Cash and cash equivalents primarily consist of deposits held at major banks, money market funds and other securities with original maturities of 90 days or less. Marketable securities consist of time deposits and certain other securities.

The amortized principal amounts of our cash, cash equivalents and marketable securities approximated their fair values at May 31, 2022 and 2021. We use the specific identification method to determine any realized gains or losses from the sale of our marketable securities classified as available-for-sale. Such realized gains and losses were insignificant for fiscal 2022, 2021 and 2020. The following table summarizes the components of our cash equivalents and marketable securities held, substantially all of which were classified as available-for-sale:

As of May 31, 2022 and 2021, substantially all of our marketable debt securities investments mature within one year. Our investment portfolio is subject to market risk due to changes in interest rates. As described above, we limit purchases of marketable debt securities to investment-grade securities, which have high credit ratings and also limit the amount of credit exposure to any one issuer. As stated in our investment policy, we are averse to principal loss and seek to preserve our invested funds by limiting default risk and market risk.

Restricted cash that was included within cash and cash equivalents as presented within our consolidated balance sheets as of May 31, 2022 and 2021 and our consolidated statements of cash flows for the years ended May 31, 2022, 2021 and 2020 was nominal.