ags@pucc-i (Seaman) (06/13/84)
Don't make any assumptions about the speed of the drives on an Apple II unless you have used Apple Pascal. It is a MUCH faster disk operating system than (*choke*) Apple DOS. It is also faster than CP/M. -- Dave Seaman "My hovercraft is full of eels." ..!pur-ee!pucc-i:ags
ags@pucc-i (Seaman) (06/26/84)
I tried to respond to this by mail, but it didn't work. I said earlier that Apple Pascal is *much* faster on disk accesses than Apple DOS, and that it is also faster than CP/M. How much faster than CP/M? I don't have CP/M myself, so my information here is second hand. I do know that Pascal uses a "two-ascending" sector interleaving scheme, while CP/M uses "three-ascending". Two-ascending is guaranteed to be faster as long as you are not missing sectors and having to wait an extra full rotation. Pascal can do this because there is less intermediate processing going on during a block read. I don't have a reference handy and I can't quote any performance statistics, but I recall reading that Pascal beats CP/M on disk access, which is what you would expect when reading half the sectors that go by instead of a third. Apple DOS uses a "three-descending" interleaving scheme, which is equivalent to "thirteen-ascending" and means there is a LOT of waiting between sectors if you try to read them in ascending order. A common optimization scheme is to read the sectors in descending order to cut down on the wait time, but that still leaves you with the equivalent of a "three-ascending" scheme, the same as CP/M. As everyone knows, there is no free lunch. In order to get faster disk access, you have to give up something. In Pascal, what you give up is chaining; files are always allocated in sequential blocks instead of being strung randomly around the disk. This means you can occasionally run out of room on a file because space on the disk is fragmented. In practice, I have found that the problem is not serious (file compaction is quick and easy and does not have to be done very often) and I gladly make the tradeoff. There is a second benefit: because there are no chaining sectors, you get more space for actual data on each disk (274 out of 280 blocks to be exact, where a block is 512 bytes = 2 sectors, the smallest amount of data you can address on a Pascal disk). That leaves 2 blocks for a boot program and 4 blocks for the disk directory. The actual data storage per disk is 140,288 bytes out of 143,360. -- Dave Seaman "My hovercraft is full of eels." ..!pur-ee!pucc-i:ags
sdh@rabbit.UUCP () (06/30/84)
Sorry to contradict everything said so far, but THE fastest disk access for apple is using a routine called RWT. No that wasn't a typo. I do not mean RWTS. I mean Read/Write a Track. No sectors. Sectors slow the whole mess down. There is a trade-off: convenience v. speed. You have to copy these disks with a nibble copier, and its no good for multiple file handling. It is great if you need reams of data (say for a spelling correction program) very quickly. I know of no such markewted utility, so you'd have to write your own DOS. too bad. Steve Hawley <allegra,alice>!rabbit!sdh
barry@ames-lm.UUCP (Kenn Barry) (07/05/84)
[] Must correct the previous article - the DOS 3.3 skew is two- descending, and this is the fastest possible sector arrangement, *if* you patch DOS 3.3 so that the software is fast enough to read every other sector. Without the patch, DOS 3.3 misses its first chance at each sector and doesn't catch it 'til a full spin later. That's why it's so slooow.