Binary Representation of Information

1. chapter8 Binary Representation of Information bit: 0 byte: 0110 11000 word: 01011100 11101111 00010000 11110000

2. How Big are Computer Memories? A single typewritten page of text:    ¶We the People of the United States, in Order to form a more perfect Union, establish Justice, insure domestic Tranquility, provide for the common defense, promote the general Welfare, and secure the Blessings of Liberty to ourselves and our Posterity, do ordain and establish this Constitution for the United States of America.

3. Measuring Memory Capacity 40 characters per line, 50 lines per page  40 * 50 = 2000 char/page = 2K char = 2K Bytes = 2 KB/page (eg) 1 book = 250 pages = 250 * 2 KB = 500 KB = 0.5 MegaByte  ½ MB = 1 book

4. Measuring Memory Capacity (eg) UO Library: 2,000,000 books 2,000,000 * ½ MB = 1,000,000 MB = 1,000 GB = 1 TB 1 UO Library = 1 TeraByte of digital storage

5. 110 Memory Metrics • 1 char (ASCII) = 1 Byte = 8 bits • 1 typed page = 2,000 Bytes = 2 KB • 1 book = 250 pages = 500,000 char = 500,000 Bytes = 500 KB = ½ MB • 1 UO Library = 2,000,000 books = 1,000,000 MB = 1,000 GB = 1 TB

6. Hard Disk Drives (HDD) Capacity and access speed In 2007, a typical enterprise, i.e. workstation HDD might store between 160 GB and 1 TB of data (as of July 2007), rotate at 7,200 or 10,000 RPM, and have a transfer rate of over 80 MB/sec. Laptop HDDs: In the 1990s, most spun at 4200 rpm. In 2007, a typical mobile HDD spins at 5400 rpm, with 7200 rpm models available for a slight price premium.

7. Hard Disk Drives (HDD) Exponential increases in disk space and data access speeds of HDDs have enabled consumer products that require large storage capacities TiVo personal video recorder  digital music playersIn addition, the availability of vast amounts of cheap storage has made viable a variety of web-based systems with extraordinary capacity requirements, such as the search and email systems offered by companies like Google.

8. HDDs Capacity measurements A disk specified by a disk manufacturer as a 30 GB disk might have its capacity reported by Windows 2000 both as "30,065,098,568 bytes" and "28.0 GB" The disk manufacturer used the SI definition of "giga", 109 to arrive at 30 GB; however, because the utilities provided by Windows define a gigabyte as 1,073,741,824 bytes (230 bytes, a gibibyte, or GiB), the operating system reports capacity of the disk drive as 28.0 GB.

9. HDD Failures The mean time to failure (MTBF): 0.5 to 1.5 million hours. MTBF research is conducted in laboratory environments A more valid metric is annualized failure rate (AFR). AFR is the percentage of real-world drive failures after shipping. (eg) Enterprise drives experience between .70%-.78% annual failure rates from the total installed drives

10. Misc 1 bit = 1 flip-flop. 1 Byte = 8 flip-flops. 1 Bps = 8 bps. 10 Mbps = 1.25 MBps. How many holes to fill the Albert Hall?

11. How Fast Are Computers? Data Transfer Rate: bps & Bps UOnet Data Transfer Rates (“phat pipes”): • Ethernet: 10 megabits/second (the speed of most UOnet connections). • fast Ethernet: 100 megabits/second (the speed at which many campus servers connect to UOnet). • gigabit Ethernet: 1000 megabits/second (1 Gbs; current speed of UOnet backbone).