Xref: utzoo comp.sys.ibm.pc:16141 comp.periphs:1003 Path: utzoo!utgpu!water!watmath!clyde!bellcore!rutgers!gatech!hubcap!ncrcae!ncr-sd!hp-sdd!hplabs!pyramid!octopus!pete From: pete@octopus.UUCP (Pete Holzmann) Newsgroups: comp.sys.ibm.pc,comp.periphs Subject: TECHNICAL DETAILS: Perstor RLL controllers Message-ID: <243@octopus.UUCP> Date: 5 Jun 88 15:10:14 GMT Reply-To: pete@octopus.UUCP (Pete Holzmann) Organization: Octopus Enterprises, Cupertino CA Lines: 111 Mark Fife (VP of ???) at Perstor read my RLL articles on the net and was kind enough to send me their official press releases, and some additional technical info. Based on an analysis of that info, I am writing two articles: this one, which talks about the new Perstor controllers, and another, which lists RLL-compatible drives. This article is intended to NOT be hype for Perstor. I am not duplicating their press release; my analysis will (hopefully) show the weak areas as well as the strengths. This article assumes prior knowledge: if you haven't read my previous article(s) on RLL technology, you may need to go find a copy and read it. I'm sorry, but I don't have a copy myself [the positive response to that article surprised me, to say the least!] First, some corrections to definitions: people call the Perstor drives 'ARLL' drives because they have the same data density (31/34 sectors per track) as what was originally called ARLL. Actually, Perstor appears to be using a normal 2,7 RLL data pattern. They are getting the increased data density by upping the clock rate, then compensating for the trouble that causes in other ways. Since this is not the same as ARLL, they have made up their own name: ADRT (Advanced Data Recording Technology, if you *must* know). I'll start with a short table showing some physical aspects of the different RLL technologies: Attribute 1,3 RLL 2,7 RLL 2,7 RLL 2,7 RLL (MFM) (normal RLL) (ADRT 1.8) (ADRT 2.0) Data rate 200ns/bit 150ns/bit 111ns/bit 100ns/bit (5MBit/sec) (7.5MBit/sec) (9MBit/sec) (10MBit/sec) clocks/bit 2 2 2 2 physical 100ns 75ns 55.5ns 50ns clock rate on drive min/max clocks 2/4 3/8 3/8 3/8 pulse-to-pulse on drive min/max time 200/400ns 225/600 167/444 150/400 between pulses on drive (leading edge) As you can see, there is no magic involved in the Perstor controllers. They DO push the drive's parameters pretty far. Some discussion: Clock rate on drive: This is directly related to that 'window margin' spec we talked about earlier. Obviously, Perstor controllers require much tighter window margins. Min/max time between pulses: by increasing the clock rate, the Perstor controllers get the maximum pulse interval closer to the original design time for MFM drives (400 ns), than does a normal RLL drive. The minimum pulse interval (high frequency rate) is much smaller than for MFM or normal RLL. The net result of these changes, especially since they are stressing the high frequency/high pulse density end of the specs, is that drives are more error-prone when data is written using the ADRT timing. Thus, in order to have a viable product, Perstor had to make compensating adjustments. Here's what they did: 1) Instead of using a normal 32 bit ECC, they use 56 bit ECC. This will more than compensate for the increased error rate expected, AS LONG AS THE DRIVE IS ABLE TO STORE *SOMETHING*. In other words, with increased storage density, more errors will result; but at some point, the head/recording surface simply can't keep up: the bits in error will go up to 100% (I supposes I should say 50%, since random bits will be right 50% of the time :-)). Thus, a need for... 2) Specify carefully which drives will work. Specifically, Perstor recommends: a) Hi resolution media (plated or the latest oxides) b) tight speed tolerance (old drives have 3% tolerance; Perstor requires 1%, preferable .5%, which is common on modern drives) c) Temperature range must be kept to 'typical operational environment' rather than 'extreme limits'. In other words, reduced temperature range from drive specs. CONCLUSION The net effect of this is that, as with 'normal RLL' controllers, MOST modern drives will work great with the Perstor controller. Some definitely will not. Any dealer hype to the contrary is just that. As far as I can tell, just about any drive that works with the Perstor controller will work fine on a 'normal RLL' controller, which is why the drive list in the next article is rather handy to have (thanks, Perstor!) Note that the Perstor controller is currently limited to 1024 cylinders. They are working on a new ROM that will handle more. That's it! Pete -- OOO __| ___ Peter Holzmann, Octopus Enterprises OOOOOOO___/ _______ USPS: 19611 La Mar Court, Cupertino, CA 95014 OOOOO \___/ UUCP: {hpda,pyramid}!octopus!pete ___| \_____ Phone: 408/996-7746