With about four weeks to go before the US presidential election, states across the US are preparing for heavy voter turnout that could cause problems for local elections officials and electronic voting systems.

To address those challenges, election officials say they're ramping up early to review Election Day preparations and ensure that there are enough paper ballots on hand and that poll workers are adequately trained.

To gauge that progress, Computerworld checked with several US states where e-voting problems have occurred since 2000 to see what changes have been made and how all is expected to proceed on November 4.

Critics have long argued that the controversial touch-screen electronic machines, where voters simply touch ballot selections on a screen to choose their candidates, are unreliable and provide no means for a paper trail to manually recount each vote in the event of a problem.

In response to such criticisms, many of those touch-screen machines, also called direct recording electronic (DRE) machines, were modified so that voters received a printout to confirm their choices when casting their ballots.

Other states have made even bigger system changes since the 2004 presidential election, moving away from DREs and replacing them in large part with paper ballot systems that use optical scanners to tally the votes.

Yet no system has proved flawless, as evidenced by August's primary election woes in Florida, where optically scanned paper ballots were used to replace what had been touch-screen-only e-voting machines.

While Florida election officials believe that the optical-scanning equipment worked properly, the large number of paper ballots -- 102,523 were cast in the primary -- caused trouble for officials who had to conduct a recount due to a judicial race that was separated by only 17 votes. The closeness of the race triggered a mandatory recount that remains unresolved because of problems in organizing and recounting the ballots.

Overall, the US has a mosaic of different kinds of voting systems that vary among states, counties and even precincts. Some voting districts use only one type of voting system, such as optically scanned paper ballots or touch screens with or without paper receipts, while many others use combinations of systems.

E-voting watchdog group Verified Voting provides a state-by-state and locality-by-locality interactive graphic that details the election systems used across the nation. Users can see the types of equipment used, as well as details on systems used by neighboring municipalities.