System Memory - Compaq Deskpro EP 6233 Technical Reference Manual

3.2.4

SYSTEM MEMORY

The 66-MHz slot 1 system board contains two 168-pin DIMM sockets for system memory. This
system provides optimum performance with SDRAM DIMMs. As shipped from the factory the
standard configuration has 32 megabytes of SDRAM installed and is expandable up to a
maximum of 256 megabytes. Single and/or double-sided DIMMs may be used. Different DRAM
technologies (16-Mb, 64-Mb) and different widths (x8, x16, x32) may be mixed . In expanding
the standard memory using modules from third party suppliers the following DIMM type is
recommended: 66-MHz unbuffered SDRAM supporting CAS latency (CL) 2 or 3 with a
data access time (clock-to-data out) of 9.0 ns or less @ CL=2 or CL=3.
In addition to the supplied (and recommended) SDRAM, the system supports EDO and FPM
RAM. The 443EX north bridge does not support ECC memory. 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
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. The
4430EX north bridge does not recognize ECC DIMMs.
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 message may or may not be displayed before the system hangs.
2
C bus to communicate with an EEPROM on each installed
Bus Speed Cycle Time
66 MHz 15 ns
Compaq Deskpro EP Series of Personal Computers
First Edition - April 1998
Technical Reference Guide
Access
from
Clock
9 ns
3-5