IBM JAGUAR V 386, Системное руководство

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GENERAL FEATURES
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MEMORY SYSTEM
Two banks of DRAMs can be installed on
motherboard and 256K, 1MB and 4MB DRAM SIMM
modules are supported. One bank of DRAM refers to four
pieces of SIMM modules. The maximum memory size is
32MB when using 4MB DRAM for all banks.
The DRAM controller supports Page mode.
Successive memory accesses within the same page need
not require wait state and thus CPU can run at full speed.
To enhance the system performance, shadow
RAM mode is supported. In shadow RAM mode, system
BIOS and video BIOS contained in low speed memory
such as EPROM and ROM are copied into DRAM.
Improvement is significant because access to DRAM is
much faster than ROM.
Hidden Refresh
In the original PC/AT design, the CPU suspends its
operation during memory refresh. The memory refresh
cycle takes about 5% of CPU time which is a short period
of time in a slow machine. Nevertheless, in a 33MHz
machine, it will significantly downgrade the system
performance since the CPU can complete more
operations in the same period.