The Bit Budget Begriff

  All computer storage is finite.  *

  1. FIXED BIT BUDGETS:

Understanding the bit allocation in software or hardware as a bit budget: with a bit budget of n bits, any one of 2n different values can be stored (range from 0 through 2n-1). In other words, n bits makes 2n unique different addresses possible.

Note that all computer storage is finite!*

There will be a maximum size (extent) for any storage requested. All bit values are shown – Here is a storage space (or data communications protocol field) with a bit budget of 8:

overflow

0

0

1

0

1

1

0

1

truncation

 

high-order bit, most significant bit

 

 

 

 

 

 

low-order bit,
least significant bit

 

2.      BIT BUDGETS AND LARGEST NUMBERS/HIGHEST ADDRESSES:

·        How many different numbers (addresses, bit patterns, or bit combinations) can be stored with a bit budget of… ?
2, 3, 4, 5, 6, 7, 8, 16, 32, 64, or 128 bits

·        What is the largest number or highest address (hint: 1 less than number of different bit combinations based on bit budget allocation) that can be stored with this bit budget?
2, 3, 4, 5, 6, 7, 8, 16, 32, 64, or 128 bits:

3.      ESTABLISHED BIT BUDGETS for PARTICULAR (standardized or proprietary) TECHNOLOGIES:

What are the bit budgets for… ?

o       an ASCII byte

o       an EBCDIC byte

o       a UCS/Unicode character

o       an octet

o       Bluetooth “active slave” address (INFS3230, INFS6230)

o       MAC address OUI octets (Organization Unique Identifier)

o       Ethernet address

o       Port Number (UDP or TCP, Internet)

o       an IPv4 address

o       an IPv6 address

o       registers in Burd Ch. 4 (INFS2210, INFS6210)

o       IEEE 802.1Q VLAN identification tag for frame (INFS4410, INFS6230)

o       IEEE 802.1p bits in IEEE 801.1Q header to assign Class of Service (CoS) (INFS4410, INFS6230)

o       Differential Services Code Point (DSCP) prioritization using bits from IP header Type of Service (ToS) octet (INFS4410, INFS6230)

o       “Kind of Option” field in TCP header options (INFS6230) What is the maximum number of options supported?

o       “Maximum Segment Size” length field in TCP header MSS option (INFS6230) What is the highest maximum segment size supported?

Example:

o       CSMA/CD Extreme Networks – see Stephen Haddock at http://grouper.ieee.org/groups/802/3/z/public/presentations/sep1996/SHbitbud.txt

 

4.      VARIABLE or CALCULATED BIT BUDGETS for PRACTICAL APPLICATIONS:

 

o       DVDs – see Joe Clark on “Bit Budget Myths,” at http://www.joeclark.org/access/dvd/finer-points.html#bitbudgetmyths – examples of DVD bit budgets are provided, definition of bit budget for DVD applications is given

o       See also a bit budget calculator for DVDs at http://www.customflix.com/Special/AuthoringNightmares/03/BitBudget.jsp (CustomFlix)

5.      BIT BUDGETS and HEX REPRESENTATION:

Note that with a bit budget of 4 bits you can store 4-bit numbers in each hex digit location. You can then represent each number (4-bit address) with a single hex digit (ratio 4 bits to 1 hex digit or 4:1).

6

0

1

1

0

Example for 8 bits (2 hex digits) – 2D16 = 001011012:

2

D

0

0

1

0

1

1

0

1

o       How many hex digits does it take to represent a binary number stored according to a bit budget of… ?
4, 16, 32, 64, or 128 bits

* in today’s dominant computer technologies.

Contact: Valerie J. Harvey, RT(R), PhD, C&IS, RMU
As of: 2008-10-25
Copyright 1998-2005 by RMU