MACINTOSH POWERBOOK DUO 210 and INTERNAL EXPRESS MODEM
As an option, Apple offers an internal modem for the DUO powerbooks. The modem offers high performance (V.32bis/V.42/V.42bis/MNP2-5/fax), but an interesting feature of its design is that it uses the DUO host processor for some tasks such as error correction and data compression. This reduces the modem's cost, complexity and size, but one naturally wants to know if the use of the host processor reduces performance in any way. My preliminary experience indicates that a slight performance degradation is indeed there.
Here is the test: receive a large file from a remote host using Zmodem and see what kind of transfer rate is reported. The baseline performance is established by using a Mac II with external Supra V.32bis FaxModem. Comparison machine is Mac PowerBook Duo 210 (w/CPU clock at 25 MHz) with internal Apple Express Modem. The remote host is a UNIX workstation accessed via Annex box and a V.32/V.42/V.42bis modem connection (i.e. V.32 carrier at 9600 bps, V.42 error correction and V.42bis data compression), with no other users at the time of the test. Two files were received: a 160Kb text file, and a 110Kb binary executable file. Both were compressible. Here are the results reported by Zmodem:
FILE: Mac II/Supra: Duo 210/internal:
160 Kb text 2025 cps (210%) 1780 cps (185%)
110 Kb binary 1825 cps (190%) 1695 cps (172%)
Above, "210%" indicates data compression effectiveness (given 9600 bps carrier).
From this test, the Duo 210/internal combination appears about 10% slower than the baseline Mac II/Supra system. This small performance reduction is likely to be even smaller in a Duo 230, which uses a faster 33 MHz processor.
Overall, the Express Modem from Apple is a nice package, with elegant fax software, slightly lower performance than ideal when data compression makes demands on the host processor. One problem: ring detection (eg. to automatically receive a fax) appears to be unreliable for unknown reasons (maybe I need to study the manual more). Manual receive works just fine, though.
