By Neil Hughes

Published: 09:00 AM EST (06:00 AM PST)

Apple on Wednesday suddenly removed its white entry-level MacBook from its website and online store, signaling that the five-year-old notebook has been officially replaced by the $999 MacBook Air [update: still available for eduction institutions only].

AppleInsider was first to report on Tuesday that Apple would begin to phase out the legacy device, first introduced as the successor to the PowerPC-based iBook and PowerBook. But the details from analyst Ming-Chi Kuo of Concord Securities suggested the discontinuation of the product would occur in the next few months.

Apple surprised on Wednesday when it suddenly pulled the white MacBook from its site, bringing a faster-than-expected transition to the new 11.6-inch MacBook Air as the only $999 notebook in Apple's lineup. Kuo, citing industry checks, revealed that Apple's internal forecast for the white MacBook suspiciously drops off in August of this year.

Monthly shipments for the Core 2 Duo MacBook had fallen to between 80,000 and 100,000 units, comprising less than 10 percent of the Apple's total Mac shipments in the first half of 2011.

Update: Apple has announced to resellers that its white MacBook, model No. MC516, is available for education institutions only. Channel backlog and non-direct education institution customers will see their orders canceled effective immediately. (Readers looking for one of these models can still purchase one from Mac Mall, which still reflects stock.

The MacBook will remain available to partners via Apple's online reseller stores only for education institutions. The company did not offer a timeframe for which the entry-level notebook will remain available.

AppleInsider first revealed in late June that supply of the white MacBook was severely constrained. Those stock-outs have persisted for weeks at resellers like Amazon.

The white polycarbonate MacBook was Apple's only $999 notebook for years, but that changed in 2010 when the redesigned MacBook Air was launched. That included a new entry-level 11.6-inch model at the same price point which found instant success on the market.

The MacBook Air offers some key advantages over the white MacBook, namely fast NAND flash memory for storage, an ultraportable thin-and-light design, and a durable aluminum unibody construction. But the MacBook also sports a larger 13-inch display, features an optical drive, includes a built-in Ethernet port, and has more hard drive space.