mamon@acf4.UUCP (Gary Mamon) (11/11/86)
Hi there!
We are interested in acquiring an AT clone, and looking at the literature
brings up the following questions (and also shows the extent of my ignorance):
1. Why do some machines have two or more clock-times available? Shouldn't
one want the largest clock rate when any choice is available?
2. Some advertisors indicate: "640k RAM on Motherboard". Is this memory
THE memory of the machine, or does it simply indicate the amount which the
memory can be expanded to?
3. Can Xenix be run on any clone? Does it work well (i.e., is the total
machine performance significantly reduced when two or more users or tasks
are competing for CPU?).
Gary A. Mamon ---> Astrophysics Group, New York University Physics Department
(212) 598-3627 +++++++ 4 Washington Place, New York, NY 10003, USA
USENET: {allegra|ihnp4|seismo|princeton|topaz}!cmcl2!acf4!mamon
ARPANET: mamon@nyu-acf4.arpa
BITNET: ARPA%"MAMON@NYU-ACF4.ARPA"ballou@brahms (Kenneth R. Ballou) (11/18/86)
In article <13210001@acf4.UUCP> mamon@acf4.UUCP (Gary Mamon) writes: >Hi there! Hello. >We are interested in acquiring an AT clone, and looking at the literature >brings up the following questions (and also shows the extent of my ignorance): Better to ask the questions now. And no, it does not show you to be ignorant! >1. Why do some machines have two or more clock-times available? Shouldn't >one want the largest clock rate when any choice is available? Not always. The vast majority of software will run at the higher speed. However, some screwy copy-protection schemes will fail at the higher speed and succeed at the lower one. Also, some of the more inexpensive peripherals become very unhappy at the higher speed. For example, I have an internal modem which works fine at 6 MHz but which is literally invisible to the system at 12 MHz. This is not unreasonable, since peripherals do not necessarily expect to have the bus driven at such a speed, even if they aim to be IBM compatible. (What a thought, IBM coming out with a fast microcomputer!) >2. Some advertisors indicate: "640k RAM on Motherboard". Is this memory >THE memory of the machine, or does it simply indicate the amount which the >memory can be expanded to? Neither, exactly. The AT's memory can be expanded to 16M, although that won't do you a whole lot of good under current DOS (well, 15M worth of RAM disks :-). This tells you how much memory is in the machine when you first take it out of the box. To expand the memory beyond what is on the motherboard, you will need to purchase an expansion card. Usually these cards give you space to plug in up to 3M of RAM chips. >3. Can Xenix be run on any clone? Does it work well (i.e., is the total >machine performance significantly reduced when two or more users or tasks >are competing for CPU?). It works on my machine. It's fairly good at 6MHz and an absolute joy at 12 MHz. By the way, allow me to give you some unsolicited advice. I have a PC's Limited 286-12 and am thoroughly delighted with the machine. I have had literally *ZERO* difficulty with it and have found no compatibility problems so far. I wouldn't hesitate for a moment to recommend the machine to you. I will, however, pass along one remark. Don't forget that a higher clock speed may upset some peripherals. In particular, if and when you decide to add memory to your system (and if you are running XENIX, you will), you may find you need to get faster RAM than is used in 6 or 8 MHz machines. Personally, I find the extra speed well worth it. -------- Kenneth R. Ballou ...!ucbvax!brahms!ballou Department of Mathematics ballou@brahms.berkeley.edu University of California Berkeley, California 94720
berger@clio.UUCP (11/19/86)
Some software is (badly) written to depend on software timing loops. It will only perform properly if the machine uses the same clock speed, thus, you may want to be able to run at 6 MHz even if your machine will normally run at 12 MHz.
ben@catnip.UUCP (Bennett Broder) (11/20/86)
In article <332@cartan.Berkeley.EDU> ballou@brahms (Kenneth R. Ballou) writes: >>3. Can Xenix be run on any clone? Does it work well (i.e., is the total >>machine performance significantly reduced when two or more users or tasks >>are competing for CPU?). > It works on my machine. It's fairly good at 6MHz and an absolute joy >at 12 MHz. But it won't run on all clones. Xenix requires parity checked memory. I am not aware of a particular AT class machine that doesn't have it, but the Tandy 1000 PC compatible doesn't and hence can't run Xenix. You might even want to call your Xenix vendor (SCO or IBM) to see if they have had any experience with the machine you are considering. -- Ben Broder {ihnp4,decvax} !hjuxa!catnip!ben {houxm,topaz}/
kc@rna.UUCP (Kaare Christian) (11/21/86)
>3. Can Xenix be run on any clone? Does it work well (i.e., is the total >machine performance significantly reduced when two or more users or tasks >are competing for CPU?). When I reviewed SCO Xenix System V for PC mag last Spring I had three AT's at my disposal: Mfr. Disk Ctrl. Speeds Motherboard A Red River Tech DTC 6,8,10 Chipset A PC Designs WD 6,10 Random IBM WD 6 Random The Red River machine was the first on the market with the Chips and Technology chipset, but today Red River is out of business. Other machines currently use the chipset. PC Designs is still in business, and IBM is doing well. Anyway I couldn't get Xenix to *boot* from boot floppy on the RRT machine until I swapped in a Western Digital controller. Then it booted fine, and I was then able to replace the WD with the original DTC and it still worked fine. Once running I could tar to/from floppy on RRT using the DTC controller, so it isn't a gross problem, rather the original system installation process picks up some subtle difference between WD and DTC. Moral 1 : Although the DTC disk controller works with DOS, there is some incompatibility with Xenix. Stay with the WD disk controller. Moral 2 : Apparently Xenix cohabitates well with the Chipset, which is the basis of many current clone motherboards. I also tried Xenix at all of the available speeds on all of the systems. It booted from wini at all speeds, and worked reliably at all speeds. Moral 3 : Get a fast one. (Especially the disk. Do not even consider an XT type 60-90ms. disk. You need a 30-40ms. hard disk.) As to performance, fast is better but even 6 MHZ is pretty respectable. Some benchmark info appears in the article (PC Magazine, August 1986). You can get a reprint from SCO. The bottom line is that a 10MHZ AT running Xenix has about one half of the performance of a VAX 780: equal integer performance, much slower floating point, slower I/O. You could support several people doing light work or one heavy user. Based on my experiences, I believe that Xenix is compatible with most clones, but of course you can get bitten. I had lots of spare widgets around, which makes it easier to cobble something together when one widget is slightly incompatible. You should also keep in mind that Unix software is much better behaved than DOS software. In the DOS world there were many programs that wouldn't boot at above 6MHZ, programs like copy2pc and copywrite are unbelievably machine specific, and copy protection gets you every other time. In the Xenix world, once the operating systems works your compatibility problems are mostly over. In the DOS world booting DOS is easy, but getting [ your favorite misbehaved/copy-protected DOS program ] to work can be impossible. Kaare Christian cmcl2!rna!kc