RBBS in a Box Volume 1 #3.1/RBBSIABOX31.cdr/d86v/crystal.inf

Text File | 1986-01-05 | 13KB | 233 lines

Subject: Some Speedup info from Compuserve IBM PRO SIG
Date: Thu, 23 Jan 86 22:47:15 -0500
From: Dave Farber <[e-mail]>

                               January 22, 1986

This file was created in response to a request to make a reference guide for
speeding up the IBM PC-AT available in the CompuServe IBM SIG data libraries.
It contains information gathered from a number of IBM PC-AT users, companies,
and my own experiences.

When the PC-AT was released, the fact that IBM had chosen to socket the clock
crystal was greeted with much interest and speculation, and it's this ability
to remove the crystal that is the key factor in speeding up the AT. The crystal
is contained in a 1/2x3/8" silver housing that plugs into its socket located
near the 80286 chip, behind the center opening for the hard disk. The crystal
can be removed easily by inserting a small nonmagnetic screwdriver or table
knife between the crystal and socket, and pushing the crystal toward the AT's
red power switch, then lifting it up and out of the retaining clip. A faster
crystal can then be insterted to increase the operating speed of the 80286 CPU
chip which is driven at 1/2 the crystal speed. WARNING: Changing the crystal
may void the warranty so save the original crystal to reinstall if your system
needs servicing.

                          CRYSTAL SPEED-UP PRODUCTS

Crystals:
        The AT comes with a 12 mhz thick lead crystal, giving a 6 mhz CPU
        speed, but research done by ARIEL shows that (providing the new
        speed limiting ROM isn't installed) 99% of ATs will run with 16
        mhz, 85% with 18 mhz, and 68% with 20 mhz crystals. Two types of
        replacement crystals are available:
                1) Crystals with thin wire leads:
                   These crystals are very cheap and readily available, but
                   the lead wires are very thin, so may have to be bent double
                   to make good contact in the AT's crystal socket. These
                   crystals are better used for making speed switches, than
                   for use on the AT's motherboard. [ Herm Fischer discovered
           that the gold pins from an RS232 connector can be soldered
           to thin lead crystals providing a better fit. -wab]
                2) Crystals with thick leads:
           These crystals are more expensive, but properly fit the AT's
           crystal socket. ARIEL emphasizes the importance of using
           high quality, military grade thick lead crystals (which they
           sell) in the AT, and their claims may be valid as Peter
           Norton reported having problems with some cheap thin lead
           crystals which resolved when he switched to quality thick
           lead crystals, but I have used cheap thin lead crystals from
           B.G. Micro without problems, and found them to work well in
           homebrew speed switches.

Speed Switches:
        Some cases have been reported of software that won't install (probably
        due to the copy-protection) or run (due to certain types of timing
        loops) with the faster crystals installed, and speeded-up ATs will not
        work with some local area networks. To work around these problems, one
        can use a speed switch to switch back and forth between several speeds,
        using a slower speed for speed limited software ar LAN use, and faster
        speeds for number crunching, etc.. A homebrew speed switch can easily
        be made for < $10, using 2 crystals and a small DPDT switch connected
        to 2 wires that plug into the crystal socket (I have used one for
        months without problems), or a variety of commercial products are
        available, most of which consist of a switch and 2 to 5 crystals
        mounted on an expansion slot cover bracket (this prevents the slot from
        being used by any expansion boards) and connected to 2 wires plugged
        into the crystal socket.

                             VARIABLE OSCILLATORS

Another approach to increasing the AT's clock speed is to use a variable
oscillator instead of replacements crystals. BGI is currently offering such a
product.

                               FAST MEMORY CHIPS

When operating the AT at faster speeds, faster RAM chips may be required. In
some cases, faster RAMs are required on memory expansion boards, than on the AT
motherboard itself (This seems to be especially true of paged memory boards).
On the AT motherboard, 150ns chips generally work well at CPU speeds of 8 mhz,
and some users have found them adequate at CPU speeds as high as 10 mhz, though
one supplier of fast RAMs claimed that 150ns chips used in a 10 mhz AT would
get flaky from heat degeneration after 8 - 9 months of use. Basic guidelines
for motherboard RAMs would be for CPU speeds < 9mhz, use 150ns; for 9 - 10 mhz,
use 120ns; > 10 mhz, use 100ns. These same guidelines will also hold true for
some of the extended memory boards (such as the AST Advantage), but others may
require 120ns or 100ns only, or may not work at all at high speeds. The ability
of paged memory boards (such as the Rampage AT) to function at > 6mhz has been
erratic to date, and they may not work at all at high speeds, though the makers
of these boards are trying to solve these problems. In contrast, there have
been reports of AST Advantage boards working at CPU speeds of 12 mhz or
greater.

[I spoke with Chris Symes of Tall Tree. They use 150 ns chips exclusively.
Their memory boards run reliably at 18.7 Mhz. Tall Tree boards provide a memory
paging scheme which can be used to expand PC memory beyond 640K or the boards
can be used as straight AT memory bypassing the paging hardware. The paging
hardware does not slow access time.  They reccommend not using crystals faster
than 18Mhz and insist you should have no problems at this rate.

Crystals faster than 18 Mhz won't help on a standard AT anyway. The 80286 has a
few bytes of on board cache. Usually memory fetches will overlap with
computation. At speeds greater than 18 Mhz calculations proceed faster than the
AT can fetch memory. The processor will get memory bound and insert processor
wait states in order to wait for memory. Peter Norton's speed test will still
falsely show improvement as his loop of multiply divide pairs has a higher
ratio of compute-load per byte of instruction than most programs.  My
conclusion is that unless one designs an AT clone from scratch to run with a 20
Mhz crystal, don't try speeding up your AT past 18 Mhz -wab]

                                    802886s

Many, if not most ATs are shipped with 80286s rated at 6 mhz, and though they
usually work fine at 8 mhz, for those wanting to run the AT at 10 mhz or more,
the 80286-6 may have to be pulled from its socket and replaced with a faster
chip. There are 10, 12, 14, and 16 mhz 80286s available, though the supporting
chips may not be able to handle speeds > 12mhz. Reportedly, old ATs with the
orange motherboard may need to have some of the chips unsoldered and replaced
with faster chips before they can function at high speeds. AT users who want to
run at very high speeds can send their motherboard to BGI for any necessary
modifications and testing. It's believed that IBM will release a more expensive
8 mhz AT this year.

                                    80287s

In the AT, the 80287 math coprocessor is normally driven at 1/3 the crystal
speed, which is normally 4 mhz. The standard 4 mhz 80287s may not work with
crystals faster than 16 mhz. There are 8, 10, and 12 mhz 80287s available for
use in speeded-up ATs, though even with a 20 mhz crystal, the 80287 would be
driven at < 7 mhz, so for maximum speed, small boards are available that plug
into the 80287 socket and drive the 80287 at 8 mhz.

                                    80386s

Intel has been demonstrating an AT with a small board that holds an 80386 and
plugs into the 80286 socket, turning the AT into a limited 80386 machine.
Another company has a similar product but has chosen mot to market it. Several
companies have 80386 products for the AT in Beta test, so it's likely that
80386 products will be released this year for the AT, similar to the 80286
products already being sold for the PC and XT. BGI will be offering an 80386
motherboard for the AT, probably in March.

                                 NEC CPU CHIPS

It has been rumored for several months that NEC will be releasing another one
of their V series chips called the V-60, which will be a faster 80286 clone.
Dvorak reports that it will have a built-in math coprocessor. If they achieve
true 80286 compatibility, putting one in an AT with a fast crystal could be
interesting.

                               SOFTWARE PATCHES

Floppy Drive:
        Some AT users have experienced "Disk Read Error" type messages when
        accessing the floppy drive at CPU speeds > 8 mhz due to timeout errors.
        Patches are available to prevent this. A public domain version is
        available in the CompuServe IBM SIG data libraries, and several
        companies offer commercial versions that also speed-up the keyboard.

                                  NEW AT ROM:

The new AT ROM being installed in ATs having IBM's new 30 MB hard disk, has a
timing routine that prevents the system from operating at speeds > 6 mhz.
Currently, I know of only 4 ways users wanting to speed up these ATs can deal
with this problem:
        PROM Blasters: Use one to copy and/or patch a ROM.
        ROM Patch: Send your motherboard to BGI and get the ROM patched as part
                   of their motherboard upgrade package.
        PHOENIX ROM: Buy the Phoenix ROM for the AT and turn your AT into an
                     AT clone with the compatibility of a Compaq 286. (You
                     must use the Compaq GW BASIC).
        Circuit Boards: The AT-2 board from AMS defeats the ROM timing routine.
The best solution is to refuse to accept an AT with the new ROM from your
dealer, thus casting a vote with your buying power against what appears to be a
marketing move by IBM prior to the release of a faster, more expensive version
of the AT.

                           PRODUCTS AND SUPPLIERS

The product discriptions here consist of information supplied by the
manufacturer or distributor which is subject to change, so check with the
company for the latest info.

AMS (818-810-8443):
        High quality thick lead crystals
        AT-1 Board: Lets you switch manually between 3 speeds. Has a system
                    reboot button. Occupies an expansion slot.
        AT-2 Board: Same as AT-1, but lets you change speed from the keyboard
                    and defeats the timing routine in the new AT ROM.
ARIEL (201-788-2788):
        High quality thick lead crystals
        Fast 80286s
        Floppy drive timeout and keyboard speedup patches
        Beta testing 80386 product, and board to defeat the timing routine in
                the new AT ROM
BGI (215-538-3900):
        100ns RAMs
        80286s: 10, 12, 14, and 16 mhz
        80287s: 8, 10, and 12 mhz
        Variable Oscillator Board: Lets you select CPU speeds up to 12 mhz
                using DIP switches. Are working on a software driver to allow
                speed switching from the keyboard. Will hold an 80287 and drive
                it at up to 12 mhz.
        Fast RAM Board: Memory expansion up to 16 MBs with ports
        Fast AT Motherboard Upgrade: Send in your AT motherboard and they will
                fix it to enable operation at maximum speed.
        80386 Motherboard For AT: Uses a variable oscillator to drive current
                80386s at 14.5 mhz and future faster 80386s at 20 mhz CPU
        speed.
                Supposed to be available in March.
B.G. Micro (214-271-5546):
        Low cost crystals with thin wire leads for making your own speed
    switch.
Megahertz (801-355-8857):
        Speed Switches
        Fast Crystals
        8 mhz 80287 Board
        8 mhz 80287s
        PHOENIX ROM: For AT, to replace the new AT ROM with the timing routine.
        Floppy drive timeout and keyboard speedup patches
Microprocessors Unlimited (918-267-4961):
        100ns 256K RAMs
MicroWay (617-746-7341):
        8 mhz 80287 Board
        8 mhz 80287s
Ronsco Systems (312-534-1303):
        5-Speed Speed Switch

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

                                Stephen Sisler
                                  72366,3724