Table of Contents
Advertisement
that allow configurable combinations of controller data bus widths. These modes
allow its bandwidth and capacity to be optimized for many system configurations.
1.6.5 Ranks
A
rank
is a set of DRAM chips on a DIMM that provides eight bytes (64 bits) of
data.
Memory in servers is implemented in the form of DIMMs, which contain a number
of SDRAM (or just DRAM) chips.
The capacity of each DRAM is a number of
(x4), 8 bits (x8) and, starting to become prevalent, 16 bits in length (x16).
The word length is usually written as x4 for 4 bits, and so on. The number of
words in the DRAM is sometimes written on the label of the DIMM, such as a
DRAM chip on a DIMM.
DIMMs are typically configured as either single-rank or double-rank devices but
four-rank devices are becoming more prevalent.
The DRAM devices that make up a rank are often, but not always, mounted on
one side of the DIMM, so a single-rank DIMMs can also be referred to as a
single-sided DIMM. Likewise a double-ranked DIMM can be referred to as a
double-sided DIMM.
Refer to "Chapter 8, Memory subsystem" of the IBM Redbooks publication
Tuning IBM System x Servers for Performance, SG24-5287 for more details.
1.6.6 Comparing IBM eX4 to X3 technologies
This section discusses the improvements in the design of IBM eX4 technology as
compared to the design of previous X3 technology. A block diagram of the X3
technology is shown in Figure 1-13 on page 32.
words
where each word can be 4 bits
Chapter 1. Technical overview
31
Advertisement
Table of Contents
