PC-AT High Performance Slowdown
By David Keil
AT-SLOW is a utility which when loaded will use the high
resolution timer found in a PC-AT or close clone to slowdown
games and other programs which run to fast on PC-AT's.
This program is hardware dependent and requires a PC-AT or
close clone and a 80286/80386 processor to operate. AT-SLOW uses
the AT's real time clock found at interrupt 70h to slowdown the
Using the real time clock's interrupt has two advantages
over the usual use of the normal PC's timer.
1 - The high resolution timer can occur up to 8096 times a second
(as opposed to 18.2 with the normal timer). This provides a much
smoother slowdown than with the normal timer. This also
provides a higher degree of performance reduction.
2 - Since this slowdown uses interrupt 70h and only AT's use
this interrupt, programs don't know to re-vector it. So
programs that don't work with mormal slowdown programs
will work with AT-SLOW.
The command for using AT-SLOW is
/t = ??? is amount to slowdown PC-AT. Valid range is 0-999.
/h = Show this help screen.
/f = Fix value for high speed machines. Valid range is 1-9.
Use when AT-SLOW does not seem to work or is disabled by
higher speed machines. Default value is 1.
/? = Show current program settings.
+ = Enable option.
- = Disable option.
The range of values for delay is 1-999. Values of 20-60
on 286 machines is usually adequate. As the delay value is increased
there will come a point when the computer actually begins to speed
back up. This is because there is to much delay for the computer to
service all the interrupts being generated so the total delay is
actually decreased. When this happens reduce the delay value slowly
until there is a sudden decrease in performance.
Once installed AT-SLOW can be disabled by using the /t- option
and can be re-enabled using the /t+ option or by changing the delay
value. The /t- option will disable the timer interrupt and return
the computer to normal speed (entering /t0 will eliminate the delay
but will not disable the interrupt). AT-SLOW should not be removed
or disabled using memory management programs as the interrupt may
remain active and this will cause about a 20 to 50 percent reduction in
performance. The program uses very little memory however and when
disabled does not effect performance so leaving it in memory should
not be of great concern.
A couple of major enhancements have been made since the last
version of AT-SLOW.
1) The AT's real time clock has been speeded up to give a smooth delay
right down to the same speed as a 4.77mhz PC. Even on 386 machines
that require higher delay values.
2) Before if too large of a delay value was entered the computer would
slowdown to a point of being useless or would lockup completely.
Now if too large a delay value is entered the computer will actually
speed back up.
This program is provided AS IS without any warranty, expressed
or implied, including but not limited to fitness for a particular
If you find AT-SLOW useful:
This program is copyrighted and may only be distributed
in unmodified form and with this DOC file included.
A lot of time and effort went into the finding of information
and writing of AT-SLOW. So if you find this program useful (and I'm
sure you will) and would like to support the development of more PC-AT
(and other high performance computers) related software.
Please fill out the registration form on the following page and send it
along with the registration fee to:
David Keil / Better Software Co.
10 W. Wilburn Ave.
Greenville, S.C. 29611
======================= IMPORTANT ANNOUNCEMENT ===========================
* * * The registered version of AT-SLOW has had new options added... * * *
These options include:
1) Hot-key changing and disabling of slowdown value.
2) Hot-key exit to DOS that works with ANY! program.
3) Hot-keys ARE NOT DISABLED by other programs.
4) Option to remove delay program from memory.
5) Eliminate 'Push any key to continue' prompt, and many more.
========================== A T T E N T I O N ===========================
The hot-key to DOS option we believe to be the most important
development in PC compatible software in recent years. To our knowledge
there is no other program that can make the following claim.
With this option a user can exit ANY program at ANY time they want
(not recommended during disk access), even if the computer is locked up
(if CTRL-ALT-DEL will work so will hot-key to DOS although is is not
No more re-booting after your favorite game that won't exit back to DOS
(some games may not leave the computer in a usable condition). No more
re-booting your computer just because you executed a program you didn't
mean to. That little extra protection in this age of computer viruses.
So don't wait register today so you can make full use of the power
of your AT machine.
Please support quality shareware by registering it.
We thank you for your support.
AT-SLOW PAID Registration form
Remit To: David Keil / Better Software Co.
10 W. Wilburn Ave.
Greenville, SC 29611
Voice (803) 295-4971
Data (803) 269-7899
____ AT-SLOW Registration $10.00
____ Update on 5.25 inch disk plus shipping & handling $ 2.50
____ Update on 3.25 inch disk plus shipping & handling $ 5.00
____ Update to be downloaded off BBS (Save shipping charges) $ 0.00
Total amount enclosed $_______
Payment by check or money order (U.S. bank or branch)
..... Following needed for 3 month free membership on Hackers Paradise
Work Phone _____ __________ Home Phone _____ __________
The following will be your user ID:
First Name _____________
Last Name _____________
An account will be setup for you within 24 after receiving your
registration (10 days for personal check). Mail will be left for you which
will tell you how to download your upgrade. Registered users will be notified
on the BBS of upgrades in AT-SLOW.
..... Following needed for shipment of upgrade.