On <03 Nov 94 12:30> [EMAIL PROTECTED] wrote: Ia> On 03 Nov 94 04:35:00 +0000, Johnathan Taylor said: >> Hmm, that's a tricky one! On ProDos due >> to extensive cache'n ALL random-access >> positioning is calculated from scratch >> each time its required...
Ia> I thought ProDos wrote CP/M format Ia> disks, so why does it need to cache Ia> anything? Ever heard of banked cp/m+? That was the next general upgrade that allowed Least Recently Used (LRU) cache'n of both directory and data sectors seperatly. ProDos share them and only upto 16k worth but one benifit is if you are dealing with multiple open files some read and some write it makes sense to cache part read sectors before flush to get a different one for a different file access which save seeking back and forth as 128 byte records are read from each file at a time. Also as all sector reads go via the 16k LRU cache then a random-read to an earlier positon within the cache is Well fast as it involves no drive activity:-) Also with some programs which use multiple small files, apart from the intermediate dir checksumming to make sure the floppy hadn't changed since last access the actual data can be read straight from the cache! Ia> If my calculations are correct, an Ia> entire FAT would require 128K so caching Ia> it would be rather expensive and Ia> therefore random access would be rather Ia> slow. I'm definitely not in favour of a FAT-based system. Hmm, well at a minimum I guess one doesn't have to cache the entire FAT maybe a bit-map of it when first logged in which is maintained during file operations and a FAT only LRU cache page.... I'd need tech docs on the FAT system to propose a half-decent access method soooo.... I'll leave that upto the person who's writing it:-) If it turns out to be unacceptably poor in performance and Si's willing to do more to improve it then all well and good but if it functions correctly, just slow compared to other machines HD systems then AFAIC Si's quite at liberty to say "it works! what more do you want!" As I don't see anybody else taking the production of a HD system on a sam under the native system at all seriously esp Bob! A working system is a working system after all, if you despise FATs that badly develope your own filesystem and get Si to incorperate it if it fits the specs! Johnathan <[EMAIL PROTECTED]> ___ Olms 1.60 [Evaluation] +-------------------------------------------------------------------+ | Standard disclaimer: The views of this user are strictly his own | | ===> Gated @ Centronics BBS [centron.com] +44-1473-273246] <=== | +-------------------------------------------------------------------+
