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Low End Mac Tech Journal

Real World Mac Serial Throughput

Daniel Knight - 1999.09.03

Your results may vary, but this should provide a good starting point for tweaking serial throughput on your classic Mac setup. Note that FreePPP allows serial port settings of 115.2kbps and 230.4kbps, settings not possible with Apple’s serial toolbox routines.

Mac serial ports

Mac serial ports

For best possible throughput, don’t use your floppy drive, run CPU-intensive programs, or transfer data over LocalTalk and minimize use of the hard drive during serial port use.

68000-based Macs

Plus (8 MHz), reported by Rowland

  • 28.8kbps, some packet loss, best overall throughput
  • 19.2kbps, no packet loss, slightly lower throughput
  • packet loss at 57.6 kbps made throughput slower than at 9600bps

Plus (8 MHz, System 7.5.3), reported by Mike Friese

  • packet loss due to overruns, CRC errors beyond 19.2kbps

68020-based Macs

68030-based Macs

IIci (25 MHz), reported by Dirk von Seggern

  • 115.2kbps with few dropped packets using V.34+ modem
  • 64kbps throughput with ISDN at 115.2kbps

LC III (25 MHz)

  • 115.2kbps, unknown packet loss

Perfoma 460 (33 MHz), reported by Daryl Mitchell

  • 115.2kbps “works great” with 33.6 v.42bis modem

68040-based Macs

Centris 610 (20 MHz), System 7.5.5, FreePPP, OT 1.1.2, Supra 56e modem, reported by Dan Knight

  • 230.4kbps, one dropped packet, 88.4kbps throughput on statistics page for my ISP
  • 115.2kbps, no dropped packets, 83.2kbps throughput
  • 57.6 kbps, no dropped packets, 48.7kbps

Performa 475 (25 MHz), System 7.1 and 7.6, reported by Rowland

  • 115.2kbps

Centris 660av (25 MHz), System 7.5.5, FreePPP, OT 1.1.2, Supra 56e modem, 42-44kbps connection, reported by Dan Knight

  • 230.4kbps, few dropped packets, 88.5kbps throughput on statistics page for my ISP
  • 115.2kbps, no packet loss, 81.6kbps throughput
  • 57.6 kbps, no packet loss, 52.7kbps throughput

Quadra 650 (33 MHz), System 8.0, reported by Jonathan Ploudre

  • 230.4kbps, few dropped packets, 90kbps maximum throughput
  • 115.2kbps, no packet loss, 90kbps maximum throughput
  • 57.6 kbps, no packet loss, 49kbps maximum throughput
  • Gained 10-15% on sustained throughput by moving from 57.6 kbps to 115.2kbps.

Other Resources

Keywords: #macserialport #serialport