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Technical Reference Guide
3.3 MEMORY SUBSYSTEM
These systems support one of two types of memory: single data rate (SDR) SDRAM or double
data rate (DDR) SDRAM. The system board determines the type of memory supported:
♦ SDR SDRAM-based system board: Three 168-pin DIMM sockets that accept PC100 or
PC133 (PC133 supplied) DIMMs.
♦ DDR SDRAM-based system board: Two 184-pin DIMM sockets that accept PC1600 or
PC2100 (PC2100 supplied) DIMMs.
NOTE: The two memory types are not interchangeable within a system. The system
board determines memory type.
NOTE: The SDR SDRAM "PCxxx" reference designates bus speed (i.e, a PC133
DIMM is designed for 133 MHz operation). The DDR SDRAM "PCxxxx" reference
designates bus bandwidth (i.e., a PC2100 DIMM can, operating at a 266-MHz effective
speed, provide a throughput of 2100 MBps (8 bytes × 266 MHz)).
These systems accept DIMMs with the following parameters:
♦ Unbuffered, compatible with SPD rev. 1.0
♦ 32-, 64-, 128-, 256-, and 512-Mb memory technology
♦ Single or double-sided
NOTE: Systems that support DDR SDRAM accept either ECC or non-ECC DIMMs,
but not both.
The SPD format supported by these systems complies with the JEDEC specification for 128-byte
EEPROMs. This system also provides support for 256-byte EEPROMs to include additional
Compaq-added features such as part number and serial number. The SPD format as supported in
this system (SPD rev. 1) is shown in Table 3-3.
The key SPD bytes that BIOS checks for compatibility are 2, 9, 10, 18, 23, 24, and 126. If BIOS
detects EDO or ECC DIMMs a “memory incompatible” message will be displayed and the
system will halt. This system is designed for using non-ECC DIMMs only. Refer to chapter 8
for a description of the BIOS procedure of interrogating DIMMs.
An installed mix of DIMM types (PC100 and PC133, CL 2 and CL 3) is acceptable but operation
will be constrained to the level of the DIMM with the lowest performance specification.
If an incompatible DIMM is detected the NUM LOCK will blink for a short period of time during
POST and an error message may or may not be displayed before the system hangs.
Compaq Evo and Workstation Personal Computer
Featuring the Intel Pentium 4 Processor
Second Edition - January 2003
3-5