Consider a main memory system that consists of 8 memory modules attached to…
2014
Consider a main memory system that consists of 8 memory modules attached to the system bus, which is one word wide. When a write request is made, the bus is occupied for 100 nanoseconds (ns) by the data, address, and control signals. During the same 100 ns, and for 500 ns thereafter, the addressed memory module executes one cycle accepting and storing the data. The (internal) operation of different memory modules may overlap in time, but only one request can be on the bus at any time. The maximum number of stores (of one word each) that can be initiated in 1 millisecond is ____________.
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Correct answer: 10000
Answer: 10,000 stores can be initiated in 1 millisecond.
Explanation:
The bus is occupied for 100 ns per write request, and only one request may be on the bus at a time. Therefore a new store can be initiated at most once every 100 ns.
One millisecond equals 1,000,000 ns, so the maximum number of initiations is 1,000,000 ns ÷ 100 ns = 10,000.
Check module availability: each addressed memory module is busy for the 100 ns on the bus plus 500 ns thereafter, a total of 600 ns. To avoid addressing a still-busy module when starting stores every 100 ns, we need at least ceil(600/100) = 6 distinct modules. The system has 8 modules, so module contention does not reduce the initiation rate.
Therefore the bus limit governs, giving the final answer of 10,000 stores initiated in 1 millisecond.
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