IBM Links

http://www-1.ibm.com/servers/eserver/support/zseries/index.html
zSeries and S/390 Technical Support. From here you can access technical data, fixes, and publications.
http://publibz.boulder.ibm.com/cgi-bin/
bookmgr_OS390/BOOKS/IEA1B604/CCONTENTS?DT=19970715180443
IBM's JCL manual online
http://www-1.ibm.com/servers/eserver/zseries/zos/bkserv/
IBM z/OS Internet Library
http://www.redbooks.ibm.com/
The IBM Redbooks home page. Redbooks are additional books written by various experienced IBM system programmers (not necessarily from IBM), and they tend to be more 'how to' oriented, including specific examples of things like VTAM and IOCP definitions.

General Mainframe Links

http://www.aceshardware.com/read.jsp?id=50000316
A general overview of IBM mainframes
http://www.okstate.edu/cis_info/cis_manual/jcl_toc.html
Job Control Language (JCL) Introduction
http://www.geocities.com/~oberoi/mainfrme.html
A page full of links to mainframe-related information.
http://www.InstantWeb.com/l/loriaux/s390/
Loriaux's System/390 home page. A "Mainframers meeting point."

WAN Protocol Links

http://www.dcbnet.com/notes/9611t1.html
All You Wanted to Know About T1 Connections, But Were Afraid to Ask
http://www.dcbnet.com/notes/framerly.html
Frame Relay overview
http://www.nationalisdncouncil.com/index.html
National ISDN Council
http://www.cisco.com/univercd/cc/td/doc/cisintwk/ito_doc/ibmsnaro.htm
Overview of routing SNA by Cisco

TCP/IP Protocol Links

http://www.garykessler.net/library/tcpip.html
An extremely valuable overview of TCP/IP and the Internet
http://www.iana.org/assignments/port-numbers
A list of well known TCP and UDP port numbers
http://www.ietf.org/rfc/rfc1179.txt
The RFC (Request for Comments) regarding the Line Printer Daemon Protocol (LPD)
http://www.ietf.org/rfc/rfc959.txt
The RFC (Request for Comments) regarding the File Transfer Protocol (FTP)
http://www.ietf.org/rfc/rfc1795.txt
The RFC (Request for Comments) regarding Data Link Switching (DLSw)

SNA Protocol Links

http://www.yale.edu/pclt/COMM/SNA.HTM
Introduction to SNA
http://www.cisco.com/en/US/tech/tk331/tk341/tech_brief09186a00800b4258.html
Cisco technology Brief on SNA

DOS TCP/IP Software Links

http://supportweb.netmanage.com/
FTP Software (now NetManage) Help Desk and Knowledge Base
http://supportweb.netmanage.com/ts_viewnow/downloads/param.asp
FTP Software's (now NetManage) PC/TCP Kernel Software "Configuration Parameter Reference" document

Printer Links

http://www.i18nguy.com/unicode/codepages.html
Documentation on all popular code pages, including various ASCII and international code pages.
http://h20000.www2.hp.com/bizsupport/TechSupport/Document.jsp?objectID=bpl02705
Lists the HP LaserJet PCL printer commands for basic page formatting and font selection..
http://www.xerox-techsupport.com/
Information, FAQs, and PDFs dealing with Xerox enterprise production printers, including all LPS, NPS, IPS, and EPS models. Also contains information on XPAF.
http://www.xerox-techsupport.com/cgi-bin/Ultimate.cgi
Xerox production printer user forums
http://www.unicode.org/
Unicode Home Page. Contains information and documentation on Unicode.
http://www.unicode.org/unibook/
The Unibook Character Browser is a freeware code page encyclopedia that allows you to look up all of the Unicode characters and their respective graphic symbols. It is handy for troubleshooting code page issues.

Windows NT/ 2000 Links

http://www.ntfaq.com
http://www.ntfaq.com
http://www.microsoft.com/technet/
Microsoft Technet
http://support.microsoft.com/default.aspx?scid=KB;en-us;q216206
Blue Screen or STOP Error Message Troubleshooting
http://www.microsoft.com/technet/treeview/default.asp?url=/TechNet/prodtechnol/winntas/tips/techrep/bsod.asp
Demystifying the "Blue Screen of Death"

SNA Server / Host Integration Server Links

http://www.kbalertz.com/technology.aspx?tec=189
Links to all Microsoft knowledge base articles on SNA Server
http://www.kbalertz.com/technology.aspx?tec=73
Links to all Microsoft knowledge base articles on Host Integration Server