Cream of the Crop 20/Cream of the Crop 20 (Terry Blount) (1996).iso/os2/pcii0696.zip/PCIFAQ.TXT

Text File | 1996-06-08 | 22KB | 456 lines

          Document:  PCI Frequently Asked Questions list
        Maintainer:  Patrick Duffy, [e-mail]
    Revision Dates:  9/13/95, 11/26/95, 5/18/96, 5/26/96
       Archived at:  ftp.netcom.com, in directory /pub/ab/abe/
                     CompuServe (GO BENCHMARK)
         Web pages:  http://warp.eecs.berkeley.edu/os2/workbench/work.htm
                     http://www.os2forum.or.at/english/info/os2hardwareinfo/
                     (note that the first URL may not have up-to-date
                     versions of the lists)

This document is intended for use by individuals and corporations in a
non-commercial manner.  It may be distributed freely within those
limitations.  Commercial use of this document in any manner requires
prior written permission of the author.

This is the PCI Frequently asked Questions list. It is designed to
provide a beginning guide to what is turning out to be the dominant bus
standard among PCs. It attempts to answer all of the following
questions: Dates in brackets indicate the last revision date for the
related entry.

1) What's PCI?

2) How does the PCI bus compare with:
   a) ISA
   b) EISA
   c) VL
   d) MCA

3) What are the features of the various PCI revisions?
   a) 2.0
   b) 2.1

4) How can I obtain more information about the PCI specification?
   a) How to obtain the PCI specification
   b) How to obtain more general information

5) I've heard that many new PCI chipsets support EDO RAM.  What is EDO
   RAM and how will it benefit me?

6) I would like my new Pentium system to use parity RAM.  Which chipsets
   will make use of parity RAM?

7) How fast is the PCI bus running in my system?

8) I'm upgrading from an ISA/VL/EISA system:
   a) What will still work in my new system?
   b) What do I not need to replace?
   c) What should I consider replacing?
   d) When using a PCI motherboard, if i don't replace my sound
      and I/O card won't it slow down the PCI board?
   e) What types of motherboards will work best?
   f) How much faster will my new system be?

------------------------------------------------------------------------

1) What's PCI? (5/18/96)

PCI, or Peripheral Component Interconnect is, briefly, a new way of
interconnecting the peripherals (cards you plug into the motherboard)
with both the system memory and the CPU.  It was designed from the start
to alleviate many of the headaches that installation of a new card into
an ISA bus-based computer would cause (IRQ conflicts, address conflicts,
etc.).  All PCI standards are set by a committe to ensure wide industry
support.  Some of its major features:

   a) Multiple busmasters on the same bus.  (Several SCSI controllers
      running at the same time, for example.)

   b) Auto-configuring.  All components which plug into the PCI bus will
      be configured by the BIOS, making jumpers for this unnecessary.

   c) IRQ sharing.  The PCI bus is able to share a single interrupt
      between cards.

   d) High bus bandwidth.  The PCI bus runs at a maximum rate of 33 MHz
      (66 MHz in PCI 2.1 -- see later) and is capable of transferring 32
      bits (4 bytes) per clock cycle, for a maximum throughput of 132
      (264 in PCI 2.1) MB/sec (though bus latency times usually lower
      this to significantly less than maximum in real implementations).

   e) Multiple functions on one card.  The PCI specification allows for
      up to 8 functions (video, sound...) on a single card.

The PCI bus works with two different types of cards: 3.3 volt and 5
volt. These two different types of cards cannot be accidentally plugged
into the wrong slot, as the "keys" for the cards are on opposite ends of
the slot (most currently shipping motherboards have 5 volt connectors).
Of course the 3.3 volt and 5 volt cards won't work in the same slot,
with the single exception of cards which can operate with either voltage
(this is covered in the PCI spec).  An interesting trivia note is that
the connectors used for PCI cards are the same as those used for MCA.

The PCI bus is also limited to a maximum of four slots per bus (for
technical reasons); if more PCI slots are desired then a PCI - PCI
bridge must be used, in the same way that PCI is bridged to other buses
now.  Of those four slots, two must be able to accommodate a
busmastering device, and the busmaster-enabled slots must be labelled
somehow either on the board itself or in the manual for the board.

As a final note, not all PCI implementations are created equally.  Some
PCI chipsets, for instance, do not support an (optional) feature called
"byte merging", in which writes to sequential memory addresses are
merged into one PCI-to-memory operation.  (This will cause the bus to
have to actually wait for a 60 MHz Pentium CPU to catch up.)  Some
motherboards (like the Intel boards, for example) will also
automatically configure the PCI bus for you, eliminating the need to
fiddle with any jumpers of any kind.  (Others, like some of the oler
Asus boards, do not support this to my knowledge.)
------------------------------------------------------------------------

2) How does the PCI bus compare with:

   a) tbe ISA bus? (5/18/96)

      Right from the start, it should be apparent both that the PCI bus
      is not compatible with ISA (even the expansion slots for the two
      buses are different), and that technically PCI is much more
      advanced than ISA.  The ISA bus runs at a slower speed (8 MHz on
      most systems, though on many PCI/ISA systems with enhanced ISA
      timing the bus may be run at 10 or 11 MHz), does not allow for
      multiple busmasters (only one may be on the bus at any one time)
      and, because of the DMA controller it uses, will not allow
      peripherals which employ DMA to directly address memory above 16
      MB.  ISA will auto-configure (with the latest BIOSes installed),
      but will not share interrupts.  The ISA bus will support a maximum
      real-world data transfer rate of about 5 MB/sec (16 MB/sec is the
      theoretical maximum; burst transfer rates may approach about half
      of this), and uses a 16 bit data path.

      The ISA bus, in spite of its technical inferiority to PCI, still
      has a place in PC architecture, however; certainly you don't need
      PCI-type bandwidth for 16 bit/44.1 kHz digital audio, and serial
      ports are hardly taxing.  For that matter, neither are 900+ Kb/s
      CD-Rom and tape drives or ethernet 10Base-x.  However, use of
      these in combination with several other cards on the same (ISA)
      bus (video, disk I/O, etc.) will severely limit performance on
      most systems.

   b) The EISA bus? (5/18/96)

      The EISA bus is an attempt to extend ISA to a 32-bit bus which
      allows for proper busmastering.  While having the resulting
      advantage of compatibility with the large number of ISA-based
      cards in existence, this causes it to be slower than it could be,
      as it transfers 32 bits per clock cycle but runs at 8 MHz (for a
      theoretical maximum of 32 MB/sec).  The EISA bus also does not
      autoconfigure (I do not know if this has changed in the latest
      revisions as it has with ISA), though it is capable of sharing
      interrupts.  EISA never really caught on, and appears to be fading
      in popularity.

   c) tbe VL bus? (8/27/95)

      The VL bus was designed to overcome the speed limitations of the
      ISA bus.  It talks both directly to the CPU and the memory, and
      typically runs at the external clock rate of the CPU (up to a
      maximum of 40 MHz, though there are many boards which run at 50
      MHz, strictly a violation of the VL spec's).  As it is a 32-bit
      bus, the high speeds at which it runs can make for some very fast
      data transfers.

      The VL bus has its limitations, however.  For one, it truly is a
      "local bus", meaning that it talks directly to memory and to the
      CPU with no intervention from any bus arbitrators.  Because of
      this, th