2014/Thoughts06

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Computer Science 61 and E61
Systems Programming and Machine Organization

Lecture 6 thoughts

We think a lot in computer science about costs: time cost, space cost, memory efficiency. And these costs fundamentally shape the kinds of solutions we build. But you may not think as often about financial costs! These also fundamentally shape the systems we build—in some ways more fundamentally—and the costs of storage technologies have changed at least as dramatically as their capacities and speeds.

Costs per megabyte of storage technologies (constant 2010 dollars)

Year Memory Flash Hard disk
~1955 $411,000,000.00 $6,233.00
1970 $734,000.00 $260.00
1990 $148.20 $5.45
2003 $0.09 $0.305 $0.00132
2010 $0.019 $0.00244 $0.000073
~2013 $0.0047 $0.00078 $0.000038

Cost per byte relative to that of a hard disk in ~2013:

Year Memory Flash Hard disk
~1955 11,000,000,000,000 160,000,000
1970 19,000,000,000 6,800,000
1990 3,900,000 140,000
2003 2,400 8,000 35
2010 500 64 2
~2013 124 21 1

These are initial purchase costs & don’t include maintenance and power. DRAM uses more energy than hard disks, which use more than flash. (Prices from here and here. $1.00 in 1955 is $8.14 in 2010 dollars.)

Rough speeds of storage technologies

Type Latency Throughput
(sequential access)
Throughput
(random access)
Register 0.5ns
SRAM 4ns
DRAM 60ns
Flash (read) 30µs 250MB/s 140MB/s
Flash (write) 300µs 170MB/s 14MB/s
Hard disk ~4-9ms 58-96MB/s ~1MB/s

A typical recent disk might rotate at 15000 RPM. It would have ~4ms average seek time, ~2ms average rotational latency, and 58-96 MB/s maximum sustained transfer rate. (CS:APP2e)

To load 4 pages (that is, 4x4KB = 16KB) from disk takes ~8ms.