Memory Matters: Why It Should Be DDR
RDRAM in the current PC800 standard will be replaced soon, as the performance benefits in contrast to DDR memory are gone. DDR-based chipsets like the VIA P4X266A, the SiS645 (this one even at 166 MHz memory clock) or the i845 offer similar or equal performance at reduced costs with respect to both the chipset and the memory.
In a few months, Intel will be offering the Pentium 4 for 533 MHz FSB . Simultaneously, a new RDRAM standard will appear (PC1066 at 533 MHz double-pumped), working perfectly synchronously with the clock speed. The first benchmarks proved that the team consisting of RDRAM + Pentium 4 makes much more sense than most of us imagined, and that common systems with DDR memory lag a bit behind. In this context, I would like to underline that we are talking of a price segment that is clearly higher than the one represented by these 19 motherboards. Both the new CPUs (2.4+ GHz) as well as the chipset and the memory will be available at lunatic prices. Only fat wallets, please.
So get ready for DDR as the old and new alternative! Though dual-channel PC1066 RDRAM will be quite a bit ahead of DDR memory, the latter will finally also work synchronously with the FSB. But DDR clock speeds could also be soon increased, bringing systems with 166 (DDR333) or even 200 MHz (DDR400) memory clock (double-pumped, of course).
| Header Cell - Column 0 | RDRAM | DDR-SDRAM |
|---|---|---|
| Clock | 400 MHz (double-pumped) | 133 MHz (double-pumped) |
| Name of module | Rambus Inline Memory Module (RIMM) | Dual Inline Memory Module (DIMM) |
| Interface | 16 Bit | 64 Bit |
| Access | via a dedicated protocol | via classic memory grid |
| Bandwith | 2 Byte (16 Bit) x 800 MHz= 1600 MB/s | 8 Byte (64 Bit) x 266 MHz= 2133 MB/s |
| Bandwidth in real life | 3.2 GB/sDual-Channel PC800 RDRAM | 2.1 GB/sPC2100 DDR-SDRAM |
| ECC available? | yes | yes |
| Largest module available | 512 MB | 1 GB |
| Usage | Two RIMMs only. Empty slots have to be equipped with continuity RIMMs. | single |
| Performance Differences | Yes, 35 and 40 ns | yes, due to several memory parameters (e.g. CAS Latency) |
| Memory manufacturing costs | medium | low |
| Motherboards manufacturing costs | medium to low | medium to low |
| Platforms | Intel Pentium III, Pentium 4 | Intel Celeron, Pentium 4, Pentium IIIAMD Duron, Athlon, Athlon XP, Athlon MPVIA C3 |
From the table above, you can tell that there are several advantages of DDR memory:
- Better upgradeability: single DIMMs can be added
- Availability on all platforms: when changing to an Athlon XP system, you can continue using your DDR memory
- Larger modules allow larger maximum memory sizes
