标签: monitor

One advantage of punched cards over paper tapes was that the textual equivalent of the patterns of holes could be printed along the top of the card (one character above each column). Another advantage was that it was easy to replace any cards containing errors. However, the major disadvantage of working off-line (with both punched cards and paper tapes) was that the turn-around time to actually locate and correct any errors was horrendous. Generally speaking, if you make a programming error on one of today's interactive systems, the system quickly informs you of your mistake and you can fix it almost immediately. By comparison, in the days of the batch mode, you might slave for hours at a teleprinter with a card puncher attachment, march miles through wind and rain to the computer building carrying a one-foot high stack of cards, only to hear: "We're a bit busy at the moment, can you come back next Monday?" So you left your cards with the operator and spent the weekend in delightful anticipation, but on returning the following week to collect your results, you'd probably receive a few inches of computer printout carrying the words: "Syntax error on card 2: missing comma". Arrgggh – if the computer knew enough to tell that there was a missing comma, why didn't the callous beast know enough to stick one in for you? The result was that debugging even a trivial program could take weeks and weeks. In fact, by the time you eventually got a program to work, you were often hard-pushed to recall what had prompted you to write it in the first place! Although punched cards are rarely used now, we endure their legacies to this day. For example, the first computer monitors were constructed so as to display 80 characters across the screen. This number was chosen on the basis that you certainly wouldn't want to display fewer characters than were on an IBM punched card, and there didn't appear to be any obvious advantage to being able to display more characters than were on a card. Similarly, long after interactive terminals became commonly available, the formatting of certain computer languages continued to follow the rules laid down in the era of punched cards. To this day, many assembly languages have unnecessarily restrictive rules along the lines of "Labels can only occupy columns 1 through 8." Even the first high-level languages such as FORTRAN (an abbreviation of "Formula Translation") had comparable rules. As a final example, consider the case of the program called SPICE (Simulation Program with Integrated Circuit Emphasis) , which is used by engineers for evaluating analogue circuits. The first generation of this program appeared commercially around the beginning of the 1970s and its descendants are used to this day. The point is that it is still common practice to refer to the data used by this program as a "SPICE deck", which is a hangover from those times when such data was stored using punched cards ("deck of cards" – get it?). Perforated paper products never die... Finally, a word of caution. Perforated paper products never die, they simply fade away. Although the halcyon days for paper tapes and punched cards were certainly the 1960s and 1970s, do not be misled into believing that these media have completely exited the stage. In those days of yore, it was easy to spot anyone who had anything to do with computers, because their offices, briefcases, jacket pockets, and hands were usually overflowing with reels of paper tape and decks of punched cards ( "Holy paper products, Batman" ). However, although paper tapes and punched cards may seem delightfully antiquated, many institutions, including universities, continued to use these forms of data storage well into the 1980s, and both techniques are still to be found in the odd technological backwater to this day. Indeed, paper tapes continue to find a role to play in certain hostile environments. For example, in some manufacturing and heavy engineering facilities, computer-controlled machine tools may be located close to strong magnetic fields and electromagnetic noise. Many of today's storage technologies (such as floppy disks) tend to be corrupted in these conditions, but, much like the Energizer Bunny in the television commercials, paper tape products (especially modern varieties formed from materials such as Mylar) keep on going, and going, and going, and...