Path: utzoo!attcan!utgpu!jarvis.csri.toronto.edu!mailrus!cs.utexas.edu!uunet!portal!cup.portal.com!Don_A_Corbitt From: Don_A_Corbitt@cup.portal.com Newsgroups: comp.arch Subject: Re: *big iron* Message-ID: <22636@cup.portal.com> Date: 29 Sep 89 05:22:05 GMT References: <21962@cup.portal.com> <1989Sep12.031453.22947@wolves.uucp> <22130@cup.portal.com> <1989Sep16.044013.429@wolves.uucp> <259@ssp1.idca.tds.philips.nl> <22308@cup.portal.com> <7981@cbmvax.UUCP> <11538@burdvax.PRC.Unisys.COM> <22488@cup.portal.com> <3 Organization: The Portal System (TM) Lines: 52 Warning - posting from newcomer - Disk IO data enclosed System: Northgate 386 16MHz 4MB 32 bit memory on motherboard (paged - 0WS in page, else 1WS) RLL hard disk - 7.5MBit/sec transfer rate No RAM or disk cache Test 1 - How does transfer buffer size affect throughput under MS-DOS? Buffer RLL KB/s RAMDrive KB/s 512 156 446 1024 192 714 2048 284 1027 4096 352 1316 8192 409 1511 16384 445 1633 32768 471 1700 Test 2 - Using low-level calls, how does throughput differ? These are still the MS-DOS calls, but using read/write sector, not read/write file, commands. Buffer RLL KB/s RAMDrive KB/s 512 196 1245 1024 336 2203 2048 381 3206 4096 387 5266 8192 489 6526 16384 567 7367 32767 611 7856 Conclusion - it appears that MSDOS does a MOVSB to copy data from an internal buffer to the user area. I did the timing, and that almost exactly matched the speedup we see going from file IO to raw IO on the RAM disk. Note that this disk drive has a maximum burst transfer rate of 937KB/s, and a maximum sustained rate of around 800KB/s (assuming 0ms seek, etc). So we are able to get >1/2 max performance using the filesystem, and 3/4 of max using the low-level calls. Also, it appears that the memory-memory bandwidth is sufficient for anything that can get into a 32-bit 16 MHz slot. Of course, generic peripherals are looking at a 8MHz 16 bit slot with slow DMA. Don_A_Corbitt@cup.portal.com - this non-lurking could ruin my reputation PS - in 1984 I wrote the firmware for a 3.5" floppy drive with performance in mind - 1:1 interleave, track skewing, etc for the portable Tandy Model 100. It ran faster than any desktop PC I could find to benchmark it against. And I haven't noticed anyone making the effort to do the same since. So nobody cares about Disk IO?