We regularly invest in non-marketable equity investments of private companies, which range from early-stage companies that are often still defining their strategic direction to more mature companies with established revenue streams and business models. The carrying value of our non-marketable equity investment portfolio, excluding equity derivatives, totaled $3.4 billion at December 29, 2007 ($2.8 billion at December 30, 2006) and included our investment in IMFT of $2.2 billion ($1.3 billion at December 30, 2006). Our non-marketable equity investments are classified in other long-term assets on the consolidated balance sheets.

Non-marketable equity investments are inherently risky, and a number of these companies are likely to fail. Their success is dependent on product development, market acceptance, operational efficiency, and other factors. In addition, depending on their future prospects and market conditions, they may not be able to raise additional funds when needed or they may receive lower valuations, with less favorable investment terms than in previous financings, and our investments would likely become impaired.

We review our investments quarterly for indicators of impairment; however, for non-marketable equity investments, the impairment analysis requires significant judgment to identify events or circumstances that would significantly harm the fair value of the investment. The indicators that we use to identify those events or circumstances include:

• the investee's revenue and earnings trends relative to predefined milestones and overall business prospects;
• the technological feasibility of the investee's products and technologies;
• the general market conditions in the investee's industry or geographic area, including adverse regulatory or economic changes;
• factors related to the investee's ability to remain in business, such as the investee's liquidity, debt ratios, and the rate at which the investee is using its cash; and
• the investee's receipt of additional funding at a lower valuation. If an investee obtains additional funding at a valuation lower than our carrying amount or a new round of equity funding is required for the investee to remain in business, and the new round of equity does not appear imminent, it is presumed that the investment is other than temporarily impaired, unless specific facts and circumstances indicate otherwise.

Investments that we identify as having an indicator of impairment are subject to further analysis to determine if the investment is other than temporarily impaired, in which case we write down the investment to its estimated fair value. For non-marketable equity investments that we do not consider viable from a financial or technological point of view, we write down the entire investment, since we consider the estimated fair value to be nominal. Over the past 12 quarters, including the fourth quarter of 2007, impairments of non-marketable equity investments have ranged between $10 million and $44 million per quarter.