Thank you, Lisa, and good afternoon, everyone. 2018 was a strong year for AMD. New product introductions wrought the highest annual revenue since 2011 and a significant improvement in gross margin year-over-year. Earnings per share increased from $0.10 per share in 2017 to $0.46 per share in 2018. Full year 2018 revenue was $6.48 billion, up 23% year-on-year, driven by strong performance in the Computing and Graphics segment with significant growth in Ryzen processor sales. Although there was weakness in the graphics channel in the second half of the year, we saw strength in data center CPUs and GPUs. Gross margin was 39%, up 440 basis points from the prior year. Gross margin improvements are primarily driven by our new Ryzen, EPYC and Radeon products.
Operating expenses were 29% of revenue, an improvement of 2 percentage points from the prior year. For the full year, operating income was $633 million, up $409 million from $224 million in the prior year. Net income was $514 million, up $411 million, compared to net income of $103 million in the prior year. On the balance sheet, we reduced principal debt by $171 million and improved gross leverage significantly from 4.6x a year ago to 1.9x at the end of 2018. Let me turn to the details of the fourth quarter results.
Fourth quarter revenue gross margin, operating margin and earnings per share all improved year-on-year. Quarterly revenue of $1.42 billion was up 6% from a year ago. Strong sales of Ryzen and EPYC processors and data center GPUs more than offset lower channel GPU and semi-custom sales during the quarter. Fourth quarter 2018 revenue did not include any IP-related revenue, and blockchain-related GPU revenue was negligible.
Gross margin was 41%, up 740 basis points from 34% a year ago. Year-on-year gross margin improvement was driven primarily by the ramp of Ryzen and EPYC processor sales. Gross margin has increased year-over-year for 7 consecutive quarters, driven by a higher percentage of revenue from new products. Fourth quarter 2018 gross margin excludes a $45 million write-down of all the technology licenses that are no longer being used.
Operating expenses grew 9% year-over-year to $474 million and remained approximately flat as a percentage of revenue from the year-ago period. We continue to invest in our product road map and go-to-market activities as we gain market share in important markets. Operating income was $109 million, up $90 million from $19 million a year ago. Operating margin was 8%, up from less than 2% last year. Net income was $87 million compared to $8 million a year ago. Q4 2018 net income excludes a withholding tax refund plus interest of $43 million related to an IP litigation settlement from 2010. Diluted earnings per share using a diluted share count of 1,180,000,000 was $0.08 per share compared to $0.01 per share a year ago. Now turning to the business segment results.
Computing and Graphics segment revenue was $986 million, up 9% year-over-year. Revenue growth was driven primarily by continued strong Ryzen desktop product sales and the adoption of second-generation Ryzen mobile processors, largely offset by lower channel GPU and memory sales compared to the prior year. Ryzen products continued to ramp and were greater than 80% of total client revenue, driven by OEM and channel momentum. In graphics, sales were down year-over-year due to negligible blockchain-related revenue in the fourth quarter of 2018 as well as elevated levels of [ tropics ] inventory in the channel. Total graphics revenue grew sequentially, driven by strong Radeon data center GPU sales.
Computing and Graphics operating segment income was $115 million compared to $33 million a year ago. The increase was driven primarily by strength in Ryzen product sales and significantly higher ASPs in both desktop and notebook compared to a year ago. Enterprise, Embedded and Semi-Custom revenue was $433 million, flat from the prior year. Server revenue growth was offset by lower semi-custom revenue. EPYC processor units more than doubled sequentially, driving significant growth in data center revenue in the quarter. EESC segment operating loss was $6 million compared to a loss of $13 million a year ago. The improvement due to higher EPYC processor revenue was partially offset by lower semi-custom revenue and continued engineering and go-to-market investments in the server business.
Turning to the balance sheet. Our cash, cash equivalents and marketable securities totaled $1.16 billion at the end of the quarter. We generated free cash flow of $79 million in the quarter. Free cash flow was a negative $129 million for the full year primarily due to growth in inventory related to new products and the timing of collections. Inventory was $845 million, up $107 million sequentially, primarily due to the ramp of new products. Total principal debt was $1.5 billion as we further reduced term debt by $60 million during the [ fourth ] quarter, resulting in total debt reduction of $171 million during 2018. We expect to pay off the remaining $66 million of 2019 term debt in March 2019, and beyond that, there are no long-term debt maturities until 2022. Adjusted EBITDA was $152 million compared to $58 million a year ago, and on a trailing 12-month basis, adjusted EBITDA was $803 million, more than doubling year-over-year. Gross leverage was 1.9x as we ended 2018, and we are pleased to have achieved our long-term gross leverage target of less than 2x. Before turning to our financial outlook, let me discuss our Wafer Supply Agreement with GLOBALFOUNDRIES.
Today, the seventh amendment of the WSA spans from January 2019 through March 2024. It establishes purchase commitments and pricing at 12-nanometer and above for the years 2019 through 2021. The amendment also provides AMD full sourcing flexibility at 7-nanometer and beyond without any onetime payments or royalties for products purchased from other foundries. Turning to the outlook for the first quarter of 2019.
We expect revenue to be approximately $1.25 billion plus or minus $50 million, a decrease of approximately 12% sequentially and 24% year-over-year. Sequentially, the decrease is expected to be primarily driven by continued softness in the graphics channel and seasonality across the business. The year-over-year decrease is expected to be primarily driven by lower graphics sales due to excess channel inventory, the absence of blockchain-related GPU revenue and lower memory sales. In addition, semi-custom revenue is expected to be lower year-over-year while Ryzen, EPYC and Radeon data center GPU product sales are expected to increase. In addition, for Q1 2019, we expect non-GAAP gross margin to be approximately 41%, non-GAAP operating expenses to be approximately $480 million, non-GAAP interest expense taxes and other to be approximately $25 million, and we also expect to record a $60 million IP licensing gain associated with the THATIC JV in the first quarter of 2019, which will be a benefit to operating income and recorded on the licensing gain line of the P&L. For the full year 2019, despite near-term weakness in the graphics channel and a cautious macro environment, we expect high single-digit percentage revenue growth driven by Ryzen, EPYC and Radeon data center GPU product sales and as we ramp our 7-nanometer products throughout the year. We expect non-GAAP gross margin to be greater than 41%, non-GAAP operating expenses to be approximately 29% of revenue and a non-GAAP tax rate of approximately 4% of pretax income.
In closing, we made excellent progress in 2018. We grew the top line by more than $1.2 billion, expanded gross margin and significantly improved profitability. We continue to execute our long-term financial model, driven by our new high-performance computing products that gained solid momentum last year. We are pleased to enter 2019 with a strengthened balance sheet and a strong portfolio of next-generation products capable of driving continued financial growth. With that, I'll turn it back to Laura for the question-and-answer session. Laura?