A
Memory divider is a ratio which is used to determine the operating clock
frequencyFrequency is the number of occurrences of a repeating event per unit time. It is also referred to as temporal frequency.The period is the duration of one cycle in a repeating event, so the period is the reciprocal of the frequency....
of
computer memoryComputer memory refers to devices that are used to store data or programs on a temporary or permanent basis for use in an electronic digital computer. Computers represent information in binary code, written as sequences of 0s and 1s...
in accordance with
Front Side BusIn personal computers, the front side bus is the bus that carries data between the CPU and the northbridge.Depending on the processor used, some computers may also have a back-side bus that connects the CPU to the cache...
frequency, if memory system is dependent on FSB clock speed. Along with memory latency timings, memory dividers are extensively used in
overclockingOverclocking is the process of running a computer component at a higher clock rate than it was designed for or was specified by the manufacturer, usually practiced by enthusiasts seeking an increase in the performance of their computers...
memory sub-system to find stable, working memory states at higher FSB frequencies. Memory Divider is also commonly referred as "DRAM:FSB Ratio".
Note that, Memory Dividers are only applicable to those chipsets in which Memory speed is dependent on FSB speeds.
A
Memory divider is a ratio which is used to determine the operating clock
frequencyFrequency is the number of occurrences of a repeating event per unit time. It is also referred to as temporal frequency.The period is the duration of one cycle in a repeating event, so the period is the reciprocal of the frequency....
of
computer memoryComputer memory refers to devices that are used to store data or programs on a temporary or permanent basis for use in an electronic digital computer. Computers represent information in binary code, written as sequences of 0s and 1s...
in accordance with
Front Side BusIn personal computers, the front side bus is the bus that carries data between the CPU and the northbridge.Depending on the processor used, some computers may also have a back-side bus that connects the CPU to the cache...
frequency, if memory system is dependent on FSB clock speed. Along with memory latency timings, memory dividers are extensively used in
overclockingOverclocking is the process of running a computer component at a higher clock rate than it was designed for or was specified by the manufacturer, usually practiced by enthusiasts seeking an increase in the performance of their computers...
memory sub-system to find stable, working memory states at higher FSB frequencies. Memory Divider is also commonly referred as "DRAM:FSB Ratio".
Note that, Memory Dividers are only applicable to those chipsets in which Memory speed is dependent on FSB speeds. Certain chipsets like
nVidiaNvidia is a multinational corporation which specializes in the development of graphics processing units and chipset technologies for workstations, personal computers, and mobile devices...
680i have separate memory and FSB lanes due to which memory clock and FSB clock are asynchronous and memory dividers are not used there. Setting memory speeds and overclocking memory systems in such chipsets are a different issue which do not use memory dividers. This article is only applicable to those chipsets in which memory clock is dependent on FSB clock.
Overview
Memory Dividers allows system memory to run slower than or faster than the actual
FSBIn personal computers, the front side bus is the bus that carries data between the CPU and the northbridge.Depending on the processor used, some computers may also have a back-side bus that connects the CPU to the cache...
(Front Side Bus) speed. Ideally, Front Side Bus and system memory should run at the same clock speed because FSB connects memory system to the CPU. But, it is sometimes desired to run the FSB and system memory at different clock speeds. It is possible to run FSB and memory clock at different clock speeds, within certain limits of the
motherboardA motherboard is the central printed circuit board in many modern computers, and holds many of the crucial components of the system, while providing connectors for other peripherals. The motherboard is sometimes alternatively known as the main board, system board, or, on Apple computers, the logic...
and corresponding
chipsetA chipset or chip set refers to a group of integrated circuits, or chips, that are designed to work together. They are usually marketed as a single product.- Computers :...
. So, settings termed as Memory Divider or FSB/DRAM settings are available and are expressed in a "ratio" which control the difference in memory clock rate and FSB speed.
Entry Level motherboards usually do not provide memory dividers to be changed and the memory dividers are managed by
Memory ControllerThe memory controller is a digital circuit which manages the flow of data going to and from the main memory. It can be a separate chip or integrated into another chip, such as on the die of a microprocessor....
(if chipset supports memory dividers). High end motherboards meant for
overclockingOverclocking is the process of running a computer component at a higher clock rate than it was designed for or was specified by the manufacturer, usually practiced by enthusiasts seeking an increase in the performance of their computers...
provide facilities to change memory dividers (if chipset support memory dividers). However, in certain chipsets memory dividers are not used, because in those systems memory speed is independent of FSB speed.
Description & Application
Usually (Memory Divider) *(
Front Side BusIn personal computers, the front side bus is the bus that carries data between the CPU and the northbridge.Depending on the processor used, some computers may also have a back-side bus that connects the CPU to the cache...
Frequency) gives I/O Bus clock of the memory. Memory clock then determines the final operating frequency or effective clock speed of memory system depending upon DRAM types (DDR, DDR2 and DDR3 SDRAM).
By default, FSB speed and memory are usually set to a 1:1 ratio, meaning that increasing FSB speed (by
overclockingOverclocking is the process of running a computer component at a higher clock rate than it was designed for or was specified by the manufacturer, usually practiced by enthusiasts seeking an increase in the performance of their computers...
) increases memory speed by the same amount. Normally system memory is not built for overclocking and thus may not be able to take the level of overclocking that the processor or motherboard can achieve. The memory divider allows users to mitigate this problem by reducing the speed increase of the memory relative to that of the FSB and the processor.
Example
Suppose a computer system has DDR memory, a Memory Divider of 1:1, a FSB operating at 200 MHz and a CPU multiplier of 10x. Then, the base memory clock will operate at (Memory Divider) *(FSB) = 1*200 = 200 MHz and the effective memory clock would be 400 MHz since it's a DDR system ("DDR" stands for Double Data Rate; the effective memory clock speed is double the actual clock speed). The CPU will operate at 10*200 MHz = 2.0 GHz. Using I/O bus frequency of 200 MHz various types of
DRAMDram or DRAM may refer to:As a unit of measure:* Dram , an imperial unit of mass and volume* Armenian dram, a monetary unit* Dirham, a unit of currency in several Arab nationsOther uses:* Dynamic random access memory...
will operate as:
DDR SDRAMDouble data rate synchronous dynamic random access memory is a class of memory integrated circuits used in computers. It achieves nearly twice the bandwidth of the preceding single data rate SDRAM by double pumping without increasing the clock frequency.With data being transferred 64 bits at...
at 400 MHz (DDR -400 or PC -3200)
DDR2 SDRAMDDR2 SDRAM is a double data rate synchronous dynamic random access memory interface. It supersedes the original DDR SDRAM specification and the two are not compatible...
at 800 MHz (DDR2-800 or PC2-6400)
DDR3 SDRAMIn electronic engineering, DDR3 SDRAM or double-data-rate three synchronous dynamic random access memory is a random access memory interface technology used for high bandwidth storage of the working data of a computer or other digital electronic devices...
at 1600 MHz (DDR3-1600 or PC3-12800)
Now suppose that we overclock FSB to 250 MHz so that CPU operates at 10*250 MHz = 2.5 GHz and memory clock operates at 250 MHz (Memory Divider*FSB). Since DDR-400 RAM is used then effective memory clock (Actual Memory Frequency) will be 500 MHz. A normal DDR-400 SDRAM will fail to work at 500 MHz since it is designed to work at 400 MHz and system will become unstable. But a modern CPU (having overclocking potential) can work at 2.5 GHz (even if it is designed to work at 2 GHz) flawlessly without giving any problem of stability. To keep running overclocked CPU at 2.5 GHz or even at higher speeds (by increasing FSB) we need to slow down memory clock so as to achieve a stable system. For this if we decrease DRAM:FSB ratio to say 4:5 then resulting memory clock speed is (4/5)*250 MHz = 200 MHz resulting effective clock speed of 400 MHz on DDR-400. So, we are able to operate upon a stable overclocked CPU at 2.5 GHz from 2 GHz without increasing effective memory clock.