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what is a far pointer
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Answer Posted / imran hassan bergi
Near pointers have a size of 2 bytes. They only store the
offset of the address the pointer is referencing. An
address consisting of only an offset has a range of 0 - 64K
bytes starting from the beginning of DGROUP. A near pointer
can be incremented and decremented using arithmetic
operators (+, -, ++, and --) through the entire address
range. Any attempt to increment a near pointer that has a
value of 64K (0xffff) will result in a value of 0. This is
referred to as wrapping the pointer. A corresponding result
can be expected when attempting to decrement a pointer that
contains an address of 0, except the result will be 64K
instead of 0. In addition to being incremented and
decremented, near pointers can be compared to one another
using relational operators ( <, >, ==, >= and <= ). Far
pointers have a size of 4 bytes. They store both the
segment and the offset of the address the pointer is
referencing. A far pointer has an address range of 0 - 1M
bytes. It is important to understand that an addressing
range of 1M does not remove the 640K barrier from the
program. It means that the pointer can address the upper
memory area (641 - 1M) which typically contains video
memory, ROM and anything else that may be loaded high. A
far pointer can be incremented and decremented using
arithmetic operators. When a far pointer is incremented or
decremented ONLY the offset of the pointer is actually
incremented or decremented. The segment is never
incremented by the arithmetic operators. This means that
although a far pointer can address up to 1Mb of memory, it
can only be incremented through 64Kb and the offset will
start at zero again without changing the value of the
segment. This is referred to as "wrapping" the pointer
(e.g. 0F3E:FFFF + 1 = 0F3E:0000). When a far pointer is
decremented from zero it will wrap the other way and become
64K. Far pointers are not unique. It is possible to have
two far memory addresses that have different segments
values and different offset values that address the same
memory location e.g. 0777:2222 has an absolute address of
07770 + 2222 = 09992 and 0999:0002 has an absolute address
of 09990 + 0002 = 09992. When relational operators are used
on far pointers only the offsets are compared. For example:
if we let a = 0777:2222 and let b = 0999:0002 then a == b
would return false because this is equivalent to 2222 ==
0002 which is in fact false. In other words relational
operators will only work on far pointers if the segment
values of the pointers being compared are the same. Huge
pointers have a size of 4 bytes. They store both the
segment and the offset of the address the pointer is
referencing. A huge pointer has an address range of 0 - 1M
bytes. A huge pointer can be incremented and decremented
using arithmetic operators. The only difference between a
far pointer and a huge pointer is that a huge pointer is
normalized by the compiler. A normalized pointer is one
that has as much of the address as possible in the segment,
meaning that the offset is never larger than 15. A huge
pointer is normalized only when pointer arithmetic is
performed on it. It is not normalized when an assignment is
made. You can cause it to be normalized without changing
the value by incrementing and then decrementing it. The
offset must be less than 16 because the segment can
represent any value greater than or equal to 16 (e.g.
Absolute address 0x17 in a normalized form would be
0001:0001. While a far pointer could address the absolute
address 0x17 with 0000:0017, this is not a valid huge
(normalized) pointer because the offset is greater than
0000F.). Huge pointers can also be incremented and
decremented using arithmetic operators, but since they are
normalized they will not wrap like far pointers. Huge
pointers can be reliably used with relational operators
because they are normalized. This works because
normalization of huge pointers insures that every huge
pointer is unique. It is important to understand that huge
pointers are never the default pointer, even in the huge
memory model.
| Is This Answer Correct ? | 27 Yes | 5 No |
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The rich analysts of Fernand Braudel arid his fellow Annales historians have made significant contributions to historical theory and research. In a departure from traditional historical approaches, the Annales historians assume (as do Marxists) that history cannot be limited to a simple recounting of conscious human actions, but must be understood in the context of forces and material conditions that underlie human behavior. Braudel was the first Annales historian to gain widespread support for the idea that history should synthesize data from various social sciences, especially economics, in order to provide a broader view of human societies over time (although Febvre and Bloch, founders of the Annales school, had originated this approach). Braudel conceived of history as the dynamic interaction of three temporalities. The first of these, the evenmentielle, involved short-lived dramatic events such as battles, revolutions, and the actions of great men, which had preoccupied traditional historians like Carlyle. Conjonctures was Braudel’s term for larger cyclical processes that might last up to half a century. The longue duree, a historical wave of great length, was for Braudel the most fascinating of the three temporalities. Here he focused on those aspects of everyday life that might remain relatively unchanged for centuries. What people ate, what they wore, their means and routes of travel—for Braudel these things create “structures’ that define the limits of potential social change for hundreds of years at a time. Braudel’s concept of the longue duree extended the perspective of historical space as well as time. Until the Annales school, historians had taken the juridical political unit—the nation-state, duchy, or whatever—as their starting point. Yet, when such enormous timespans are considered, geographical features may well have more significance for human populations than national borders, In his doctoral thesis, a seminal work on the Mediterranean during the reign of Philip II, Braudel treated the geohistory of the entire region as a “structure” that had exerted myriad influences on human lifeways since the first settlements on the shores of the Mediterranean Sea. And so the reader is given such arcane information as the list of products that came to Spanish shores from North Africa, the seasonal routes followed by Mediterranean sheep and their shepherds, and the cities where the best ship timber could be bought. Braudel has been faulted for the imprecision of his approach. With his Rabelaisian delight in concrete detail, Braudel vastly extended the realm of relevant phenomena but this very achievement made it difficult to delimit the boundaries of observation, a task necessary to beginning any social investigation. Further, Braudel and other Annales historians minimize the differences among the social sciences. Nevertheless, the many similarly designed studies aimed at both professional and popular audiences indicate that Braudel asked significant questions that traditional historians had overlooked. 14) The primary purpose of the passage is to: a) show how Braudel’s work changed the conception of Mediterranean life held by previous historians. b) evaluate Braudel’s criticisms of traditional and Marxist historiography. c) contrast the perspective of the longue duree with the actions of major historical figures d) outline some of Braudel’s influential conceptions and distinguish them from conventional approaches. 15) The author refers to the work of Febvre and Bloch in order to: a) illustrate the limitations of the Annale tradition of historical interpretation. b) suggest the relevance of economics to historical investigation. c) debate the need for combining various sociological approaches. d) show that previous Annales historians anticipated Braudel’s focus on economics. 16) According to the passage, all of the following are aspects of Braudel’s approach to history EXCEPT that he: a) attempted to draw on various social sciences. b) studied social and economic activities that occurred across national boundaries. c) pointed out the link between increased economic activity and the rise of nationalism. d) examined seemingly unexciting aspects of everyday life. 17) In the third paragraph, the author is primarily concerned with discussing: a) Braudel’s fascination with obscure facts. b) Braudel’s depiction of the role of geography in human history. c) the geography of the Mediterranean region. d) the irrelevance of national borders. 18) The passage suggests that, compared with traditional historians, Annales/i> historians are: a) more interested in other social sciences than in history. b) critical of the achievements of famous historical figures. c) skeptical of the validity of most economic research. d) more interested in the underlying context of human behavior. 19) Which of the Following statements would be most likely to follow the last sentence of the passage? a) Few such studies however, have been written by trained economists. b) It is time, perhaps, for a revival of the Carlylean emphasis on personalities. c) Many historians believe that Braudel’s conception of three distinct “temporalities” is an oversimplification. d) Such diverse works as Gascon’s study of Lyon and Barbara Tuchman’s A Distant Mirror testify to his relevance. 20) The author is critical of Braudel’s perspective for which of the Following reasons a) It seeks structures that underlie all forms of social activity. b) It assumes a greater similarity among the social sciences than actually exists. c) It fails to consider the relationship between short-term events and long-term social activity. d) It rigidly defines boundaries for social analysis.
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