TOKYO - Tokyo Stock Exchange Inc. was forced to halt trading 20 minutes earlier than usual last Wednesday when its computer system nearly reached its daily processing capacity of 4.5 million trades. The IT problems also prompted the exchange to shorten its trading day by 30 minutes for what it said was "the foreseeable future."

Wednesday's early shutdown, the latest in a string of IT-related woes to hit the exchange, came after officials warned during the lunchtime break that trading would end if the volume of trades reached 4 million for the day.

In earlier incidents, faulty software caused erroneous trade orders, and trading was disrupted when a software patch was incorrectly applied to the exchange's trading system. Those problems prompted Takuo Tsurushima to resign as the exchange's president late last year.

"The exchange has been extremely active in promoting Internet trading, but on the other hand, they don't have the infrastructure ready to handle such surges [in trading volumes]," said Noriko Hama, a professor at the Doshisha University School of Management.

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