IRIS, the UK's largest privately owned software and services business, has acquired ATW Information Technology Systems. AWT is a reseller and partner of accounting software suite IRIS Exchequer. The Sussex-based firm will join the portfolio of the IRIS Accounting & Business Solutions Division, which comprises the mid-market ERP systems, IRIS Exchequer and IRIS Chorus and the Professional Service Automation solutions, IRIS PROJECTminder and IRIS SharpOWL.