I apologise to RChat for some duplication of links from earlier in this thread, but I am hope these two links will remain far more useful for far longer than the new search engine. 
Searching NSW BDM index for Marriages
http://www.bdm.nsw.gov.au/cgi-bin/Index/IndexingOrder.cgi/search?event=marriages  Searching NSW BDM index for Births, Deaths 
http://www.bdm.nsw.gov.au/cgi-bin/Index/IndexingOrder.cgi/search?SessionID=46262022&event=births Early Church Codes
http://www.bdm.nsw.gov.au/bdm_fh/bdm_crh.html Some further info (In general terms, the NSW State Records Office .... formerly the Archives Office, has the physical care of the originals)
NSW SRO 
http://www.records.nsw.gov.au/state-archives/guides-and-finding-aids/short-guide-2/short-guide-2 http://www.records.nsw.gov.au/state-archives/guides-and-finding-aids/short-guide-2/baptisms/baptisms http://www.records.nsw.gov.au/state-archives/guides-and-finding-aids/short-guide-2/marriages/marriages http://www.records.nsw.gov.au/state-archives/guides-and-finding-aids/short-guide-2/deaths/deathshttp://www.records.nsw.gov.au/state-archives/guides-and-finding-aids/short-guide-4/short-guide-4 http://www.records.nsw.gov.au/state-archives/guides-and-finding-aids/short-guide-4/short-guide-4#pre-1856-registers-and http://www.records.nsw.gov.au/state-archives/guides-and-finding-aids/short-guide-4/short-guide-4#listing-of-registers-by http://www.records.nsw.gov.au/state-archives/guides-and-finding-aids/short-guide-4/short-guide-4#arrangement-of-registersVolumes 1 to 123
http://www.records.nsw.gov.au/state-archives/guides-and-finding-aids/short-guide-4/volumes-1-123-1/volumes-1-123   (Bap = Baptism, Bur = Burial, Mar = Marriage)  Notice that each volume starts at its own LINE 1, so there’s many “1/18xx” and many “2/18xx” and many “n/18xx” where n is a real number an xx is any year in the 19th Century where the record is from the NSW BDM Early Church Records collection. 
HISTORICAL BACKGROUND OF EARLY RECORDS…. 
http://www.records.nsw.gov.au/state-archives/guides-and-finding-aids/short-guide-4/short-guide-4#historical-background-of-early http://investigator.records.nsw.gov.au/Entity.aspx?Path=\Activity\37 Birth, Death and Marriage Registration Start 3 Dec 1855 
http://investigator.records.nsw.gov.au/Entity.aspx?Path=\Series\4558 Norfolk Island list of bdm 1870 – 1871
http://investigator.records.nsw.gov.au/Entity.aspx?Path=\Series\12937 1787 - 1951 Registers of Baptisms, Burials, Marriages 
Vols. 1- 44: Church of England 
Vols. 45- 72: Baptisms - All other denominations 
Vols. 73-101: Marriages - All other denominations 
Vols.102-120: Burials - All other denominations 
Vols.121-123: Supplementary Registers - Baptisms, Burials and Marriages, 1827-1901 
http://investigator.records.nsw.gov.au/Entity.aspx?Path=\Series\12944  March 1856 – Aug 1925 Births in  17 volumes
http://investigator.records.nsw.gov.au/Entity.aspx?Path=\Series\12945  Aug 1856 – 1927  births in 4 volumes 
http://investigator.records.nsw.gov.au/Entity.aspx?Path=\Agency\18   “In 1996 the agency listed its prime function as the registration of " births,deaths  and marriages, changes of name, adoptions and legitimation occurring in NSW. It undertakes the maintenance and safekeeping of the records relating to this function, and offers the following services: the issue of certificates relating to births, deaths andmarriages, the collection and provision of selected statistical data to approved organisations and government agencies, the performance of civil marriage ceremonies and administration of matters related to the Commonwealth Marriage Act of 1961”
Cheers,