Path: utzoo!utgpu!jarvis.csri.toronto.edu!clyde.concordia.ca!uunet!wuarchive!mit-eddie!bu-cs!ngeow From: ngeow@bu-cs.BU.EDU (Yee Ngeow) Newsgroups: comp.sys.ibm.pc Subject: Transfer rates Message-ID: <44807@bu-cs.BU.EDU> Date: 17 Dec 89 01:10:15 GMT Reply-To: ngeow@cs.bu.edu (Yee Ngeow) Followup-To: comp.sys.ibm.pc Organization: Boston University Lines: 43 Hi! Just a question about hard disk transfer rates. I recently purchased a SCSI drive, the ST-02 (no flames please) and ST-157N. Running with the zero wait jumper enabled, with a 1:1 interleave I am getting 500K of transfer rate, but running at 2:1 I am getting 350K or so. I thought 1:1 is twice as fast as 2:1, since the disk must rotate twice to read all the sectors. Anyone know what is going on there? Also, how does one get the theoretical maximum transfer rate for any one encoding scheme (RLL/MFM/ESDI)? Doesn't the transfer rate be affected by the number of read/write heads you have on your drive? I though the sequence on sequential read/write on a hard disk is: (sector 0) head 0 1 2 3 .. (sector 1) head 0 1 2 3 .. (sector 2) head 0 1 .. It seems this way when I format a disk. So the more heads you have, the higher your transfer rate, since switching from head to head doesn't take any time?! Or is it the other way: (head 0) sector 0 1 2 3 4 ... 17 (head 1) sector 0 1 2 3 .... which provides a constant rate regardless of number of heads? Also, I though Winchester drives spin at a rate of 3000 revolution per second, as opposed to 300 rps on floppy drives. Assuming heads don't matter, the transfer rate formula on a 1:1 intereave is: 3000 * SECTOR/TRACK * SECTOR SIZE which will give me a HUGE number. Lets assume RLL, 26 sectors/track and 512 bytes/sector: 3000 * 26 * 512 = 39,000 Kbytes which is over 39 Megabytes/second, and is about 500 times greater then 7.5Mbits/second!! What is going on here??! I will appreciate if anyone can answer my question. Sorry if they seem naive, but I just can not figure it out.. Thanks in advance, Kwong