After Charles Darwin’s book The Origin of the Species was published, the German zoologist Ernst Haeckel stated that “Ontogeny Recapitulates Phylogeny.” By this he meant that the development of an embryo (ontogeny) repeats (i.e., recapitu1ates) the evolution of the species (phy1ogeny). In other words, after fertilization, a human egg goes through stages of being a fish, a pig, and so on before turning into a human baby. Modern biologists regard this as a gross simplification, but it still has a kernel of truth in it.
Something analogous has happened in the computer industry. Each new species (mainframe, minicomputer, personal computer, embedded computer, smart card, etc.) seems to go through the development that its ancestors did. The first mainframes were programmed entirely in assembly language. Even complex programs, like compilers and operating systems, were written in assembler. By the time minicomputers appeared on the scene, FORTRAN, COBOL, and other high-level languages were common on mainframes, but the new minicomputers were nevertheless programmed in assembler (for lack of memory). When microcomputers (early personal computers) were invented, they, too, were programmed in assembler, even though by then minicomputers were also programmed in high-level languages. Palmtop computers also started with assembly code but quickly moved on to high-level languages (mostly because the development work was done on bigger machines). The same is true for smart cards.
Now let us look at operating systems. The first mainframes initially had no protection hardware and no support for multiprogramming, so they ran simple operating systems that handled one manually-loaded program at a time. Later they acquired the hardware and operating system support to handle multiple programs at once, and then full timesharing capabilities.
When minicomputers first appeared, they also had no protection hardware and ran one manually-loaded program at a time, even though multiprogramming was well established in the mainframe world by then. Gradually, they acquired protection hardware and the ability to run two or more programs at once. The first microcomputers were also capable of running only one program at a time, but later acquired the ability to multiprogram. Palmtops and smart cards went the same route.
Disks first appeared on large mainframes, then on minicomputers, microcomputers, and so on down the line. Even now, smart cards do not have hard disks, but with the advent of flash ROM, they will soon have the equivalent of it. When disks first appeared, primitive file systems sprung up. On the CDC 6600, easily the most powerful mainframe in the world during much of the 1960s, the file system consisted of users having the ability to create a file and then declare it to be permanent, meaning it stayed on the disk even after the creating program exited. To access such a file later, a program had to attach it with a special command and give its password (supplied when the file was made permanent). In effect, there was a single directory shared by all users. It was up to the users to avoid file name conflicts. Early minicomputer file systems had a single directory shared by all users and so did early microcomputer file systems.
Virtual memory (the ability to run programs larger than the physical memory) had a similar development. It first appeared in mainframes, minicomputers, microcomputers and gradually worked its way down to smaller and smaller systems. Networking had a similar history.
In all cases, the software development was dictated by the technology. The first microcomputers, for example, had something like 4 KB of memory and no protection hardware. High-level languages and multiprogramming were simply too much for such a tiny system to handle. As the microcomputers evolved into modern personal computers, they acquired the necessary hardware and then the necessary software to handle more advanced features. It is likely that this development will continue for years to come. Other fields may also have this wheel of reincarnation, but in the computer industry it seems to spin faster
No comments:
Post a Comment