Extended data output

Extended Data Output (EDO) memory is about 10 to 15 percent faster than FPM memory and is usually found on 66 MHz motherboards. With EDO memory, the memory controller can read data from a memory block while listening for the next instruction. This capability increases performance because the memory controller doesn't have to wait for the next instruction after reading a block of memory; while it is reading one block of memory, it is receiving the next instruction. In contrast, with FPM DRAM, reading one memory block and listening for the next instruction are done in multiple steps.

Burst Extended Data Output

Burst Extended Data Output (BEDO) is a bursting-type technology. The word burst refers to the fact that when one memory address is requested and that address is retrieved, the system bursts into the next couple of blocks and reads those as well. The theory behind BEDO is that the system has already gone through the trouble of locating that block, and chances are that the next request will be for the next block, so why not take that information while the memory controller is already there? If that extra block is the next requested block from the CPU, the memory controller already has the data and can pass it to the CPU immediately.

BEDO is 50 percent faster than EDO. Because of lack of support from computer manufacturers, however, BEDO has not been used in many systems. It has been surpassed by SDRAM instead.

Synchronous DRAM

Synchronous DRAM (SDRAM) is memory synchronized to the system board speed. This synchronized speed means that the data stored in memory is refreshed at the system speed, and data is accessed in memory at the system speed as well.

SDRAM is one of the most popular types of DRAM found in later Pentium systems, such as the Pentium II. When you upgrade memory on your system, if you determine that you need SDRAM, you will then need to determine what speed SDRAM. Because you are running at the system speed, you must match the DRAM speed with the motherboard speed. Thus, if you have a 100 MHz motherboard, you need 100 MHz SDRAM. If you have a 133 MHz motherboard, you need 133 MHz SDRAM.

As mentioned, if you have a 100 MHz motherboard, you will purchase 100 MHz memory, typically labeled PC100. Be aware, however, that there is some flexibility when purchasing SDRAM. For example, I have a 100 MHz motherboard on an old Pentium II system. When I upgraded the DRAM on this system, I couldn't buy PC100 memory because PC133 (which is SDRAM that runs at 133 MHz) was the popular memory at that time. Not a problem! You can use faster memory than your motherboard speed as long as you are willing to accept that you have paid for memory that will not run to its full potential speed. In my example, the 133 MHz memory is only running at 100 MHz due to the speed of the motherboard.