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This article first appeared in the March 1999 issue of the Louisville Computer News. It was written by Lee Larson.
The motivation for this month's ramblings came from a conversation I had with an astronomer a few weeks back. Her work involves analyzing data from several radio telescopes in order to patiently tease out subtle differences between their signals. Since these telescopes are thousands of miles apart, the time stamp telling exactly when the data was received is almost as important as the data itself.
Not just any clock can time stamp such data. Differences measured in millionths of a second are important. They use atomic clocks, which measure time based on the precise tick of cesium atoms, and are accurate to within several millionths of a second per year.
The official time for the whole United States is regulated by a collection of a dozen or so atomic clocks maintained by the National Institute of Standards and Technology (NIST) in Fort Collins, Colorado. They keep time accurately to within a few billionths of a second per year. One of NIST's chief responsibilities is to let everybody else know what time it is. As technology has changed, they've added many ways for us to set our clocks.
Any shortwave radio listener can tell you about one of the first methods they used. The National Bureau of Standards, the predecessor of NIST, began broadcasting standard time on WWV from Fort Collins in 1923. Since then, they've added frequencies and transmitters. The main WWV signal can be heard on 2.5, 5, 10, 15 and 20 MHz. It has a sister station in Hawaii, called WWVH, which broadcasts on all these frequencies, except 20 MHz. A third station is of interest to computer users. WWVB broadcasts a specialized signal at 60 KHz, in the longwave band, which can be decoded by computers.
MultiMode from Black Cat Systems (www.blackcatsystems.com) is Macintosh software to decode WWVB signals. Theoretically, you should be able to set your Mac's clock to within a few hundredths of a second using MultiMode. Such accuracy is wasted, however, because the Mac's built-in time routines only have an accuracy of 1/60 of a second.
More recently, NIST has begun broadcasting the time from the global positioning satellite system (GPS). Anyone with an appropriate GPS receiver and software can set their clock to within a millisecond. Software to read the information from GPS receivers include GPS Pro (www.csn.net/~lwjames/GPSPRO.html) and GPSY (www31.pair.com/gpsy/).
Another way to read the NIST clocks is by telephone. They first added a voice line in the 1940's, and you can still get the real time of day with a voice message from them at (303)499-7111. It's nothing more than the WWV signal over the phone. More useful to modem users is NIST's Automated Computer Time Service (ACTS) at (303)494-4774. Dial into it with a regular terminal program and you'll get a series of lines similar to the following
D
L
MJD YR MO DA HH MM SS ST S UT1 msADV <OTM>
51224 99-02-15 00:37:48 00 0 +.7 045.0 UTC(NIST) *
51224 99-02-15 00:37:49 00 0 +.7 045.0 UTC(NIST) *
51224 99-02-15 00:37:50 00 0 +.7 045.0 UTC(NIST) *
Here's what it means. MJD is the last five digits of the Julian date, or the number of days since January 1, 4713 B.C. The next six columns give the date and time in UTC, a.k.a., Greenwich Mean Time. DST is Daylight Saving Time information. LS tells whether or not to add a leap second at the end of the month. The UT1 column is interesting because it shows how much accuracy we're dealing with here; it's the difference in seconds between clocks set by the earth's rotation and the actual time. The * in the OTM column is sent to mark the exact time, and the msADV column shows that the * was actually sent 45 milliseconds early to compensate for the delay in the modems and telephone line.
It's apparent that writing software to read this data and set your Mac's clock should be relatively easy. AutoClock 1.4.4 (macinsearch.com/infomac/cfg/auto-clock-144.html) is a nice freeware program to do just that. A short thirty second phone call to Fort Collins every few months keeps your Mac's clock within a few seconds of the correct time.
Finally, we get to the Internet. The Internet requires accurate time for many different purposes ranging from date stamps on mail to the real time transmission of audio and video. There are hundreds of easily accessible public time servers scattered all over the world which understand the Network Time Protocol (NTP). The information they provide is pretty much the same as that from the ACTS server shown above. Internet delays are cleverly corrected by averaging several round trip times from the server to the client, so accuracy within several hundredths of a second is normal.
The public time servers are divided into two classes, called primary and secondary servers. The primary servers are the most accurate since they have some very precise means of setting their clocks. The secondary servers set their clocks over the Internet by contacting primary servers. Even so, the accuracy of the secondary servers is very good. It is recommended that unless you have a good reason to do otherwise, you should only use the secondary servers. A list of many public time servers can be found at www.eecis.udel.edu/~mills/ntp/.
To access an NTP server, special software and an Internet connection are needed.
Starting with Mac OS 8.5, Apple built NTP client software into the Date and Time control panel. The NTP functions are clearly a first effort, because there are some limitations and oversights in Apple's implementation. For example, there is no way to accurately schedule an automatic update of the time from the control panel. Also, it shipped with a pretty bad bug; if you use NTP to correct the time on a Mac which is set to any time before 1964, it's likely to freeze your whole system.
There are alternatives.
The one I've been using for years is Vremya (www.download.com), a freeware program. The newest version, Vremya 2.0, can be configured to run at startup and then quit. My Mac clock is rarely more than a second off.
NetChronometer 1.3 (www.download.com) is a shareware NTP client with more features than Vremya. In particular, it can be scheduled more easily and writes out a log to tell you what it did.
On the other hand, Daemon 1.2 (www.stairways.com) is a freeware program to turn your Mac into an NTP server. It's useful for making sure all the machines on a local network have their clocks synchronized.
Apple released Macintosh Runtime Java 2.1 on February 13. MRJ 2.1 is Apple's implementation of Sun's Java 1.1.6. According to Apple: "MRJ 2.1 makes many improvements over Apple's previous Java virtual machines, including greatly increased performance, improved reliability, and support for AppleScript and Sun's JFC/Swing. MRJ 2.1 also runs more applications and applets than earlier versions."
Apple claims MRJ 2.1 is as much as five times faster than previous releases. Some quick tests confirm it is indeed much faster than MRJ 2.0, which already was much faster than the Java built into Netscape Navigator 4.5.
Apple makes an applet runner freely available, but most people will want to use MRJ 2.1 on the Web. To do this, Internet Explorer is necessary, rather than Netscape Navigator/Communicator. Netscape's browsers have their own Java built in and do not allow use of another implementation. Microsoft, on the other hand, has stopped shipping its own Java because of legal entanglements with Sun and requires use of somebody else's Java. There's a persistent net rumor that future versions of Navigator will also use MRJ.
MRJ 2.1 is an eight megabyte download from http://apple.com/macos/java/.
The Mac gaming community has been abuzz since early January over the Connectix Virtual Game Station, a Sony PlayStation emulator for the Macintosh. Sony quickly slapped a lawsuit on Connectix, claiming the improper use of intellectual property. On February 3, the San Francisco District Court rejected Sony's request for a restraining order on shipments. Connectix has already posted a program to update version 1.0 to 1.1 (www.virtualgamestation.com/updates.html).
Careful reading of the requirements shows that VGS won't run on just any Macintosh. The biggest requirement is that the Mac be a recent model with a fast bus. It's doubtful anything below a G4/233 would be pleasing. The graphical wizardry requires ATI graphics hardware, which is built into all G3 Macintoshes. In addition, VGS must be able to control the speed of the CD-ROM drive in order to quickly jump back and forth between sound mode at 1X speed and data mode at 8X speed.
I had a brief spin on an original 233 MHz iMac running the game Crash Bandicoot under VGS. Since I have a PlayStation and Crash Bandicoot at home, it was apparent that VGS does an adequate, but not spectacular job of turning an iMac into a PlayStation. The graphics were not as snappy, and the sound sometimes lagged a bit. The faster G3 machines should solve these problems.
Before you buy it, make sure it will play your favorite games. Connectix has a list of games that work on its web site (www.virtualgamestation.com).
Shoun Regan will present Connectix Virtual Game Station, the Sony PlayStation emulator and other games at the March 23 meeting of the Louisville Computer Society. All are welcome to attend.
The Louisville Computer Society meets on the fourth Tuesday of every month at Pitt Academy. Pitt Academy is at the intersection of Poplar Level Road and Gilmore Lane, 1.2 miles south of the Watterson Expressway.
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