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Enterprise-IV EISA VLB Motherboard User's Guide
5
Specifications,
Continued
Programmable Crystal Oscillator
The Enterprise-IV motherboard has a programmable crystal oscillator that supports all possible
motherboard frequencies.
Heat Sink for 50 and 66 MHz CPUs
The Enterprise-IV EISA Local Bus motherboard has a heat sink for all motherboards equipped with a 50
MHz 80486DX or 25 MHz (operates at 50 MHz internally) or 33 MHz (operates at 66 MHz internally)
80486DX2 to help dissipate heat. See page 91 for additional information about heat dissipation.
Processor Speeds
The Enterprise-IV operates at either of two speeds: high or low. High speed is set at time of manufacture to
the processor speed (25, 33, 50, or 66 MHz). A low speed that is approximately the same speed as an
original IBM® AT is simulated by adding extra cycles. The clock speeds can be changed via the <Ctrl>
<Alt> <+> and <Ctrl> <Alt> <-> keychords. These keychords can be changed by the OEM via AMIBCP.
System Memory
The Enterprise-IV EISA VLB motherboard supports up to 256 MB of onboard memory via four banks of
256 KB x 36, 1 MB x 36, 4 MB x 36, or 16 MB x 36 SIMMs. Each SIMM bank consists of four SIMM
slots, a total of 16 SIMM sockets. The 70 ns SIMMs must support fast page mode.