4.  Definitions and Conventions

4.1 Definitions

For the purpose of this standard the following definitions apply:

4.1.1 ATA (AT Attachment):  ATA defines a compatible register set and a 40-pin 
connector and its associated signals. 

4.1.2 Data block: This term describes a data transfer, and is typically a 
single sector, except when declared otherwise by use of the Set Multiple 
command. 

4.1.3 DMA (Direct Memory Access): A means of data transfer between 
peripheral and host memory without processor intervention. 

4.1.4 Optional:  This term describes features which are not required by the 
standard. However, if any feature defined by the standard is implemented, it 
shall be done in the same way as defined by the standard. Describing a feature 
as optional in the text is done to assist the reader. If there is a conflict 
between text and tables on a feature described as optional, the table shall be 
accepted as being correct. 

4.1.5 PIO (Programmed Input/Output): A means of data transfer that requires 
the use of the host processor.

4.1.6 Reserved:  Where this term is used for bits, bytes, fields and code 
values; the bits, bytes, fields and code values are set aside for future 
standardization, and shall be zero.

..4.1.10 VU (Vendor Unique):  This term defines those features that can be 
..defined by the vendor in a specific implementation. Caution should be 
..exercised in defining and using such features since they may or may not 
..vary between vendors.
..
4.1.7 VU (Vendor Unique):  This term is used to describe bits, bytes, 
fields, code values and features which are not described in this standard, 
and may be used in a way that varies between vendors. 

4.2  Conventions

Certain terms used herein are the proper names of signals. These are printed 
in uppercase to avoid possible confusion with other uses of the same words; 
e.g., ATTENTION. Any lowercase uses of these words have the normal American-
English meaning. 

A number of conditions, commands, sequence parameters, events, English text, 
states or similar terms are printed with the first letter of each word in 
uppercase and the rest lowercase; e.g., In, Out, Request Status. Any lowercase 
uses of these words have the normal American-English meaning. 

The American convention of numbering is used i.e., the thousands and higher 
multiples are separated by a comma and a period is used as the decimal point. 
This is equivalent to the ISO convention of a space and comma. 

   American:          0.6                      ISO:          0,6
                  1,000                                  1 000 
              1,323,462.9                            1 323 462,9
 
