will this work in a dell e5520 laptop?

No, this memory upgrade is compatible with Dell Poweredge 1800 servers only.

is this desktop memory or server memory ?

This Memory is intended for Server Only. Not for Desktop

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CMS 8GB (2X4GB) DDR2 3200 400MHZ ECC REGISTERED DIMM Memory Ram Upgrade Compatible with Dell® Poweredge 1800 Ddr2-Pc3200 For Server Only - B47

Computer Memory Solutions guarantees compatibility with models provided in description.
Memory Type: ECC Registered DIMM, 240-Pin
Speed: DDR2-3200, 400 MHz
2 Piece Kit
Product appearance may vary. Picture for reference only. limited lifetime warranty when bought directly from computer memory solutions