command piped into bzip not using all available CPU

[Jim C. Nasby]

As you can see below, a command piped into bzip2 is only effectively
using one CPU. It's not disk bound, both systat and gstat report less
than 10% disk utilization. Why is this?

The command I'm running is: 
pg_dump -vZ0 ogr | bzip2 > ogr-20040416.sql.bz2

last pid: 18345;  load averages:  1.17,  1.09,  0.81  up 8+22:12:27  17:00:56
66 processes:  2 running, 64 sleeping
CPU states: 49.4% user,  0.0% nice,  3.7% system,  0.2% interrupt, 46.7% idle
Mem: 67M Active, 2935M Inact, 359M Wired, 331M Cache, 255M Buf, 5576K Free
Swap: 8192M Total, 64M Used, 8127M Free, 48K Out

  PID USERNAME PRI NICE   SIZE    RES STATE  C   TIME   WCPU    CPU COMMAND
17334 decibel  109    0 10856K  7164K CPU0   0  11:05 65.77% 65.77% bzip2
17335 pgsql      4    0   154M   124M sbwait 0   5:54 34.03% 34.03% postgres
17333 decibel   -8    0 20128K  3236K pipdwt 0   0:46  2.88%  2.88% pg_dump
-- 
Jim C. Nasby, Database Consultant                  jim at nasby.net
Member: Triangle Fraternity, Sports Car Club of America
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