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IBM PC/XT Processor Speedup

IP.com Disclosure Number: IPCOM000062159D
Original Publication Date: 1986-Oct-01
Included in the Prior Art Database: 2005-Mar-09
Document File: 1 page(s) / 12K

Publishing Venue

IBM

Related People

Nolan, TJ: AUTHOR

Abstract

Since its introduction the IBM PC/XT has been limited to a clock speed of 4.77 MHz. This publication describes a method of increasing the processor speed. The IBM PC XT was designed with a 4.77 MHz processor clock. Since its introduction it has been considered impossible or impractical to increase the speed of the clock and thereby increase the performance of the system because: a) it would require massive and complicated changes to the motherboard and b) it would not support any products which reference the system clock. This method increases the processor clock speed with minimal change and maintains compatibility with most products which reference the system clock. Speeds as high as 7.4 MHz are possible depending on the speed rating of system memory (7.4 MHz requires 120 ns random- access memory).

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IBM PC/XT Processor Speedup

Since its introduction the IBM PC/XT has been limited to a clock speed of 4.77 MHz. This publication describes a method of increasing the processor speed. The IBM PC XT was designed with a 4.77 MHz processor clock. Since its introduction it has been considered impossible or impractical to increase the speed of the clock and thereby increase the performance of the system because:
a) it would require massive and complicated changes to the motherboard and b) it would not support any products which reference the system clock. This method increases the processor clock speed with minimal change and maintains compatibility with most products which reference the system clock. Speeds as high as 7.4 MHz are possible depending on the speed rating of system memory
(7.4 MHz requires 120 ns random- access memory). The clock speedup is achieved in the following manner. The original crystal is removed and replaced with a 22 MHz crystal (speeds between 14.31818 and 22 MHz are possible). Pin 12 on the system board clock generator (8284A) is cut, which disconnects the I/O bus system clock. The system clock is then supplied by a card which is inserted into any I/O slot including the XT short slot. This added card need only contain an 8284A clock generator running at the original speed of 14.31818 MHz. This clock is connected to pin B30 on the I/O bus, replacing the clock previously supplied by the motherboard clock generator. The clock supplied by this ad...