UPGRADING REPAIRING PCs

Memory Types 41
transfers to and from a 128-bit memory bus instead of the slower
(100MHz or 66MHz), 32-bit or 64-bit data transfers of SDRAM and
previous memory types.
RDRAM modules are called RIMMs (Rambus Inline Memory Module),
and any unused RIMM slots on a motherboard must be filled with
a continuity module to permit a continuous high-speed data pathway
through the RIMMs (see Figure 2.10). Each RIMM represents
multiple memory banks, and thus a single RIMM at a time can be
added to a system—much the way installation of DIMMs works,
although the memory types are not interchangeable.
1.00 [0.039] 3.00 [0.118]
Detail A
4.00 [0.157]
5.675 [0.2234]
REF.
A-1
+
COMPONENT AREA
(A SIDE)
+
B-1
133.35 +0.15
-0.15 5.250+0.006
-0.006
+
Detail B
1.00[0.039]
11.50[0.453]
4.50[1.772]
45.00[1.777]
27.50[1.083]
45.00[1.772]
+0.08
55.18
-0.08
78.17[3.078]
REF.
2.172+0.003
-0.003
-A-
+
+
COMPONENT AREA
(B SIDE)
+
+
+
B-92
17.78 [0.700]
0.85 [0.033]
4.00 +0.15
-0.15 0.157+0.006
-0.006
-B-
A-92
1.27 +0.10
-0.10
0.050 +0.004
-0.004
+0.10
3.00
-0.10
0.80 +0.10
Detail B
-0.10
TYP. 184 PLCS
0.15 +0.10
-0.10
3XScale
2.99 +0.05
-0.05
Capacitor
CSP
Note: Components
Not Always Present
on B side
0.75-1.35
[0.030-0.053]
-C-
+
3XScale
Figure 2.10 Typical RDRAM bus layout, showing two RIMMs and one
continuity module installed.
DDR SDRAM
Double Data Rate (DDR) SDRAM memory is an improved version of
standard SDRAM in which data is transferred twice as fast. Instead
of doubling the actual clock rate, DDR memory achieves the doubling
in performance by transferring twice per transfer cycle—once
at the leading (falling) and once at the trailing (rising) edge of the
cycle. This is similar to the way RDRAM operates and effectively
doubles the transfer rate, even though the same overall clock and
timing signals are used.
DDR SDRAM is supported by many of the newest server chipsets
and provides a design alternative to the more radical RDRAM. The
DDR Consortium—an industry panel consisting of Fujitsu, Ltd.;
Hitachi, Ltd.; Hyundai Electronics Industries Co.; Mitsubishi
Electric Corp.; NEC Corp.; Samsung Electronics Co.; Texas
Instruments, Inc.; and Toshiba Corp.—undertook official standardization
of DDR.
2.00 +0.10
-0.10
3.99 +0.10
-0.10
DDR-SDRAM uses a new DIMM module design with 184 pins.
Figure 2.11 shows the DDR SDRAM DIMM.