2 Why PCI?

Contents of this section

2.1 General overview

The PC-architecture has several BUS-Systems to choose from:

ISA

cheap, slow (usually 8Mhz), standard, many cards available>

EISA

expensive, fast, some cards available>

MCA

ex-IBM-proprietary, fast but not very wide-spread>

VESA-Local-Bus

based on ISA, cheap, fast, some cards available>

PCI-Local-Bus

expensive, fast, some cards available, the upcoming standard>

ISA/VESA-Local-Bus had some problems with high bus-speeds, and was not very reliable, but mainly due to its low price and better-than-ISA performance, sold very well. Most VESA boards should be stable by now.

EISA was reliable, but rather expensive, and intended more for power-users and servers, than for the average user. It has fewer cards available than other busses.

PCI now has the advantage. Like EISA it is not proprietary. It is as fast as EISA (or even faster), and 64bits wide. This will be important with the i586 (That Intel would prefer we call the Pentium...).

PCI is not like ISA/Local-Bus processor-dependent. This means you can use the winner-1000-PCI in an Alpha-driven-PCI-board as well as in a i486/i586-driven PCI-Board, except for the BIOS, but the hardware should be the very same.)

PCI allows cheaper production of onboard components, and needs no glue-logic chips.

2.2 Performance

taken from Craig Sutphin's Pro-PCI-Propaganda

Unlike some local buses, which are aimed at speeding up graphics alone, the PCI Local Bus is a total system solution, providing increased performance for networks, disk drives, full-motion video, graphics and the full range of high-speed peripherals. At 33 MHz, the synchronous PCI Local Bus transfers 32 bits of data at up to 132 Mbytes/sec. A transparent 64-bit extension of the 32-bit data and address buses can double the bus bandwidth (264 Mbytes/sec) and offer forward and backwards compatibility for 32 and 64-bit PCI Local Bus peripherals. Because it is processor-independent, the PCI Local Bus is optimized for I/O functions, enabling the local bus to operate concurrent with the processor/memory subsystem. For users of high-end desktop PC's, PCI makes high reliability, high performance and ease of use more affordable than ever before; no trivial task at 33 MHz bus-clock rates. Variable length linear or toggle mode bursting for both reads and writes improves write dependent graphics performance. By comprehending the loading and frequency requirements of the local bus at the component level, buffers and glue logic are eliminated.

2.3 The onboard-SCSI-II-chip NCR53c810

One very nice feature of some PCI mother boards is the NCR onboard-SCSI-II-chip, which is said to be as fast as the EISA-Adaptec-1742, but much cheaper. Drivers for DOS/OS2 are available. Drew Eckard has released version 3 of his NCR53c810-driver. I run kernel 1.1.78 at the moment (9JAN94).

This works so well I sold my adaptec-1542B-ISA months ago. :-)

The NCR53c810-chip is onboard on some PCI-motherboards. There are add-on-boards available too, for about US$ 70.00.

The NCR-patches and bootimages are available on tsx-11.mit.edu:/pub/linux/ALPHA/scsi/ncr (approximately). Newer releases of Slackware 2.0 have support for the ncr too. Newer versions of the test-kernels (1.1.41 for example) do not require any patches; they have the driver already included.

There is only one thing I noticed does not work with the current NCR-drivers yet. Disconnect/Reconnect does not work, so using a SCSI-tape can be a pain especially when using "mt erase" or the like blocks the whole SCSI-bus until it has finished. This is very unsatisfying.

I personaly use the NCR-driver at the moment, but I am inclined to shell out some money on the new DPT-boards mentioned in this article. (Michael Will, 09JAN94.)

2.4 Drew Eckhardt on PCI-SCSI:

Drew said some time ago about the SCSI on PCI: (slightly edited for clarity in context)

Currently, your only PCI SCSI option that stands a chance of working is the Buslogic 946. It purports to be Adaptec 1540 compatible, like the EISA/VESA/ISA boards in the series.

I'm working on getting the Linux NCR53c810 driver stable, some one else is doing the same thing for one of the BSD flavors.

This chip, offering fast busmastering, is included on motherboard implementations, and is (supposedly) available for US$ 100.00 on cards without BIOS (because many of the PCI boards that don't include the NCR chip onboard still do have the NCR BIOS).

This covers the majority of PCI SCSI adapters on the market (Nexstor, Chaintech, Gigabyte, FIC, etc). Adaptec is shipping (see below) a FAST WIDE version of the AIC-7770 with a PCI interface, and AIR is using it on their Pentium boards, but I haven't seen any separate board level product with it.

Scott Ferris is working on the AIC-7770 driver under Linux, but I don't know of anyone doing the same thing under one of the BSDs.

Emulux also has a propriety FAST+WIDE PCI controller. It's unlikely that it will show up as supported under one of the BSD's or Linux anytime soon, since the NCR based controllers are cheaper and more prevalent. Further, the NCR-equipped motherboards are often as cheap, or cheaper, than similar non-SCSI equipped boards.

The Buslogic PCI controllers are compatible with the 1540 (thus offering only that level of performance), so I doubt many Linux'ers will buy them.

Forex is shipping a PCI SCSI adapter, I don't have details.

Also note that since he said this, Drew has a working 810 driver out.

2.5 The EATA-DMA driver and the PCI SCSI controllers from DPT

The EATA-DMA scsi driver has undergone extensive changes and now also supports PCI SCSI controllers, multiple controllers and all SCSI channels on the multichannel SmartCache/Raid boards.

The driver supports all EATA-DMA Protocol (CAM document CAM/89-004 rev. 2.0c) compliant SCSI controllers and has been tested with many of those controllers in mixed combinations.

Those are:             (ISA)   (EISA) (PCI)
      DPT Smartcache: PM2011  PM2012A 
                              PM2012B 
      Smartcache III: PM2021  PM2022  PM2024 
                              PM2122  PM2124
                              PM2322 
      SmartRAID     : PM3021  PM3122  PM3224 
                              PM3222
      and some controllers from NEC and ATT.

On a "base" DPT card (no caching or RAID module), a MC680x0 controls the bus-mastering DMA chip(s) and the SCSI controller chip. The DPT SCSI card almost works like a SCSI coprocessor.

The DPT card also will emulate an IDE controller/drive (ST506 interface), which enables you to use it with all operating systems even if they don't have an EATA driver.

On a card with the caching module, the 680x0 maintains and manages the on-board cacheing. The DPT card supports up to 64 MB RAM for disk-cacheing.

On a card with the RAID module, the 680x0 also performs the management of the RAID, doing the mirroring on RAID-1, doing the striping and ECC info generation on RAID-5, etc.

The entry level boards utilize a Motorola 68000, the high-end, more raid specific DPT cards use a 68020, 68030 or 68040/40MHz processor.

Official list prices range from $245 to $1995 (December 1, 1994)

Since I've been asked numerous times where you can buy those boards in Europe, I asked DPT to send me a list of their official European distributors. Here is a small excerpt:

 
Austria: Macrotron GmbH            Tel:+43 1 408 15430   Fax:+43 1 408 1545 
Denmark: Tallgrass Technologies A/S Tel:+45 86 14 7000   Fax:+45 86 14 7333
Finland: Computer 2000 Finnland OY Tel:+35 80 887 331    Fax:+35 80 887 333 43
France : Chip Technologies         Tel:+33 1 49 60 1011  Fax:+33 1 49 599350
Germany: Akro Datensysteme GmbH    Tel:+49 (0)89 3178701 Fax:+49 (0)89 31787299
Russia : Soft-tronik               Tel:+7 812 315 92 76  Fax:+7 812 311 01 08
U.K.   : Ambar Systems Ltd.        Tel:+44 296 435 511   Fax:+44 296 479 461 

"IMHO, the DPT cards are the best-designed SCSI cards available for a PC. And I've written code for just about every type of SCSI card for the PC. (Although, in retrospect, I don't know why!) ;-)" Jon R. Taylor (jtaylor@magicnet.net) President, Visionix, Inc.

The latest version of the EATA-DMA driver and a Slackware bootdisk is available on: ftp.uni-mainz.de:/pub/Linux/Drivers/SCSI/EATA

Since patchlevel 1.1.81 the driver is included in the standard kernel distribution.

The author can be reached under these addresses: neuffer@goofy.zdv.uni-mainz.de or linux@uni-koblenz.de

2.6 Future Domain TMC-3260 PCI SCSI

Rik Faith (faith@cs.unc.edu) informed me on Wed, 1 Feb 1995 about the Future Domain TMC-3260 PCI SCSI card being supported by the Future Domain 16x0 SCSI driver. Newer information might be contained in the SCSI-HOWTO.

2.7 other thoughts on scsi

James Soutter (J.K.Soutter1@lut.ac.uk) asked me to add the following information on Fast-Wide-SCSI-2:

Fast Wide SCSI-2 is sometimes incorrectly called SCSI-3. It differs from the normal Fast SCSI-2 (like the Adapted 1542B?) because it uses a 16 bit data bus rather than the more usual 8 bit bus. This improves the maximum transfer rate from 10 MB/s to 20 MB/s but requires the use of special Fast Wide SCSI-2 drives.

The added performance of Fast Wide SCSI-2 will not necessarily improve the speed of your system. Most hard disk drives have a maximum internal transfer rate of less than 10 MB/s and so one drive alone can not flood a FAST SCSI-2 bus.

In Seagate's Oct 1993 product overview, only one Fast Wide SCSI-2 drive has an internal transfer rate of more than 10 MB/s (the ST12450W). Most of the drives have a maximum internal transfer rate of 6 MB/s or less, although the ST12450W is not the only exception to the rule. In conclusion, Fast Wide SCSI is designed for the file server market and will not necessarily benefit a single user workstation style system.

Rather than buying a PCI system with a SCSI interface on the motherboard, or rather than waiting for the NCR driver, you could purchase a separate PCI based SCSI card. According to Drew, the only PCI SCSI option that stands a chance of working is the Buslogic 946. It purports to be Adaptec 1540 compatible, like the EISA/VESA/ISA boards in the series.

Drew commented that other PCI based SCSI controllers are unlikely to be supported under Linux or the BSD's because the NCR based controllers are cheaper and more prevalent.

I personally would tend to try the NCR-Driver.

According to broom@ocean.fit.qut.edu.au (Bradley Broom):

The Buslogic BT-946C PCI SCSI works if you disable the option "enable Disconnection" with the AUTOSCSI-program under DOS which comes with the card.

Ernst Kloecker (ernst@cs.tu-berlin.de) wrote: (edited)

Talus Corporation has finished a NS/FIP driver for PCI boards with NCR SCSI. It will be shipping very soon, might even be free because a third party might pay for the work and donate the driver to NeXT.

Not every PCI-Board has got the chip. ASUS does, and one of the J-Bond boards does, too. Some vendors provide an alternative as you can read in Drew's text...

The NCR-Chip is clever enough to work with drives formatted by other controllers, and should be no problem.

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