What is RAM ?

Random Access Memory (RAM):-

RAM

• RAM is an acronym for random access memory, a type of computer memory that can be accessed randomly; any byte of memory can be accessed without touching the preceding bytes.
• RAM is the most common type of memory found in computers and other devices.
• Random-access memory is a form of computer data storage.
• It is a type of a volatile memory and therefore it is referred to as a temporary data storage area.

Types of RAM:-

1. Static RAM

SD RAM

SD RAM

• Static random-access memory (SRAM) is a type of semiconductor memory that uses bistable latching circuitry to store each bit.
• It is referred to as static because of the fact that it does not require refreshing like Dynamic RAM.
• Static RAM store data as long as power is supplied to the system.
• This is because Static RAM is made up of transistor that do not require refreshing.
• It is used as a computer system cache memory.

2. Dynamic RAM

DDR RAM

• Dynamic RAM is a type of RAM that stores each bit of data in a separate capacitor within an integrated circuit.
• The capacitor can be either charged or discharged; these two states are taken to represent the two values of a bit, conventionally called 0 and 1.
• Since even non-conducting transistors always leak a small amount, the capacitors will slowly discharge, and the information eventually fades unless the capacitor charge is refreshed periodically.
• Because of this refresh requirement, it is a dynamic memory as opposed to SRAM and other static memory.

Other Different Types of RAM:-

i) EDO RAM (Extended Data-Out DRAM)

• EDO DRAM, sometimes referred to as Hyper Page Mode enabled DRAM, is similar to Fast Page Mode DRAM with the additional feature that a new access cycle can be started while keeping the data output of the previous cycle active.
• This allows a certain amount of overlap in operation (pipelining), allowing somewhat improved performance.
• It was 5% faster than FPM DRAM, which it began to replace in 1995, when Intel introduced the 430FX chipset that supported EDO DRAM.

    ii) FPM RAM (First Page Mode DRAM)    

• Fast page mode dynamic random access memory was the original form of DRAM.
• It waits through the entire process of locating a bit of data by column and row and then reading the bit before it starts on the next bit.
• Maximum transfer rate to L2 cache is approximately 176 MBps.

   iii) SDRAM (Synchronous Dynamic RAM)

• SD RAM takes advantage of the burst mode concept to greatly improve performance.
• It does this by staying on the row containing the requested bit and moving rapidly through the columns, reading each bit as it goes.
• The idea is that most of the time the data needed by the CPU will be in sequence.
  
  
•  SDRAM is about five percent faster than EDO RAM and is the most common form in desktops today.
• Maximum transfer rate to L2 cache is approximately 528 MBps.
  

iv) DDR SDRAM (Double Data Rate SD RAM)

• DDR RAM is just like SDRAM except that is has higher bandwidth, meaning greater speed.
• Maximum transfer rate to L2 cache is approximately 1,064 MBps (for DDR SDRAM 133 MHZ).

v) RDRAM(Rambus Dynamic RAM)

• Rambus dynamic random access memory is a radical departure from the previous DRAM architecture.
• Designed by Rambus, RDRAM uses a Rambus in-line memory module (RIMM), which is similar in size and pin configuration to a standard DIMM.
• What makes RDRAM so different is its use of a special high-speed data bus called the Rambus channel.
• RDRAM memory chips work in parallel to achieve a data rate of 800 MHz, or 1,600 MBps.
• Since they operate at such high speeds, they generate much more heat than other types of chips.
• To help dissipate the excess heat Rambus chips are fitted with a heat spreader, which looks like a long thin wafer.
• Just like there are smaller versions of DIMMs, there are also SO-RIMMs, designed for notebook computers.

vi) Credit Card Memory

• Credit card memory is a proprietary self-contained DRAM memory module that plugs into a special slot for use in notebook computers.
  

vii) PCMCIA Memory Card

•  Another self-contained DRAM module for notebooks, cards of this type are not proprietary and should work with any notebook computer whose system bus matches the memory card's configuration.

   

viii) CMOS RAM

• CMOS RAM is a term for the small amount of memory used by your computer and some other devices to remember things like hard disk settings
• This memory uses a small battery to provide it with the power it needs to maintain the memory contents.

ix) VRAM

•  Video RAM, also known as multiport dynamic RAM (MPDRAM), is a type of RAM used specifically for video adapters or 3-D accelerators.
• The "multiport" part comes from the fact that VRAM normally has two independent access ports instead of one, allowing the CPU and graphics processor to access the RAM simultaneously.
• VRAM is located on the graphics card and comes in a variety of formats, many of which are proprietary.
• The amount of VRAM is a determining factor in the resolution and color depth of the display. VRAM is also used to hold graphics-specific information such as 3-D geometry data and texture maps.
• True multiport VRAM tends to be expensive, so today, many graphics cards use SGRAM (synchronous graphics RAM) instead.
• Performance is nearly the same, but SGRAM is cheaper.

Difference between Static RAM and Dynamic RAM:

Static RAM	Dynamic RAM
Store data till power is switched off	Store data for few mille second.
Use set of transistor for each memory cell	Use single transistor and capacitor for each memory cell.
Does not refresh memory cell	Need to refresh memory cell
Data access is faster	Data access is slower
More power	Less Power
Expensive	Less Expensive

DDR 1	DDR 2	DDR 3	DDR 4
It has 186 pins and the speed of this RAM is 400 MHz	It has 240 pins and the speed of this RAM is 800 Mhz.	It has 240 pins and the speed of this RAM is 1066 MHz	It has 240 pins and the speed of this RAM is 2133 MHz
It require around 2.5v.	It require around 1.8v to 2.2v.	It require around 1.5v to 1.65v.	It require around 1.2v

  Memory Packages:

• It is a small circuit board that contains memory chips.
• SIMM, DIMM, SODIMM and RIMM are some of the memory packages.
• These package are the form factors of a RAM chip.
• The installation of a memory depends on the form factors of a RAM.
• A form factors is the size and shape of the memory packages.

 Types of Memory Packages:

   1.     SIMM (Single In-line Memory Module) :

• SIMM is a small circuit board designed to hold memory chips.
•  It contains pins for accepting data from the control circuit. These circuit boards or modules are known as packages.
• There are various SIMM packages available based on the number of pins it contains.
• For example, there are 30-pin packages and 72-pin packages.

  2.   DIMM (Dual In-line Memory Module):

• DIMM package is also a small circuit board that contains the memory chips.
• The difference between the SIMM and DIMM is that DIMM is a 168-pin package.
• The data widths of the DIMM packages are 64-bit, 72-bit, or 80-bit.
• A 168-pin DIMM package is available in the SDRAM or FPM DRAM chips.

  3.   SODIMM (Small In-line Memory Module):

• Laptops and notebook systems use this package.
• It is the smallest version of the DIMM. The SODIMM package has a notch at the bottom of the circuit board.
• This notch helps in inserting the SODIMM package in the memory socket.
• SODIMM packages are available with 144 and 200 pins.
• A 144-pin SODIMM package has 64-bit data path.
• The FPM DRAM and EDO DRAM use this package.
• The 72 pins on both the sides of the package divide a 144-pin package.

  4.   Micro DIMM

• Micro DIMM stands for Micro Dual Inline Memory Module.
• This package is smaller than DIMM and SODIMM packages.
  
  
• The sub-notebook systems use these memory packages.
• The Micro DIMM package pins connect the memory module with the memory socket.
• These pins provide communication lines for the module and the system.
• This package does not have the notch at the bottom.
• Micro DIMM packages are available with 144 and 172 pins.

  5.   RIMM

• RDRAM chip uses the RIMM memory package.
• This package is same as the DIMM package.
• It only differs in the pin configuration.
• The high bandwidth and the low latency applications use this in this memory package.
• The RIMM package has a data storage speed of 600 MHz, 711 MHz, 800 MHz, and 1066 MHz