UPDATE 4-Rackable Systems to buy Silicon Graphics for $25 mln

* Silicon Graphics files for Chapter 11, agrees to sale

* Silicon Graphics lists total debt of $526.5 mln

* Transaction expected to close within 60 days

* Silicon Graphics slump 81 pct; Rackable Systems down 11 pct (Adds background, updates to share closing)

By Bijoy Anandoth Koyitty

BANGALORE, April 1 (Reuters) - Server and data storage products maker Rackable Systems Inc RACK.O on Wednesday said it agreed to buy Silicon Graphics Inc SGIC.O, which filed for bankruptcy protection earlier in the day, for about $25 million in cash.

In a filing with the U.S. Securities and Exchange Commission, Silicon Graphics said it expects to pay off secured creditors with net proceeds from the sale.

Shares of Silicon Graphics, which provides servers, storage and related support, plunged as much as 81 percent, while those of Rackable Systems fell about 11 percent.

"While details of the transaction remain unclear, we view the acquisition as a long-term positive for Rackable Systems shares," analyst Doug Reid of Thomas Weisel Partners wrote in a note to clients.