How Chime Works

by Eric Martz

Here is the sequence of events which occurs when you view a molecular graphic in Chime. The last two steps below may be the ones you are most interested in.

  1. When you start up Netscape, it inventories all the plug-in programs installed on your computer in Netscape's plug-ins directory, and records their MIME (Multi-purpose Internet Mail Extension) types in an internal table. You can view this table in Netscape by selecting Help, About Plug-Ins.

  2. You view a web page which uses Chime. An <embed ...> tag in the html document specifies either a source filename ending in .pdb, .spt, or another Chime-supported file type. The html document makes no explicit mention of Chime.

  3. Using its MIME table, the web server looks up .pdb or .spt and serves the file as MIME type chemical/x-pdb, chemical/x-spt, or another Chime-supported MIME type.

  4. Netscape looks up the MIME type of the file in its internal plug-in table and finds that it must run Chime.

  5. Chime is started up, creating a graphic area (usually black) embedded on the web page, of the size specified in the html document. Netscape hands the pdb, spt or other supported file to Chime.

  6. The atomic coordinate file (usually PDB) is sent from the server to the client (your PC). It may be compressed with a program named gzip to save Internet transfer time. If so, it nevertheless has a name ending in .pdb (although in fact it is no longer in PDB format), and is served as chemical/x-pdb. When Chime receives it, Chime detects that it has been gzipped and gunzips it automatically.

  7. Chime renders the image of the molecule. When you rotate (etc.) the image, Chime creates each image de-novo from the atomic coordinate file. The calculation of each image occurs entirely within your PC, by Chime, which has the atomic coordinates stored in your computer's memory. No Internet transfers occur while you are rotating or otherwise modifying the molecular image. The images themselves are never transferred through the Internet.

  8. When you click on a button, RasMol commands (also understood by Chime) are sent to Chime, changing the image. If the commands are specified within the web page html, no further Internet transfers are needed. If the command script is contained in a file (name ending in .spt), the server will transfer the command script file through the Internet to your client PC's Netscape (unless it was referenced previously, sent, and cached).

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