Compaq Deskpro EP 6233 Technical Reference Manual page 48

Chapter 3 Processor/Memory Subsystem
3.3.2 SYSTEM MEMORY
The 100-MHz slot 1system board contains three 168-pin DIMM sockets for system memory. This
system is designed for using SDRAM DIMMs. As shipped from the factory the standard
configuration has 64 megabytes of SDRAM installed. The system memory is expandable up to a
maximum of 384 megabytes. Single or double-sided DIMMs may be used. In expanding the
standard memory using modules from third party suppliers the following DIMM type is
recommended: 66- (9.0 ns) or 100-MHz (6.0 ns) unbuffered SDRAM supporting CAS
latency (CL) 2 or 3.
NOTE: The DIMM speed should match the host bus speed of the processor (i.e., use 66-
MHz DIMMs in a system with a 266/66 processor and 100-MHz DIMMs in a system
with a 350/100 processor).
In addition to the supplied (and recommended) SDRAM, the system supports ECC RAM. The
RAM type and operating parameters are detected during POST by the system BIOS using the
serial presence detect (SPD) method. This method employs an I
EEPROM on each installed DIMM. The EEPROM holds the type and operating parameter data.
The supported format 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 is
shown in Table 3-3.
The key SPD bytes that BIOS checks for compatibility are 2, 9, 10, 18, 23, and 24. If BIOS
detects a mix of SDRAM and EDO DIMMs only the SDRAM DIMMs will be enabled. If ECC
DIMMs are used, all DIMMs installed must be ECC for ECC benefits (error logging) to be
realized.
Once BIOS determines the DIMM type the DRAM speed and CAS latency is checked based on
the following criteria:
Only CAS latencies of 2 or 3 are supported. If DIMMs with unequal CAS latencies are installed
then operation will occur based on the DIMM with the greatest latency.
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.
The system memory map is shown in Figure 3-4.
3-12 Compaq Deskpro EP Series of Personal Computers
Bus Speed Cycle Time
66 MHz 15 ns
100 MHz 10 ns
First Edition - April 1998
2
C bus to communicate with an
Access
from
Clock
9 ns
6 ns