores the data permanently and it is a non- volatilememory. Itdoes not lose
the data even after the system turns off. As a result,ROM is a permanent data storage area.
PROM Stands for the Programmable Read Only Memory. It stores programs permanently and is a non-volatile
memory. Programming the ROM is sometimes referred to as burningand itrequires a special machinecalled a
device programmer or ROM burning.
EPROM stands for the Erasable Programmable Read Only Memory. Ultra- Violet rays can remove the programs
from this memory.
EEPROM stands for the Electrically Erasable Programmable Read Only Memory. Electrical signal removes the
programs from this memory.
SRAM stands for the Static Random Access Memory
It is a type of semiconductor memory itstores the data.As long as the power is supplied to the system. Once the
Power is turned off or is losttemporarily data stored in sramis lostsramuses six transistorsfor each memory.
DRAM Stands for the dynamic Random Access Memory
The lifetime of the data in dram is very short. Itis approximately for fou.milliseconds.Thedata in dram arestored
in memory cells.

2. Types of DRAM
Synchronous Dynamic Random Access Memory
SDRAM synchronizes the memory speed with the CPU clock speed.the speed the sdramon the speed of the cpu bus.
It is faster than Sramdram edo dram and vram memories.
Rambus Dynamic Random Access Memory
RDRAM is the fastest computer memory. It sends data very frequently on the dat bus and on very rcycleas a result,the
RDRAM memory gets the data transfer speed of 800 MHz.The video memory on the graphic accelerator cards
and tha cache memories use this chip.
Double data rate 1:
Receptor tyrosine kinesis (RTKs) play a key role in the communication of cells with their
microenvironment. These molecules are involved in the regulation of cell growth, differentiation and
metabolism. The protein encoded by this gene is a RTK that is widely expressed in normal and
transformed epithelial cells and is activated by various types of collagen. This protein belongs to a
subfamily of tyrosine kinas receptors with a homology region to the Dictyostelium disodium protein discoid
in I in their extracellular domain. Its autophosphorylation is achieved by all collagens so far tested (type I
to type VI). A closely related family member is the DDR2 protein. In situ studies and Northern-blot
analysis showed that expression of this encoded protein is restricted to epithelial cells, particularly in the
kidney, lung, gastrointestinal tract, and brain. In addition, this protein is significantly over-expressed in
several human tumors from breast, ovarian, esophageal, and pediatric brain. This gene is located on
chromosome 6p21.3 in proximity to several HLA class I genes. Alternative splicing of this gene results
Double data rate 2

3. DDR2 SDRAM is a double data rate synchronous dynamic random-access memory interface. It
superseded the original DDR SDRAMspecification, and has since been superseded by DDR3 SDRAM.
DDR2 DIMMs are neither forward compatible with DDR3 nor backward compatible with DDR In addition
to double pumping the data bus as in DDR SDRAM (transferring data on the rising and falling edges of
the bus clock signal), DDR2 allows higher bus speed and requires lower power by running the internal
clock at half the speed of the data bus. The two factors combine to produce a total of four data transfers
per internal clock cycle. With data being transferred 64 bits at a time, DDR2 SDRAMgives a transfer rate
of (memory clock rate) × 2 (for bus clock multiplier) × 2 (for dual rate) × 64 (number of bits transferred) / 8
(number of bits/byte). Thus with a memory clock frequency of 100 MHz, DDR2 SDRAM gives a maximum
transfer rate of 3200 MB/s.