Q I have heard of a better UART chip, the 16750. Do you know anything about this? Will it speed up my modem's throughput? And is it available in Australia?

A The UART chip is used by serial (com) ports. Most later model 486 computers, and all Pentium computers, come with at least a 16550A UART. This was an improvement over early designs because it included two buffers capable of storing 16 bytes each. When a serial device such as a modem is sending data to the serial port, while the computer is busy this information is temporarily stored in the buffer. This allows the serial port to work at faster speeds.

However, for new 56KBps modems and ISDN, the 16550A UART is just marginally too slow. Variations on the 16550A UART exist, and these include the 16650 UART, which has 32-byte buffers, and the 16750 UART, which uses 64-byte buffers. The maximum reliable transmission speed for the 16550A UART is 115.2KBps; for the 16650 the top speed is 230KBps, and for the 16750, 460KBps.

To get a faster UART you can purchase a serial port expansion card, but these are hard to find. Ringing round a few computer shops, I could not find anyone who sold a serial port expansion card with a 16750 UART; nor could I find anyone who knew what a 16750 UART was! However, there are sites overseas selling expansion cards with a 16750 UART, such as the TurboExpress Port 920 from www.pacificcommware.com/texport.html.

There are alternatives to buying a faster UART. An internal modem will not be held back by the speed of your serial port. For external devices, there are now USB ports as well as FireWire, and these were specifically designed to overcome the limitations of the serial port. But of course these require compatible devices.