There is more than 1 kind of DDR2  FULLY BUFFERED RAM is not compatible with UNBUFFERED RAM or Registered ECC RAM.  The 1420 is a totally DIFFERENT Chipset.

Dell Precision Workstation 490 Memory

Maximum Memory 32GB

Memory Slots 8 Sockets

Chipset: Intel 5000X Chipset

Memory Speed options: PC2-4200 DDR2-533 240pin Fully Buffered SDRAM DIMM

The 1420 uses  Single-Rank PC2-4200 ECC Registered DDR2 DIMM Memory

louieuk,

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Below are the memory specs for the Inspiron 1420 and also the Precision 490.

Inspiron 1420

Memory module connectors Two SODIMM connectors

Memory module capacities 512 MB, 1 GB, and 2 GB

Memory type 667 MHz SoDIMM DDR2

Minimum memory 512 MB (APJ only) 1 GB (all other regions)

Maximum memory 4 GB

Precision 490

Memory

Type

 NOTICE: Full-length heat spreaders (FLHS) are required for 667-MHz DIMMs.

533- and 667-MHz Fully Buffered DDR2 SDRAM (Fully Buffered DIMMs or FBDs)

Memory connectors

8

Memory capacities

512-MB or 1-, 2-, or 4-GB ECC

Minimum memory

1 GB

Maximum memory

32 GB

BIOS address

F0000h

The 1420SC is a power edge Server. Doesn't use Sodimms aka Laptop Memory.

However it does not use FB DIMMS aka Fully Buffered Dimms.