Why eats my Knoppix so much memory?

[user unknown]

My measurement:

Mem:    256336k total,    47744k used,   208592k free,     6856k buffers
Swap:   530104k total,        0k used,   530104k free,    24456k cached

  PID USER      PR  NI  VIRT  RES  SHR S %CPU %MEM   TIME COMMAND
  193 stefan    15   0  5968 2440 4968 S  0.0  1.0   0:00 bash
  194 postgres  15   0  5776 2432 4748 S  0.0  0.9   0:00 bash
  190 root      16   0  5736 2416 4748 S  0.0  0.9   0:00 bash
  319 postgres  16   0 16612 1940  15m S  0.0  0.8   0:00 postmaster
  325 postgres  19   0  7692 1744 6948 S  0.0  0.7   0:00 postmaster
  324 postgres  19   0  8684 1732 6948 S  0.0  0.7   0:00 postmaster
  404 root      16   0  6740 1708 5028 S  0.0  0.7   0:00 cupsd
  336 root      15   0  2928 1340 2164 S  0.0  0.5   0:00 xitami
  185 root      16   0  2384 1292 1360 S  0.0  0.5   0:00 klogd
  165 root      16   0  2400 1056 2024 S  0.0  0.4   0:00 pppd
  485 stefan    16   0  2064  960 1856 R  0.0  0.4   0:00 top
  180 root      15   0  2164  808 1608 S  0.0  0.3   0:00 pppstatus
  135 root      17   0  1732  676 1504 S  0.0  0.3   0:00 pump
  183 root      16   0  1700  632 1408 S  0.0  0.2   0:00 syslogd
  363 root      16   0  1528  504 1368 S  0.0  0.2   0:00 pppoe
  191 root      16   0  1640  472 1352 S  0.0  0.2   0:00 getty
  192 root      16   0  1640  472 1352 S  0.0  0.2   0:00 getty
  195 root      16   0  1640  472 1352 S  0.0  0.2   0:00 getty
    1 root      16   0    80   80   56 S  0.0  0.0   0:04 init
    2 root      34  19     0    0    0 S  0.0  0.0   0:00 ksoftirqd/0
    3 root       5 -10     0    0    0 S  0.0  0.0   0:00 events/0

SQL-Server: Postgres
HTTP-Servr: xitami
PHP: - none-

note:
- I didn't run any request for xitami and postgres.
- when I start X, and stop it, not all memory is shown as 'available'.

PS: Your server is now reponding in about 3 sec., even for the first request.