Ram Type

Posted on 2000-03-19
Last Modified: 2012-05-04
What is the difference btween EDO Ram and Fast Page Mode ? Can they be used together
in the same machine ? I have a PowerTower Pro 225 and A PowerCenter Pro 210. The Tower machine supports interleaving. I want to take some of the Ram out of the 210
and install in the Tower so as to interleave the ram. Can I do this ?
Question by:choc9
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Accepted Solution

weed earned 50 total points
ID: 2633647
The short answer, yes. You should have no problems moving ram from the power center pro 210 to the PowerTower. They use the same type of ram. 168 pin DIMMs for those machines were all the same.

Now for the long answer...which is actually totally irrelevant to moving memory between the two machines....The difference between EDO and FPM...This was cut and paste so pardon the tech speak.

Extended Data-Output (EDO) is a DRAM technology that improves the performance of the memory subsystem while maintaining backward compatibility with previous systems.

In basic terms, EDO can be viewed simply as a very fast standard DRAM. In technical terms, the essential advantage of EDO is shorter Page Mode cycle times than standard Fast Page Mode (FPM) DRAM. In FPM DRAMs, the output buffer is turned off with the rising edge of CAS (column address strobe) and the output data is no longer available. In EDO memory, this is not the case-the data is not turned off by the rising edge of CAS. This effectively means that the data is available for a longer period, thereby enabling the system to read output data while setting up for the next cycle. In achieving this, EDO saves one clock cycle for every page access, resulting in a significant increase in system performance.

In addition to this fundamental difference in operation, EDO has two other key features. The memory design offers both increased peak memory bandwidth and simplified constraints on access timing, which help to increase memory performance. As an example of the performance increase, while a 60ns standard FPM DRAM offers a 40ns cycle time, a 60ns EDO DRAM offers a 25ns cycle time. EDO typically results in a 10-15% overall performance increase in systems that are designed to take advantage of this technology.

Where is EDO appropriate?
While the logical application of this fast DRAM is to squeeze every bit of performance out of systems with the very latest processors, there is also an important place for it with the low-end of Pentium systems. Because these technologies narrow the gap between DRAM and SRAM performance, the use of it with a high speed processor will enable system vendors to offer cacheless systems that still deliver high-speed capability. Since the incremental cost of EDO is virtually zero, vendors will be able to move to lower price points without giving up much performance. This approach is particularly attractive for notebook systems. Gaining performance without having to incorporate external L2 cache lowers power consumption (lengthens battery life), lowers heat dissipation needs, and minimizes board real estate demands.

What does this mean for the installed base and future memory purchases?
Fortunately, since EDO memory acts very similarly to conventional FPM DRAM, the impact of the growth of this technology is minimal. EDO uses the same signals and packages as FPM DRAM. In most cases, EDO will work in systems that were designed to work only with FPM. This even includes Apple Macintosh systems that use industry standard 32-bit, 72-pin SIMMs. As would be expected, the increase in performance typically associated with EDO would not occur. Most new chipset designs will allow any combination of both technologies (FPM and EDO) to be used. Placing standard DRAM modules in a system equipped to utilize EDO will also not cause problems. The system will function properly, just without the performance boost the faster memory could have provided. If you mix EDO and non-EDO modules in a system, function will be unaffected and performance will be at standard FPM DRAM levels. It is recommended that modules using different types of DRAM not be mixed within a memory bank.

EDO modules are available in the same configurations as FPM modules and use the same board design. Because the only differences between Fast Page Mode and EDO are within the DRAM chip, it is difficult to distinguish between these two modules by sight. The only visible difference will be the DRAM part numbers.
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Expert Comment

ID: 2633652
I just found a slightly simpler definition which may also be insightful. And yes, they will work together in the same machine.

Fast Page Mode (FPM) is an older technology category of DRAMs. FPM DRAMs have the ability to work within a page. A page is described as the section of memory available within a row address. Within one specific row are several columns of memory bits. With FPM DRAMs, the row address only needs to be specified once for accesses within the same page addresses. Successive accesses to the same page of memory only require the selection of a column address, which saves time in accessing the memory. JEDEC, the electronic standards agency, has specified standards for the FPM DRAM.

Extended Data Output (EDO) was a subsequent DRAM chip technology in a line of innovations which included Nibble Mode, Write Per Bit, and Fast Page Mode. EDO is one step better than Fast Page Mode; for a given speed of chip (i.e. 70ns, 60ns) EDO chips allow the CPU to access memory 10 to 15% faster. A computer system must be designed to utilize the extra efficiency EDO offers. Pentium-class computers using Intel's Triton chip set are designed to use EDO memory. EDO memory will function in a machine that does not recognize EDO, however no performance benefit will be realized.

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