Number of chips per module

Number of chips per module

Some SIMM's have more chips on the module than others. Looking at just the 32-bit modules,
we find modules with 2, 4, 8 or chips on each side. SIMM's with 2 MB, 8 MB and 32 MB are
double sided. There are chips on both sides of the module. All these chips 16 Mbit ones.

The newest DIMM-modules holds 64 Mbit RAM chips. This way a 32 MB module is made of
only 4 chips since 4 X 64 / 8 = 32.

Pentium system board with SIMM's

On the Pentium system board, the system bus is 64 bit wide. Therefore, the SIMM's are
installed in pairs. Since the standard system board only has two banks with a total of four SIMM sockets, RAM expansion possibilities are limited. NOTE: never use different speed RAM
modules on the Pentium system board. All modules must have the same speed. Here you see
a few configurations on a Pentium system board with four SIMM sockets:

Certain system boards (like TYAN) have 6 or 8 SIMM sockets. That provides more RAM
expansion flexibility.


The latest RAM type, SDRAM are made in 64 bit wide modules called DIMM's. They have a
168 pin edge connector. They fit only in the newer system boards. The 82430 VX and TX chip
sets can control SDRAM, as well as the LX and BX chip sets do.

Since the DIMM modules are 64 bits wide, you can install one module at a time. They are
available in 8, 16, 32, 64, 128 and 256 MB, with 8, 10, and 12 ns speed. There are usually
three DIMM sockets on a system board.

The advantage of SDRAM is increased speed. That allows you to increase system bus speed.
With 60 ns EDO-RAM, you can run at a maximum of 75 MHZ on the system bus, while SDRAM speed can increase to at least 100 MHZ.
Some system boards have both SIMM and DIMM sockets. The idea is that you can choose
between re use EDO RAM in the SIMM sockets, or install SDRAM in the DIMM sockets. They are not designed to mix RAM types although it works at some boards.

Above: a 64 MB DIMM-module holding 32 chips each of 16 Mbit (32 X 16 Mbit / 8 bit = 64 MB).
It is better to use DIMM's made of the the new 64 Mbit chips. A 64 MB module is this way made of only 8 chips (8 X 64 Mbit / 8 bit = 64 MB).


The newest DIMM-modules include a EPROM-chip holding information about the module. This chip works as a SPD (Serial Presence Detect) - a unit storing information about the RAM type. The idea is that BIOS can read these information and this way tune the system bus and the timings for a perfect CPU-RAM performance.

With BX chip set the system bus speed has come up to 100 MHZ. This puts new focus on the
quality of the RAM modules. Hence Intel has made a new standard called PC100. Only
SD-RAM modules that are constructed according to these standards are guaranteed to work at
100 MHZ. In some articles this new RAM is described at 125 MHZ SD-RAM.

Rambus RDRAM

Intel plans to use the so-called Rambus RAM (RDRAM or nDRAM) in the future. It is a
advanced technology from an American company, who sells the technology to other chip
manufactories for just 2% in license... And since Intel supports the RDRAM, they are going to
be rich. But RDRAM should be cheap to produce, so we all profit.
Data is read in packets at a very high clock speed. 600 MHZ works fine, and GigaHertz will
follow. We can drop the L2-cache if it works. The RDRAM chips have to be placed very close to the CPU to reduce radio noise.