Last October, I said it was a bad idea to invest in HP (NYSE:HPQ) because its rising PC sales were temporary and its printing business was stuck in a secular decline. I said the tech giant was treading water with buybacks, and its weaknesses would eventually overwhelm its strengths. But since I wrote that article, HP's stock price has rallied nearly 70% as the S&P 500 has advanced less than 20%. Let's see what I got wrong, and whether or not it's too late to buy HP after its surprising gains. Has HP overcome its biggest problems? HP generated 69% of its revenue from its Personal Systems business, which sells notebooks, desktops, and workstations, in fiscal 2020. The remaining 31% came from its printing business, which sells printers and supplies.