Part 2 in response to why Macs use disk drivers and PCs (generally) don't.
Here follows a history of the PC platform's trials and tribulations with the hard drive through the years. Reading it is optional. Since the IBM PC was introduced in 1981 and the Mac in 1984 (and the PC was in development in the late 1970's) things naturally were more "primitive". Small hard drives that would be practical for use in a desktop computer didn't even exist until around about the time of the PC's introduction so it wasn't even possible to build support for them into the initial design. DOS was pretty much "ruled" by the ROM BIOS, the PC version of the Mac's ROM. (Since shortened to just BIOS with the advent of the Flash reprogrammable chip.) BIOS means Basic Input Output System. And it started out _really_ basic. When DOS wanted to read or write to a floppy, it called the routines from the BIOS. Everything in or out from basic peripherals was run by code called from BIOS and processed by the CPU. Fortunatly, IBM made a space in RAM where "option ROMs" could "plug in" and be called either by software programs or by standard commands sent to parts of that space in RAM. Video cards were the first devices to use that space, then hard drive controllers. Early PC hard drive controllers typically supported from as few as one to somewhere less than twelve specific models of drive, mostly because that's all there was available at the time, partly because PROM chips (Programmable ROM, write once only) cost a lot and using the smallest that would fit the code was cost effective. So with the hardware setup, the user booted from a DOS floppy then ran DEBUG and entered a command to access code in the controller's ROM. Select the right options, manually enter all the Bad Block data from the list printed on a lable on the top of the drive then sit back and wait for it to be formatted. Then the user could setup one or two partitions with FDISK, reboot then FORMAT the partitions, then use the SYS C: command to transfer over the three system files, IO.SYS MSDOS.SYS and COMMAND.COM IO.SYS and MSDOS.SYS had to be in specific locations at the beginning of the drive or DOS couldn't boot. All was well and happy in PC Land until 1984. It wasn't the introduction of the Mac that shook things up (as far as the low level hardware went) it was the IBM AT with the 80286 CPU and the introduction of CMOS RAM to store certain paramaters about the hardware like how much RAM was installed, the type of video card (color or mono) and most important the number of heads, cylinders and sectors per track of the new IDE hard drives. Again there weren't many models of drives available and most would fit a short list of parameters which amounted to around 47 different selections. Then things got hairy, really hairy. Drive manufacturers began to ignore the list of common parameters and were making bigger drives. To fix that some 3rd party companies wrote software that could make a drive that was the same size or close to one of the hard-coded BIOS types and "translate" the parameters so that when the BIOS called for data on a certain sector the software would interrupt the BIOS call and get the data from the drive then hand it to DOS while making it look like all was normal. This worked quite well, except that if the drive was moved to another computer it was unlikely that any of the data on it could be read because it would all be in the wrong sectors. Soon the PC makers added a user customizable hard drive entry to the BIOS so the actual drive parameters could be entered and the translation software was not needed. All was well again and DOS (plus Windows 3.0 running on top of DOS) could rely on the solid old BIOS calls again for any size and type of hard drive. (I'm leaving out SCSI on the PC here, that's a whole 'nother tale.) The PC world ticked along happily until hard drives hit then passed the 512 megabyte mark. There was a "little" problem in most of the different brands of BIOS that even if the user entered the correct drive parameters or the BIOS autodetction could properly see the drive's parameters, the BIOS would fail to inform DOS about anything more than 512 meg. The software workarounds with the same problem of not being able to move a drive to a different PC had to be dug up, wiped off and polished again. Sometimes, depending on what tricks the software had to do, it could be removed with the data intact after updating the BIOS or upgrading to a new motherboard with a BIOS that eliminated the 512meg limit. It was always a sticky thing, waiting for the successful completion. Wash, rinse, repeat. The BIOS programmers at American Megatrends, Phoenix, Award and the smaller companies did quick fixes for the 512meg limit. Unfortunately they didn't foresee the next filesystem Microsoft would unleash in 1996, FAT32, that smashed the old FAT16 2 gigabyte limit, so they only fixed the BIOSes for drives up to 2gig. The BIOS overlay software companies rejoiced again at the shortsighted PC world and made a boatload of money again. Do it again. So they "fixed" the 2gig limit, with an 8gig limit. See the previous paragraph. At each of those limits, there were a few PCs with a BIOS that could not be worked around with any sort of software trickery, so they either got upgraded motherboards or went to the trash, goodwill or were kept with their old drives. As far as I've seen and experienced, if there is any limit to har drive sizes on a PC now, this time they've made it so insanely huge that most PCs in current use really will be on the junkheap before the limit is hit. So you see, the Mac had a "head start" by starting later. Apple was able to create their own System and optimize the Mac to run just that. The PC's genesis began when the computer landscape was in a massive state of flux. IBM didn't even have an operating system chosen when they began the project because there wasn't anything anything like the PC at the time with the RAM capacity and the peripherals and expansion options they had planned for it. If IBM had loaded it up with a bunch of code it would have been just another limited box that wouldn't be much more than something like a Commodore PET with "massive" RAM and other storage options. IBM went for a design that would allow taking just about any OS and modifying it to work. They considered CP/M but Gary Kildall pretty much shot himself in the foot on that deal because he wasn't the type of guy who worked well with "stiffs" like the "Men In Blue". That left IBM with a computer ready for introduction but no software to run on it. Bill Gates just happend to be in the right place at the right time with enough knowledge of the CPU in the new IBM machine and he also happened to know of a fellow attempting to write a clone of CP/M to run on that CPU on a card plugged into an Altair or similar computer instead of the less powerful Z80. With a little careful "Yeah, we got what you need." his future was made and it's had an enormous impact for good or ill on just about everyone. ===== http://www.junkscience.com "All the Junk that's fit to Debunk!" __________________________________________________ Do You Yahoo!? Yahoo! Health - Feel better, live better http://health.yahoo.com -- Vintage Macs is sponsored by <http://lowendmac.com/> and... 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