bjorn@alberta.UUCP.UUCP (02/03/87)
In <985@ulowell.cs.ulowell.edu> (Paul Dickson) writes: >As to a MMU, well at the AAUG meeting, RJ Mical mentioned that if you >add something to a product that costs 00, the consumer ends up paying >up to 00 for it. That's one reason we won't see the 68020 with MMU for >a while. Also, if you add an MMU to a 68000, you loose performance. >These reasons are why Amiga decided not to put in the MMU. This particular smoke-screen is clear as mountain air. It may be true about the price to the public, although I have my doubts (ie. I find it hard to believe that ALL additions to a design show up linearly in the cost to consumer). On the other hand there's absolutely no reason in the world to buy Motorolas MMU if it's thought to be too expensive, after all hardly anybody uses the thing anyway. Many companies using 68k's have happily built their own MMUs out of static ram or NS32k parts, etc., even some with software doing the TLB refilling. These same companies had no choice, since Mot. has been late in delivering MMUs for years. I suggest that the proper place for an MMU is at the heart of a computer system. It's to Sun Microsystems credit to have taken exactly that view. Most systems with an MMU allow it to be turned off, that takes care of your speed argument. Now I'll bring in a speed arguments of my own: Just how efficiently are you able to use the memory in your machine (fragmentation anyone?), how long do you have to wait till the processes in execution finish up so that you have enough contiguous memory to run another process. Just how much does it speed up your work, when your machine crashes taking some of your work down with it, or even if it doesn't trash your work, how long to reboot and set up your environment? How long does it take you to fix the damage done by a Trojan horse program or a faulty commercial program on your unprotected computer? Do you want me to continue? There are reasons why computers that lack a reasonable resource control device can be sooooooo unpleasant to use at times!!! A bicycle with brakes is a little slower and heavier than one without. Leaving out the brakes is fine for special applications, but is not recommended for general street use. Support strategic defense for PCs, Bjorn R. Bjornsson alberta!bjorn