MAXIMUMPC MARCH 2004
as double-sided DIMMs) let you install
more memory into a single slot and, in
recent tests with high-speed overclock-
friendly memory, improve performance
over single-bank modules.
In rare cases, you may find moth-
erboards with three memory sockets
that use chipsets that support just four
banks of memory. Thus, if two dual-
bank/double-sided modules are already
installed, you must leave the third socket
empty. Some systems support dual-bank
modules in slots 1 and 2, but slot 3 can
use only single-bank memory.
Older systems designed for use with
DDR266 (PC2100) memory might be less
stable if you use nonstandard memory
timings, but systems designed for DDR333
(PC2700) and faster memory usually work
well with either standard or nonstandard
memory timings, regardless of whether
the modules are single-bank or dual-bank.Current memory
technologies
The oldest type of memory in wide-
spread use is PC133 (133MHz) SDRAM
(synchronous DRAM). SDRAM performs
one operation per clock cycle. (See RAM
stats on page 55 for details.)Generally, memory manufactur-
ers are very conservative in their
memory timings, so it pays to try
tweaking your RAM settings, even
if you don’t overclock your sys-
tem. In a series of experiments,
we determined that the following
adjustments gained us about 3
percent faster memory perfor-
mance according to SiSoft Sandra :
lowering the memory’s default CAS
latency from 2.5 to 2, lowering the
RAS to CAS Delay from 3 to 2, low-
ering the RAS Precharge from 3 to
2, lowering the Active to Precharge
from 6 to 5, and lowering the com-
mand rate from 2T to 1T. Your mile-
age, of course, may vary.
Given identical memory mod-
ules, the chipset used by a given
motherboard is often the most
important factor in determining
how fast the memory subsystem
is. Many motherboard and sys-
tem reviews look closely at both
the memory and the chipset. You
should too.How to Improve
Memory Performance
by Adjusting Memory
Timing
Memory Parameter Common
AbbreviationWhat It Does Range of Typical Values
(in clock cycles)
RAS to CAS Delay tRCD Activates row 2 or 3
CAS Latency CAS, CL Delay between activation of
row and reading of row2, 2.5, 3 (DDR)
2, 3 (SDRAM)
RAS Precharge tRP Deactivates row 2, 3
Command Rate Delay between chip select
and command1, 2Active to Precharge
DelaytRAS Number of clock cycles
between activation and
deactivation of row3, 4, 5, 6, 7Table 1 This table shows the most
common memory parameters that can
be tweaked in the ")/S, how they are
often abbreviated in ")/S screens, what
they affect, and the typical values they
can be assigned.RAM:
All Questions Answered!
&igure /nce you’ve disabled S0D, you’re free to experiment with different
settingsthat is, as long as you’ve got a motherboard that permits it.