Today's 2007 Memory Hierarchy Frequency Latency Relative System Component Latency 1 Hz 1 sec 6 Hz 150 milliseconds Average DVD/CD-ROM/Floppy Disk seek latency 100 Hz 10 milliseconds Average hard disk seek latency (15 times faster than DVD) 1 KHz 1 millisecond 13 KHz 77 microseconds Non-volatile flash memory (USB Pen Drives 130 times faster than Hard Disks) 390 KHz 2.56 microseconds Samsung non-volatile phase-change RAM (PRAM) due in 2008 (30 times faster than flash) 1 MHz 1 microsecond 6.5 MHz 154 nanoseconds IBM/Macronix/Qimonda non-volatile phase-change RAM (PRAM) due in 2015 (500 times faster than flash) http://en.wikipedia.org/wiki/Phase-change_RAM 8.3 MHz 120 nanoseconds Total cycle time for inexpensive SDRAM (83,000 times faster than Hard Disks) 25 MHz 40 nanoseconds Total cycle time for expensive SDRAM (250,000 times faster than Hard Disks) 200 MHz 5 nanoseconds DDR 400 Front Side Bus (FSB) speed 266 MHz 3.76 nanoseconds Fast Front Side Bus (FSB) speed 333 MHz 3.33 nanoseconds 400 MHz 2.5 nanoseconds Typical DDR DRAM access latency 500 MHz 2 nanoseconds Fastest Front Side Bus (FSB) speed 800 MHz 1.25 nanoseconds Fast (quad-pumped) DRAM 1 GHz 1 nanosecond Total cycle time of on-chip L1 cache memory 2 GHz 500 picoseconds Typical CPU Speed 3 GHz 333 picoseconds Fast CPU 6 GHz 150 picoseconds ---------------- Assuming a conservative three clock cycles per instruction (CPI): 2 GHz CPU = 3 X 500 picoseconds = 1.5ns = 666 Million instructions per second (MIPS) 666 MIPS CPU matches the L1 cache DRAM (Intel Core 2 Duo with 4 MiB of on-chip L1 cache) 666 MIPS CPU is 27 times faster than high speed 25 MHz DRAM 666 MIPS CPU is 80 times faster than 8.3 MHz DRAM 666 MIPS CPU is 51,000 times faster than 13 KHz Flash memory 666 MIPS CPU is 6,666,667 times faster than 100 Hz Hard Disk If the CPU ran at 1 Hz: Cook-in-the-Kitchen Analogy: 3 secs to access cache memory Fetch an item from the kitchen cabinet. Typical CPU is 60 times faster than typical memory Takes a minute to access main memory Go out the garage for an item. Typical CPU is 6.67 million times faster than a hard disk. 77 days to access a hard disk Drive around the world 325 miles/day X 77 = ~25,000. Assuming a more realistic 1.5 clock cycles per instruction (CPI): 2 GHz CPU = 1.5 X 500 picoseconds = 750 picoseconds = 1.33 billion instructions per second (BIPS) 1.3 BIPS CPU is 2 times faster than L1 cache DRAM (Intel Core 2 Duo with 4 MiB of on-chip L1 cache) 1.3 BIPS CPU is 54 times faster than 25 MHz DRAM 1.3 BIPS CPU is 160 times faster than 8.3 MHz DRAM 1.3 BIPS CPU is 102,000 times faster than 13 KHz Flash memory 1.3 BIPS CPU is 13,333,333 times faster than 100 Hz Hard Disk If the CPU ran at 1 Hz: Cook-in-the-Kitchen Analogy: 6 secs to access cache memory Fetch an item from the refrigerator. Typical CPU is 120 million times faster than typical memory Two minutes to access main memory Go to the neighbor's house to get an item. Typical CPU is 13.33 million times faster than a hard disk. Half a year (154 days) to access a hard disk Two trips around the world @ 325 miles/day. ---------------- Fast (40 ns) memory is 250,000 times faster than a 10 ms hard disk. Fast (40 ns) memory is 2,000 times faster than a 77 microsecond flash drive. 77 microsecond flash drive is 130 times faster than a 10 ms hard disk. --------------- Disk seek latency is different from sequential sector transfer rate. Single disk (non-RAID) sequential transfer rates vary from a low of 12 MiB/s to a maximum of 50 MiB/s. However, due to seek latency, radom block I/O may only yield a 3 MiB/s transfer rate.