X0305 4 2012-04-01 0 0000873044 RADISYS CORP RSYS 0001282683 Nierenberg Investment Management Company, Inc. 19605 NE 8TH STREET CAMAS WA 98607 1 0 1 0 0001040899 Nierenberg David 19605 NE 8TH STREET CAMAS WA 98607 0 0 1 0 0001282685 D3 Family Fund, LP 19605 NE 8TH STREET CAMAS WA 98607 0 0 1 0 0001365745 D3 Family Bulldog Fund, LP 19605 NE 8TH STREET CAMAS WA 98607 0 0 1 0 0001405824 D3 Family Canadian Fund, LP 19605 NE 8TH STREET CAMAS WA 98607 0 0 1 0 Common Stock 2012-04-01 4 M 0 243 A 727753 I By The D3 Family Fund, LP Common Stock 2012-04-01 4 M 0 977 A 2743659 I By The D3 Family Bulldog Fund, LP Common Stock 2012-04-01 4 M 0 113 A 256208 I By the D3 Family Canadian Fund, LP Common Stock 801176 I By The DIII Offshore Fund, LP Restricted Stock Unit 2012-04-01 4 M 0 243 D Common Stock 243 1857 I By the D3 Family Fund, LP Restricted Stock Unit 2012-04-01 4 M 0 977 D Common Stock 977 7443 I By the D3 Family Bulldog Fund, LP Restricted Stock Unit 2012-04-01 4 M 0 113 D Common Stock 113 867 I By the D3 Family Canadian Fund, LP Each of the reporting persons disclaims beneficial ownership of these securities except to the extent of the reporting person's pecuniary interest therein. David Nierenberg is a member of to the Board of Directors of the issuer. As a director, Mr. Nierenberg was granted 4,000 restricted stock units on April 1, 2011, which vest 33% per year on the anniversary of the grant date. These restricted stock units are held for the benefit of the reporting persons identified above in Table II of this Form 4. Each restricted stock unit represents a contingent right to receive one share of the issuer's common stock. One share of common stock will be automatically delivered to the reporting person for each restricted stock unit that vests. On April 1, 2012, 33% of the Restricted Stock Units granted on April 1, 2011 vested and were delivered to the reporting persons as described in Table I of this Form 4. David Nierenberg 2012-04-03 David Nierenberg, President, Nierenberg Investment Management Company, Inc. (NIMCO) 2012-04-03 David Nierenberg, President, NIMCO, General Partner of The D3 Family Canadian Fund, LP 2012-04-03 David Nierenberg, President, NIMCO, General Partner of The D3 Family Bulldog Fund, LP 2012-04-03 David Nierenberg, President, NIMCO, General Partner of The D3 Family Fund, LP 2012-04-03