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RAM of a Computer : Definition, Types and Form Factors

Updated on January 1, 2014
Example of DDR SDRAM
Example of DDR SDRAM

RAM is an acronym for Random access memory. It is otherwise known as the primary memory of the computer and the hard drive is the secondary memory for bulk storage. The RAM of a computer is a memory that can be accessed randomly when the system is in use. It is a temporary memory for information storage because when there is power outage, the information goes and even when the computer is in use if not refreshed.

Going by the rule of thumb, the higher a computer memory, the greater its speed and vice versa. This knowledge is vital when purchasing a computer system and at least with a fair knowledge of the purpose the computer will serve. It is pertinent to state that computer motherboard has peculiar memory (RAM) it supports base on the motherboard Form factors. This will be discussed as we progress.

There are different types of computer RAM (Random Access Memory). The type of RAM a computer motherboard supports depend on the speed of the front side bus of its architecture. The front side bus of the motherboard architecture is the signal pathway between the computer processor and the memory. It houses the fastest chipsets (in terms of speed) of the motherboard circuitry and evidently the most important chipsets in the entire circuitry.

Types of RAM of a Computer

Broadly speaking there are two types of of a computer RAM( Random Access Memory). These are the Dynamic Random Access Memory (DRAM) and the Static Random Access Memory (SRAM). Anytime you here any discuss on the RAM of a Computer, it has to do with any of these two and their derivatives. Static RAM is not so popular because it is very expensive to develop and maintain. So this discourse will focus more on Dynamic RAM and its derivatives.

As indicated earlier the dynamic random access memory is use to describe the dynamic nature of the memory a situation when it retain its information only when refreshed constantly (called refresh signal), otherwise the information will go. Static RAM (SRAM) does not need constant refresh signal to retain information on it. However, because of its bulky nature and other limitations it did not gain popularity. Below are DRAM peculiarities and it derivatives.


FPM DRAM: FPM DRAM stands for Fast Page Mode Dynamic Random Access Memory. This came up with the early history of DRAM. It accesses a bit as a single task and finishes with it before accessing the next one. It operated at 176 MBPs.

EDO DRAM: EDO DRAM is an acronym for Extended Data-Out Dynamic Access Memory. EDO DRAM was an improvement on FPM DRAM as it does not need to wait for one single task to finish processing before accessing the next one. As soon as it commences the processing one bit, it starts accessing the next one immediately. This brought about greater speed and efficiency as compared with FPM DRAM. It operates at approximately 264MBPs.

SDRAM: SDRAM is an acronym for Synchronous Dynamic Random Access Memory. The initial DRAM uses asynchronous interface as it operates independent of the Processor. This was not good enough with respect to efficiency as computer usage kept growing in complexity and functions. It could not measure up with the demand placed on it by the processor. This challenge led to the emergence of SDRAM in the mid 1990s.

SDRAM synchronizes data between it and the processor concurrently thereby creating a continuous sequence of data processing with each carried out in turn. SDRAM runs at 133MHz, this was twice faster than EDO DRAM and three times faster than FTP DRAM. The major drawback of SDRAM was that it operates on Single Data Rate (SDR). This means it can only perform a single task per clock circle. This does not go well with contemporary demand in terms of computer speed. This led to the birth of Double Data Rate SDRAM (DDR SDRAM).

DDR SDRAM: As indicated from the foregoing, the Double Data Rate SDRAM was developed to solve the apparent shortcoming of Single Data Rate SDRAM. As the name implies, DDR SDRAM is able to move data at a speed faster than it immediate predecessor with a lesser energy consumption (2.5 volts) and up to 200400 MTPs. This was a great feat in the World of Computing. However as technology grows and higher Processor emerges, this became inadequate. The DDR SDRAM has 184 Pins and eight RAM chips with the ninth empty.

In the year 2003, a greater technology emerges that saw the birth of Double Data Rate type2 (DDR2 SDRAM). This again doubled the speed of first generation DDR SDRAM. DDR2 Dynamic RAM form factor operates at 4001066 MTPs (at 200533 MHz base) as per the rate of data transfer and even with a lesser power consumption (1.8 volts).

A further development emerged in the year 2007, still in this regard that bought about the birth of DDR3 SDRAM serving as the current market standard as at the time of this discourse. DDR3 further doubled the speed of DDR2 and with a lesser power consumption. DDR3 SDRAM rate of data transfer is 8002133 MTPs and 1.5 volts power consumption. DDR4 is expected to be on board soon. DDR3 technology utilizes both rising and falling edges of the clock circle a cardinal factor that underlies its speed. It has up to 8GB capacity.

RAM of Computer
RAM of Computer | Source

RAM of a Computer Form Factors

The form factors of random access memory described their kind of design, position of chips, their sizes, their compatibility with expansion slots and motherboards. Computer industry is driven by standards and the essence of this is to make available components that will be compatible with existing systems irrespective of the manufacturer. The RAM of a computer commonest form factors are as follows:

SIMM: This is one of the earliest RAM form factor. It is an acronym for Single Inline Memory Module (SIMM) that was used in the 1980s up to 1990s. The DIP Chips on the motherboard circuitry of the early computers occupies an unnecessary larger space more than what is obtainable today. It was then conceived that a small circuit board could be designed where such chips can be integrated for space economy and greater efficiency. More so, such boards can easily be removed.

SIMM has all the chips placed on one side of the Printed Circuit Board (PCB). Four SIMMs can be arranged in one row or space where the DIP chips hitherto occupies. The earliest set of Single Inline Memory Module has nine DIP chips integrated on the board and placed vertically very close to each other on their slots. This was a measure geared towards minimizing chips creep. Most SIMMs is 32-bit with 256kb to 1MB capacity.

If a Processor is 64-bit and SIMM is 32-bit, one most necessarily install more than one SIMM or change to Dual Inline Memory Module (DIMM) which will be discussed as we progress. This account for why more than one SIMMs is found on system boards. The first sets of SIMM came with nine DIP chips and with 30 pins (conductors) that interface via their slots with the motherboard circuitry. This was replaced with 72 Pins later in the 1990s.

DIMM: DIMM is an acronym for Dual Inline Memory Module. Unlike the SIMM, the DIMM form factor is 64-bit and has seen a remarkable growth since its birth. It came with RAM chips on both sides and 168 pins (conductors) during launch. DIMMS Slots is usually black while those of SIMM are white in colour. The shortcoming of SIMM form factor led to the birth of DIMM. Instead of installing more than one SIMM due to higher processor bytes, DIMM is preferred and performed better.

The conductors on DIMM are electrically isolated making separate contacts contrary to SIMM that are tied together. A number of modifications has occurred and still in the making. DDR3 DIMM is 240 Pins and it is electrically incompatibles with its predecessors. DIMM have a number of derivatives whose offshoot is dominant in computing industry.

RIMM: This is computer RAM form factor that came with the introduction of Intel 850 chipsets for Pentium 4 systems. It came with 184 pins (conductors) .This was in connection with Rambus DRAM (RDRAM) technology. RIMM is not an acronym like SIMM but a trademark term chosen by Rambus to describe the type of memory module. Rambus DRAM (RDRAM) is a superior memory as compared with its predecessors that creates multiple communication pathways between the memory and the system processor. This brought about greater speed and better memory efficiency.

The Printed Circuit Board containing the RAM chips has aluminum sheet that covers it called heat spreaders to protect the RAM from overheating. RIMM was very expensive and so it did not gain popularity. Alongside with this technology was development of Small Outline RIMM (SO-RIMM) for notebooks and similar computers that use smaller components.

SO-DIMM: Laptops and Notebooks that use smaller components with respect to size don’t use standard RAM form factors such as DIMM and SIMM. SO-DIMM is an acronym that stands for Small outline Dual Inline Memory Module. The SO-DIMM came with 72 and 144 Pins (conductors) with 32-bit and 64-bit respectively. With the passage of time, just as computer motherboards form factors keep changing in line with technology and users demand, the same is applicable to RAM of computer form factors. We have SO-DIMM that is 204 Pins in line with DDR type 3. So when making choices especially for the sake of upgrade these variations should be noted

Micro DIMM: This is one of the smallest RAM form factors used by mini and ultra light notebooks. It uses 64-bit memory module and the first set came with 164 Pins.

The foregoing reveals a phenomenal growth in computer Memory (RAM of a Computer) technology especially in the past two decades. Developers and manufacturers of computer components cannot rest on their oars at any level of achievement at any point in time. Because, growth and improvement in one aspect of the system technology, will invariably require others to follow suit.


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      António Cardoso 2 years ago

      Thanks a lot! The articule is very good and helped me a lot! You made me a Work! :p

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      aminsi waiswa 17 months ago

      The foregoing reveals a phenomenal growth in computer Memory (RAM of a Computer) technology especially in the past two decades. Developers and manufacturers of computer components cannot rest on their oars at any level of achievement at any point in time. Because, growth and improvement in one aspect of the system technology, will invariably require others to follow suit.

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