Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP Path: utzoo!utgpu!water!watmath!clyde!rutgers!husc6!necntc!ames!sdcsvax!ucsdhub!hp-sdd!hplabs!hp-pcd!uoregon!omepd!psu-cs!qiclab!neighorn From: neighorn@qiclab.UUCP Newsgroups: comp.unix.xenix Subject: Re: Wanted: Suggestion for 286==>386 Message-ID: <879@qiclab.UUCP> Date: Sun, 6-Dec-87 01:34:00 EST Article-I.D.: qiclab.879 Posted: Sun Dec 6 01:34:00 1987 Date-Received: Sat, 12-Dec-87 08:46:57 EST References: <7560@eddie.MIT.EDU> Reply-To: neighorn@qiclab.UUCP (Steve Neighorn) Organization: Qic Laboratories, Portland, Oregon. Lines: 73 In article <7560@eddie.MIT.EDU> mdc@eddie.MIT.EDU (Marty Connor) writes: > >I could also get a 386 machine and move the disk drives and such to >it; > > - Is it ok to use the 16 bit memory with a 386, or would I have to > buy a new 4 meg? > Whether or not you can use 16-bit memory on a 386 box is dependent on the box, but most of the 386-based AT platforms I have seen allow you to use 16-bit memory cards. A word of warning on using 16-bit memory cards in a '386 though: They are slow. Most of my experience in this area comes from using two iSBC 386AT boards from Intel. One system (catlabs - running Microport V/386) has 4.5 meg of memory - 512k of 32-bit memory on the motherboard, 2 meg of 32-bit memory in one of the 32-bit slots, and 2 meg of 16-bit memory on an Everex AT expansion card sitting in one of the 16-bit slots. The first thing you notice is while the machine is running the memory check, it blazes through the first 2.5 meg, then slows down while going through the next 2 meg. Microport (and I believe SCO Xenix) uses memory from low-to-high, leaving the unused memory at the top for user-memory. Microport allocates 1.3 meg for buffers, leaving me approximately 2.9 meg of user-memory. In my current configuration, that means about 1 meg of my user-mem is 32-bit memory and 2 meg is 16-bit. The lack of options on the 32-bit card and the Everex card prevent me from switching the cards so the 16-bit memory is used for buffers and the 2 meg 32-bit card is used for user-mem. I am unaware of any way to change the location of the buffer allocation, so it looks like, for the moment, I am stuck with the current configuration. Now the numbers: General testing (ie memory intensive programs, the venerable dhrystone bench, the MUSBUS bench stuff posted awhile ago) reveal that the 16-bit memory runs at about the same speed as 16-bit memory in a 6Mhz PC/AT. A look in my iSBC 386 manual shows the reason why: (A note - the iSBC386 uses dual-bank memory on the motherboard and the 32-bit memory slots. Only one wait-state is needed to access sequential memory in the alternating banks.) Operation CPU Clock at 16MHz Time --------- ------------------ ---- 32-bit (motherboard/32-bit slots): Read from alternating bank 3 187.5 Read from same bank 5 312.5 Write to alternate bank 4 250.0 Write to busy bank 6 312.5 ROM Read (two 16-bit accesses) 12 750.0 8-bit expansion slot read/write: 8-bit (PC-compatible slot) 8 500.0 16-bit (AT-compatible slot) 13 812.5 16-bit expansion slot read/write: 8-bit (PC-compatible slot) 8 500.0 16-bit (AT-compatible slot) 25 1562.5 32-bit expansion slot read/write: 8-bit (PC-compatible slot) 16 1000.0 16-bit (AT-compatible slot) 50 3125.0 Depending on the previous cycle, the 8/16/32 bit expansion operations might take an additional 62.5 ns clock cycle. If you are seriously thinking of getting an 80386 box, and speed is the name of the game, then spring for all the 32-bit memory you can get. My applications are such that more user-memory and larger buffers outweigh the slowness of the 16-bit memory. Good luck in your search. -- Steven C. Neighorn !tektronix!{psu-cs,reed,ogcvax}!qiclab!neighorn Portland Public Schools "Where we train young Star Fighters to defend the (503) 249-2000 ext 337 frontier against Xur and the Ko-dan Armada"