Path: utzoo!mnetor!uunet!husc6!uwvax!oddjob!mimsy!umd5!ames!ucbcad!ucbvax!cbosgd!mandrill!nitrex!rbl From: rbl@nitrex.UUCP ( Dr. Robin Lake ) Newsgroups: comp.unix.wizards Subject: Re: /dev/swap - possibility of it being a ramdisk Message-ID: <586@nitrex.UUCP> Date: 16 Dec 87 13:21:45 GMT References: <712@qetzal.UUCP> <585@nitrex.UUCP> <17013@topaz.rutgers.edu> Reply-To: rbl@nitrex.UUCP ( Dr. Robin Lake ) Organization: The Standard Oil Co., Cleveland Lines: 28 In article <17013@topaz.rutgers.edu> ron@topaz.rutgers.edu (Ron Natalie) writes: >Say what? On PDP-11's UNIBUS attached disks can not possilby have >17,000 times the transfer rate of conventional disks. The whole >bandwidth of the bus is 2.2MB per second in the best of cases. Most >drives even in days gone by could approach a 1MB/s. What you don't >have is the seek latency. > >-Ron It depends upon what the transfer rate and interleave factor of the "conventional disks" are. The solid-state RF-11/RS-11 disk equivalent was invented in the summer of 1970. There were few head-per-track disks from DEC at that time (as I recall, the one adapted from the PDP-8 and PDP-12 lines was 32Kbyte or 64K bytes) and the low bit density led to slow transfer rates. So.... it's all a question of the denominator. The controller on the Monolithic Systems "EMU" (Extended Memory Unit) was capable of doing multiple DMA disk transfers in a single bus request, which pushed the transfer rate right close to the Unibus limit. I've forgotten what we got for the peak transfer rate, but I vaguely remember a hair above 2 Mb/sec. (8 times 256 K words in a data acquisition application using a dual-port "EMU"). Rob Lake -- Rob Lake {decvax,ihnp4!cbosgd}!mandrill!nitrex!rbl