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Binary and Decimal Addressing

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Early computers used one of two addressing methods to access the system memory; binary (base-2) or decimal (base-10). The IBM 701 (1952) used binary and could address 2048 36-bit words. The IBM 702 (1953) used decimal and could address 10,000 7-bit words. One of the most successful early computers was the IBM 1401. It was introduced in 1959 and by 1961 one out every four electronic stored-program computers was an IBM 1401. It used decimal addressing and could have 1400, 2000, 4000, 8000, 12000 or 16000 characters of 8-bit core storage.[1] A reference to a "4k IBM 1401" meant 4000 characters of storage (memory).[2] The use of K in the binary sense as in a "32K store" can be found as early as 1960.[3]

By the mid 1960s binary addressing was the standard architecture in computer design. The computer system documentation would specify the memory size with an exact number such as 32,768, 65,536 or 131,072 words of storage. There were several methods used to abbreviate these quantities. Gene Amdahl's seminal 1964 article on IBM System/360 used 1K to mean 1024.[4] This style was used by other computer vendors, the CDC 7600 System Description (1968) made extensive use of K as 1024.[5] Another style was to truncate the last 3 digits and append K. The exact values 32,768, 65,536 and 131,072 would become 32K, 65K and 131K.[6] If 32,768 were rounded off it would be 33K. This style was used from about 1965 to 1975.

The use of the 1024 K was more common that the truncated K. Both were used, sometimes by the same company. The HP 21MX real-time computer (1974) denoted 196,608 as 196K and 1,048,576 as 1 M.[7] The HP 3000 business computer (1973) could have 64K, 96K, or 128K bytes of memory.[8]

The terms Kbit, Kbyte, Mbit and Mbyte started to be used as binary units in the early 1970s.[9] Most memory capacities were expressed in K. The IBM System/370 Model 158 brochure (1972) had the following: "Real storage capacity is available in 512K increments ranging from 512K to 2,048K bytes."[10] Megabyte was used to describe the 22-bit addressing of DEC PDP-11/70 (1975)[11] and gigabyte the 30-bit addressing DEC VAX11/780 (1977).

By the mid 1970s it was common to see K (or Kbyte) as 1024 and the occasional M (or MByte) as 1,048,576 for words or bytes of memory (RAM). K and M were also used with their decimal meaning for disk storage. The dual use of these prefixes as both decimal and binary was defined in early standards and dictionaries. The ANSI/IEEE Std 1084-1986[12] is still available for reference and defined kilo and mega. The term "computer storage" means system memory.[4]

"kilo (K). (1) A prefix indicating 1000. (2) In statements involving size of computer storage, a prefix indicating 210, or 1024."

"mega (M). (1) A prefix indicating one million. (2) In statements involving size of computer storage, a prefix indicating 220, or 1,048,576."

In the 1980s the terms kilobyte, megabyte, and gigabyte became popular along with the abbreviations KB, MB, and GB. The binary units Kbyte and Mbyte were formally defined in ANSI/IEEE Std 1212-1991.[13] The terms Kbyte, Mbyte, and Gbyte are found in the trade press and in IEEE journals.

Gigibyte was formally defined in IEEE Std 610.10-1994 as either 1,000,000,000 or 230 bytes.[14] Kilobyte, Kbyte, and KB are equivalent units and all are defined in current standard, IEEE 100-2000.[15]

The industry has coped with the dual definitions because system memory (RAM) typically uses the binary meaning while disk storage uses the decimal meaning. (There are exceptions especially with disks.) There are no SI units for computer storage capacity but the decimal meanings of KB, MB, and GB are often referred to as SI prefixes.

References

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  1. ^ IBM (April 1962). IBM 1401 Data Processing System: Reference Manual (PDF) (A24-1403-5 ed.). p. 9.
  2. ^ Sonquiest, John A. (December 1962). "Fixed-word-length arrays in variable-word-length computers". Communications of the ACM. 5 (12). ACM Press: 602. doi:10.1145/355580.369093. The following scheme for assigning storage for fixed-word-length arrays seems to meet these criteria and has been used successfully in working with linear arrays on a 4k IBM 1401.
  3. ^ Gruenberger, Fred (October 1960). "Letters to the Editor". Communications of the ACM. 3 (10). doi:10.1145/367415.367419. "The 8K core stores were getting fairly common in this country in 1954. The 32K store started mass production in 1956; it is the standard now for large machines and at least 200 machines of the size (or its equivalent in the character addressable machines) are in existence today (and at least 100 were in existence in mid-1959)." Note: The IBM 1401 was a character addressable computer.
  4. ^ a b Amdahl, Gene M. (1964). "Architecture of the IBM System/360" (PDF). IBM Journal of Research and Development. 8 (2). IBM: 87–101. doi:10.1147/rd.82.0087. {{cite journal}}: Unknown parameter |coauthors= ignored (|author= suggested) (help) Figure 1 gives storage (memory) capacity ranges of the various models in "Capacity 8 bit bytes, 1 K = 1024"
  5. ^ Control Data Corporation (November 1968). Control Data 7600 Computer System: Preliminary System Description (PDF). One type, designated as the small core memory (SCM) is a many bank coincident current type memory with a total of 64K words of 60 bit length (K=1024).
  6. ^ Control Data Corporation (1965–1967). Control Data 6400/6500/6600 Computer Systems Reference Manual (Pub No. 60100000 ed.). pp. pg 2-1. Central Memory is organized into 32K, 65K, or 131K words (60-bit) in 8, 16, or 32 banks of 4096 words each. {{cite book}}: |pages= has extra text (help)
  7. ^ Frankenberg, Robert (October 1974). "All Semiconductor Memory Selected for New Minicomputer Series" (PDF). Hewlett-Packard Journal. 26 (2). Hewlett-Packard: pg 15-20. Retrieved 2007-06-18. 196K-word memory size {{cite journal}}: |pages= has extra text (help)
  8. ^ Hewlett-Packard (November 1973), "HP 3000 Configuration Guide" (PDF), HP 3000 Computer System and Subsystem Data: 59
  9. ^ Lin, Yeong (September 1972). "Cost-performance evaluation of memory hierarchies". Magnetics, IEEE Transactions on. 8 (3). IEEE: pg 390-392. doi:10.1109/TMAG.1972.1067329. Also, random access devices are advantageous over serial access devices for backing store applications only when the memory capacity is less than 1 Mbyte. For capacities of 4 Mbyte and 16 Mbyte serial access stores with shift register lengths of 256 bit and 1024 bit, respectively, look favorable. {{cite journal}}: |pages= has extra text (help); Unknown parameter |coauthors= ignored (|author= suggested) (help)
  10. ^ IBM (1972). "System/370 Model 158 brochure" (PDF). IBM. All-monolithic storage ... (1024-bit NMOS) This new improvement of processor storage makes system expansion more economical. Real storage capacity is available in 512K increments ranging from 512K to 2,048K bytes. {{cite journal}}: Cite journal requires |journal= (help)
  11. ^ Bell, Gordon (November 1975). "Computer structures: What have we learned from the PDP-11?" (PDF). ISCA '76: Proceedings of the 3rd Annual Symposium on Computer Architecture. ACM Press: pg 1-14. memory size (8k bytes to 4 megabytes). {{cite journal}}: |pages= has extra text (help); Unknown parameter |coauthors= ignored (|author= suggested) (help)
  12. ^ ANSI/IEEE Std 1084-1986 IEEE Standard Glossary of Mathematics of Computing Terminology. October 30, 1986. doi:10.1109/IEEESTD.1986.79649. ISBN 0-7381-4541-6. kilo (K). (1) A prefix indicating 1000. (2) In statements involving size of computer storage, a prefix indicating 210, or 1024. mega (M). (1) A prefix indicating one million. (2) In statements involving size of computer storage, a prefix indicating 220, or 1,048,576.
  13. ^ ANSI/IEEE Std 1212-1991 IEEE Standard Control and Status Register (CSR) Architecture for Microcomputer Buses. July 22, 1992. doi:10.1109/IEEESTD.1992.106981. ISBN 0-7381-4336-7. Kbyte. Kilobyte. Indicates 210 bytes. Mbyte. Megabyte. Indicates 220bytes. Gbyte is used in the Foreword.
  14. ^ IEEE Std 610.10-1994 IEEE Standard Glossary of Computer Hardware Terminology. June 24, 1994. doi:10.1109/IEEESTD.1995.79522. ISBN 1-55937-492-6. gigabyte (gig, GB). This term may mean either a) 1,000,000,000 bytes or b) 230 bytes. … As used in this document, the terms kilobyte (kB) means 210 or 1024 bytes, megabyte (MB) means 1024 kilobytes, and gigabyte (GB) means 1024 megabytes.
  15. ^ Institute of Electrical and Electronics Engineers (2000). The Authoritative Dictionary of IEEE Standards Terms. IEEE Computer Society Press. doi:10.1109/IEEESTD.2000.322230. ISBN 0-7381-2601-2. "kB See kilobyte." "Kbyte Kilobyte. Indicates 210 bytes." "Kilobyte Either 1000 or 210 or 1024 bytes." The standard also defines megabyte and gigabyte. There is a note that an alternative notation for base-2 is under development.

Leave comments here

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I don't think the evidence yet supports the statement that by the mid-1970's it was "common to see ... M (or MByte) as 1,048,576 for words or bytes of memory (RAM)". Yr 1972 find is a great one, but it is only one point. A counter point is the Nov 1983 Byte magazine which in 720 pages has only one page (631) advertising both a "2MB" LSI11 memory (binary) and a "140MB" HDD (decimal) but 17 other pages with MB only in a decimal sense. If it was uncommon in 1983 how can it be common in the mid-1970's. I'm busy with a C# problem right now so I don't have time to research much, but sometime this week I will look at a late 1970's Datamation and Byte Magazine to see what I find. Other interesting journals might be MiniMicro or some DEC publication but I don't have access to early editions of them.

What do you think the criteria should be for the use of common?

For example, IMHO, the DiskTrend use in 1977 was necessary for decimal M, given it was the leading and a widely circulated analysis of the HDD industry, but it required other supporting evidence such as listed in the timeline to say M was common in a decimal sense.

My guess is M (binary) did not become common until we saw PC's with significantly more memory than 1 MiB :-) Tom94022 17:26, 18 June 2007 (UTC)


Floppy Disks

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Floppy disk drive and media manufacturers use decimal units for unformatted recording capacity while most computer operating systems use binary units to measure the formatted capacity. The original IBM Personal Computer (1981) used a Tandon TM100 5 1/4 inch floppy disk drive. The single sided drive was rated at 250 kilobytes (unformatted) and the double sided version was rated at 500 kilobytes. [1]

A 5 1/4 diskette recorded at double density MFM will hold 6250 bytes per track and 40 tracks per side yield 250,000 bytes per side. To make it practical to record smaller blocks of data, the tracks are formatted into sectors with gaps between them. The gaps allow individual sectors to be recorded without overwriting adjacent sectors. Each sector also has additional header bytes to identify the sector.

With IBM PC-DOS 1.0 and 1.1, each track has 8 sectors of 512 bytes and this provides 163840 bytes per side (8 x 512 x 40). The IBM user documentation referred to this as "160KB" for single sided diskette and "320KB" for double sided diskette. Starting with PC DOS 2.0 (1983), each track had 9 sectors of 512 bytes. The formatted capacity was increased to 184320 bytes per side or 368640 bytes per diskette. The IBM documentation referred to these as "180KB" and "360KB" diskettes. The same drives and media can have different capacities depending on format.[2]

On all diskettes the capacity available to the user will be smaller that the total number of sectors because some are reserved by the operating system for boot records or directory tables.

The IBM Personal Computer/AT (1984) had a new 5 1/4 inch disk drive that had 80 tracks per side, rotated at 360 rpm (versus 300 rpm) and had a new diskette media. The formatted capacity was 1,228,800 bytes or 1200 KB. (80 tracks x 15 sectors x 512 bytes x 2 sides)

The IBM PC Convertible (1986) used the 3 1/2 inch diskettes. These were similar in recording technology to the original 5 1/4 inch drives except they had 80 tracks per side. The formatted capacity was 737,280 bytes or 720 KB. Apple used the same disk with a different recording technology, GRC, that gave a formatted capacity of 819,200 bytes. Apple referred to this as an 800K disk. [1]

The last widely adopted diskette was the 3 1/2 inch high density. This has twice the capacity as the 720 KB diskettes, 1,474,560 bytes or 1440 KB. The drive was marketed as 1.44 MB when a more accurate value would have been 1.4 MB (1.40625 MB). Some users have noticed the missing 0.04 MB.[2] The 1200 KB 5 1/2 inch diskette was marketed as 1.2 MB (1.171875 MB) without any controversy.

The Flash Memory Drive is replacing the floppy disk and many new computers come without a floppy disk drive.

  1. ^ Tandon (Janurary1984). TM100-1, TM100-2 Flexible Disk Drives: Product Specification and User's Manual (PDF). Tandon Corporation. pp. pg 2-4. {{cite book}}: |pages= has extra text (help); Check date values in: |date= (help)
  2. ^ IBM (January 1983). Disk Operating System by Microsoft (Version 2.0). IBM Corporation. pp. A-2. "Beginning with DOS Version 2.00, DOS formats diskettes at 9 sectors per track, which increases capacity from 163840 to 184320 characters of information for single-sided diskettes and from 327680 to 368640 characters for dual-sided diskettes. The smaller capacity diskettes created by DOS Version 1.00 or DOS Version 1.10 (8 sectors per track) are also usable with DOS Version 2.00."
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