Critical DDR333 modules
Although the 'Joint Electron Device Engineering Council', or simply JEDEC, has not yet released a standard for DDR333, the first corresponding modules are already on the market. It is strongly advised not to use DDR333 now.
You shouldn't get it yet, even if it's tempting immediately jump to the memory modules specified for 333 MHz (DDR), as they could be incompatible with current and future mainboards. The smooth mixed operation of DDR333 modules is also not guaranteed. It is best to wait a little longer and then buy appropriate modules from brand manufacturers such as Infineon or Micron. These will support the future standards of JEDEC and should work properly on all DDR333-compatible mainboards, even in mixed operation. Most of the current modules are basically overclocked DDR266 versions which then work in CL 2.5 mode and are therefore slower than CL2 DDR266 modules. This is possible because the JEDEC DDR266 standard is open at the top and does not set any limits for the manufacturers in terms of MHz. Thanks to Dominik Toth for the tip.