Hardware Reference
In-Depth Information
Figure 6.4. SDR versus DDR cycling.
To actually use EDO memory, your motherboard chipset had to support it. Most motherboard chipsets
introduced on the market from 1995 (Intel 430FX) through 1997 (Intel 430TX) offered support for
EDO, making EDO the most popular form of memory in PCs from 1995 through 1998. Because EDO
memory chips cost the same to manufacture as standard chips, combined with Intel's support of EDO
in motherboard chipsets, the PC market jumped on the EDO bandwagon full force.
Generation (P6 Pentium Pro/II/III Class) Chipsets
,”
p.
192
.
EDO RAM was used in systems with CPU bus speeds of up to 66MHz, which fit perfectly with the
PC market up through 1998. However, starting in 1998, with the advent of 100MHz and faster system
bus speeds, the market for EDO rapidly declined, and faster SDRAM architecture became the
standard.
One variation of EDO that never caught on was called
burst EDO
(BEDO). BEDO added burst
capabilities for even speedier data transfers than standard EDO. Unfortunately, the technology was
owned by Micron and not a free industry standard, so only one chipset (Intel 440FX Natoma) ever
supported it. BEDO was quickly overshadowed by industry-standard SDRAM, which came into
favor among PC system chipset and system designers over proprietary designs. As such, BEDO never
really saw the light of production, and to my knowledge no systems ever used it.
SDRAM
SDRAM is short for synchronous DRAM, a JEDEC standard for a type of DRAM that runs in
synchronization with the memory bus. SDRAM delivers information in very high-speed bursts using a
high-speed clocked interface. SDRAM removes most of the latency involved in asynchronous DRAM
because the signals are already in synchronization with the motherboard clock.
As with any newly introduced type of memory on the market, motherboard chipset support is required
before it can be usable in systems. Starting in 1996 with the 430VX and 430TX, most of Intel's
chipsets began to support industry-standard SDRAM, and in 1998 the introduction of the 440BX
chipset caused SDRAM to eclipse EDO as the most popular type on the market.
