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Critical Points on Personal Computer Basics. DRAM vs. SRAM. Number of transistors/cell DRAM: 1 SRAM: 4 Expense Ratio 1:4 DRAM Refresh Interval: 3.86 msec = 3,860 μsec = 3,860,000 nsec DRAM cycle time (typical) = 60 nsec (read/write time) # of cycles/refresh = (3,860,000/60) - 64,333.
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DRAM vs. SRAM • Number of transistors/cell • DRAM: 1 • SRAM: 4 • Expense Ratio 1:4 • DRAM Refresh Interval: 3.86 msec = 3,860 μsec = 3,860,000 nsec • DRAM cycle time (typical) = 60 nsec (read/write time) • # of cycles/refresh = (3,860,000/60) - 64,333
Interrupt,Exception, Trap • Interrupt: raised by a hardware device • Exception: raised by the CPU • Trap: raised by software • All are referred to generically as interrupts. • Handled via: • Interrupt Vector Table (old): 4 Bytes/entry • I/O Address Table or Interrupt Descriptor Table: 8 Bytes/entry