Learn about computer Memory

1. Types of RAM
SRAM(Static RAM)
 It retains stored information only when the power supply is on. It is used for
cache memory.
 They have higher speed.
 Static RAM is costlier and also consume more power.
 RAM is used to create the CPU’s speed sensitive cache.

2. DRAM
 Dynamic RAM is used on a single and dual in-line memory modules. It is one of the most
type of RAM.
 Dynamic RAM has to be dynamically refreshed all of the time. The downside of all of this
refreshing is that it takes time and slows down the memory.
 D-RAM’s are cheaper & lower as compared to static RAM.

3. SDRAM
 Synchronous Dynamic Random Access Memory
 Synchronous DRAM run at high clock speed and is synchronized with the CPU bus.
 SDRAM was originally packaged on a 168-pin DIMM.
DRDRAM
 Direct Rambus Dynamic Random Access Memory
 Direct Rambus DRAM is implemented with RIMM memory module.
 It is a type of synchronous, dynamic RAM

4. DDR SDRAM
 Double Data Rate SDRAM transfers data twice per clock cycle. The transfer rate of the data
becomes doubles.
 Use additional power and ground lines and is packaged on a 184-pin DIMM module.
DDR2 SDRAM
 DDR2 chip increase the data rate over those of DDR chips. DDR2 modules require 240-pin
DIMM slots.
 DDR2 chips will not fit into DDR slots although having same length of DDR.
DDR3 SDRAM
 DDR3 chips transfer data at twice the rate that of DDR2 and consume less power in the
process.
 DDR3 also required 240-pin DIMM slot but cannot be used interchangeable since electrical
requirement and notch location are different.

5. DDR SDRAM
DDR2 SDRAM

6. DDR4 SDRAM
 Double Data Rate fourth generation synchronous dynamic random-access memory the
latest variant of memory in computing.
 DDR4 is able to achieve higher speed and increased transfer rates and decreased
voltage.
 DDR4 chip support transfer rates between 2133 MT/s (million transfers per second)
and 4266 MT/s whereas DDR3 technology supports only up to 800 to 2133 MT/s.
 Storage capacity ranges from 4 – 128 GB/DIMM

7. Types of ROM
(i) PROM(Programmable ROM).
 PROM is a memory chip on which you can store a program
 Once the PROM has been used you cannot wipe it clean and use it to store something
 A memory chip that can be changed only once.

8. (ii) EPROM(Erasable and programmable read only memory)
 An EPROM is an erasable PROM. The stored data in EPROM’s can be erased by exposing it
to UV light for about 20 min.
 It’s not easy to erase it because the EPROM IC has to be removed from the computer and
exposed to UV light.
 The entire data is erased and not selected portions by the user. EPROM’s are cheap and
reliable.

9. (iii) EEPROM (Electrically erasable and programmable ROM)
 Electrically Erasable PROM that the chip can be erased & reprogrammed on the board
easily byte by byte.
 It can be erased with in a few milliseconds.
 There is a limit on the number of times the EEPROM’s can be reprogrammed, i.e.; usually
around 10,000 times.

10. Memory selection tips
The consideration one should know while selecting the memory on your system
Size: Find out the maximum size of the memory module that your computer supports. Do
not find module larger than what your motherboard memory slots can each accommodate.
Speed: Find out what is the current speed of the RAM in the computer. What is the bus
speed of the computer. RAM speed is the time needed to read and recharge a memory cell,
and is measured in nanosecond. A nanosecond is one-billionth of a second. So, smaller the
number, faster the RAM.
System board configuration: Determines which of the four type of RAM your system
uses. Most machine supports only one type of RAM and have one type of module or
connector.