Time Zone Database

[Paul Eggert]

   From: "Clarissa Gammel" <cg at pc-plus.de>
   Date: Tue, 7 Apr 1998 09:59:44 PDT

   How often are there changes to the time difference information
   (approximately)?

It averages about once a month.  (But it's bursty.)

   How many countries are there with different time zones in one country?

That depends on how you count.  Do you mean different time zones now,
or different time zones at some point in history, or a differing set
of time zone histories?  It also depends on what you consider to be a
``country''.  Is Antarctica a country?

That being said, here's a list of countries in the current TZ database
that have multiple time zone histories.  The first column uses the ISO
3166 country code, the second is the number of time zone histories.
As you can see, Canada is the current champion, but this is to some
extent an artifact of the tz database's cutoff date of 1970.  The US
would undoubtedly be the real champion in a complete database.

$ awk '/^#/{next} {x[$1]++} END {for (i in x) if (x[i] != 1) printf "%s %2d\n", i, x[i];}' <zone.tab | sort +1nr +0
CA 21
US 20
RU 13
AU 10
BR  7
AQ  6
AR  6
CN  6
FM  4
MX  4
ES  3
GL  3
ID  3
KI  3
KZ  3
PF  3
PT  3
UM  3
CD  2
CL  2
EC  2
GB  2
IL  2
JP  2
MH  2
ML  2
MY  2
NZ  2
SJ  2
UA  2

   Who provides that information?

Volunteers.  Their mailing list is <tz at elsie.nci.nih.gov>.

   Is it a governmental institution? 

NCI is a governmental institution, but it's merely a host for the
mailing list.  The real source of info is volunteers.  The chief
volunteer is at NCI.

   When in general are the dates for those changes? Are they regular, or 
   each year different? Are there any rules?

Not really.

   Which countries do or don't have summer or winter time?

Generally speaking, the further you get from the equator, the more
likely you'll have daylight saving time.  But for the exact set of
countries at any point of time, you'll need to consult the database
at <ftp://elsie.nci.nih.gov/pub/>.