i82845 SDR Chipset

It’s nobody’s secret the Intel Pentium 4 sales have been slow to rise due to high costs partly caused by the RAMBUS memory that remains up to three times more expensive than SDRAM memory. To boost Pentium 4 sales, popularize the platform and wipe out the Pentium III, Intel has recently introduced the Intel i845 chipset codenamed "Brookdale". This chipset has got the specificity to support Pentium 4 processors and PC133 SDRAM memory. Actually there are two flavours of the i845 chipset: the i845 B0 stepping chipset supports DDR memory, as we’ll see below. PC133 SDRAM features a one way channel bandwidth of 1 GB/s against 3.2 GB/s for Rambus memory. This lead to a math problem: indeed the Pentium 4 Quad pumped data bus delivers up to 3.2GB of data per second while the i845 chipset can support only 1GB/s. Due to this limitation the processor will most likely be starved for data resulting in poor performance the SDRAM very low latency time won’t be able to get a boost. With 256 MB of SDRAM actually priced around $30 it’s clear the i845 is a good deal to own an affordable Pentium 4 system.

   The i845 chipset features a similar architecture than previous i81x models: it is composed of the MCH (Memory Controller Hub), and the 82845 (a kind of bridge). The i845 is obviously completed by the well known tried and tested ICH2 component (i82801BA) for total support of the most recent norms that is to say: 2xUDMA 100, AGP 4x with a maximum bandwidth of 1 GB/s, 4 USB 1.1 ports, PC 133 SDRAM (up to 512MB only), AC’ 97 2.1/MC97 and integrated 10/100Mb/s LAN features. Obviously the chipset includes two USB 1.1 controllers for a global bandwidth of 24 MB/s across the four USB ports.

Intel i845 Chipset & Intel Pentium 4 Processor

i82845 B0 Stepping (DDR) Chipset

   The new i845 B0 Stepping (aka i845D) chipset is strictly identical to the native i845. It's exactly the same silicon except that the revision B0 allows the use of DDR-SDRAM memory instead of SDRAM in order to offer better performances. Thus i845D based motherboards offer an appreciable 2GB/sec memory bandwidth that is sufficient for plenty of today’s applications. The i845 B0 stepping is composed of the traditional MCH (Memory Controller Hub), and the 82845 (a kind of bridge): both units are linked by a 266MB/sec interlink bus.

Intel i845 & i845 B0 Chipset Diagrams

   It's quite obvious that the Pentium 4 2.2GHz & DDR PC2100 memory couple isn't in perfect osmosis, since the FSB of the CPU is clocked at 400MHz while the memory turns at 266MHz thus, in some case, the CPU will have to wait for the memory to provide data. Nonetheless it offers good performance for an affordable price. The i845 B0 is obviously completed by the well known tried and tested ICH2 component (i82801BA) for total support of the most recent norms that is to say: 2xUDMA 100, AGP 4x with a maximum bandwidth of 1 GB/s and FastWrites, 4 USB 1.1 ports, PC 2100 DDR-SDRAM (up to 2GB), AC’ 97 2.1/MC97 and integrated 10/100Mb/s LAN features. Obviously the chipset includes two USB 1.1 controllers for a global bandwidth of 24 MB/s across the four USB ports. Note that you can use PC1600 (DDR200) or PC2100 DDR (DDR 266) memory with a i845 B0 based motherboard.