Complete Extensive Summary Cos2621

Note: This summary consists out of 3 sections. Theory, Application
and Coding.


Theory section:
Note: Not all the theory is covered, because there are too much theory and
normally not a lot of theory is covered in the exams. Only the most frequent
asked exams questions are covered in the theory. Exams are much more
practical than theory based.

Memory hierarchy




Memory accessing methods
 Sequential access method: Data access is done sequentially (i.e. in a linear
sequence), such as on magnetic tape. Data access is very slow. E.g. magnetic tape.

,  Direct access method: Data is accessed by going directly to where it is physically
located on the device. Data access is relatively quickly. E.g. Hard disk.
 Random Access method:
Each addressable location in memory has a unique, physically wired-in addressing
mechanism. The time to access a given location is independent of the sequence of
prior accesses and is constant. Thus, any location can be selected at random and
directly addressed and accessed. Data access is fast, faster than direct. E.g. RAM.
 Associative Access Method: Access Data conducted by "compare", which compares
the "content" of the data sought by the "key" of his, not based on address data. Data
access is very fast. E.g. Cache Memory.




Optical Memory (Optical Disk Products) p217
CD, CD-ROM, DR-R, DVD, DVD-R, DVD-RW, Blu-ray DVD




Blu-Ray DVD: 3 versions available BD-ROM, BD-R and BD-RE.



NASM AND DEBUG
NASM is an assembler
DEBUG is a utility to assemble and debug programs.

,NASM assumed numbers to be decimals and DEBUG assumes numbers as
hexadecimal value.



Flip-Flops
 The simplest form of sequential circuit.
 All Flip flops share the following properties:
- It is a bistable device. It exists in one of two states and, in the
absence on input, remains in that state.
- It has two output, which are always complements of each other.
These are labelled


ASCII p421
 Each character represented by 7-bit pattern, but stored using 8 bits per character.
 The last bit (eight bit) may be set to 0 or used as parity bit for error detection.
 128 different characters can be represented
 Also known as IRA
 The last 4 bits for each digit (0-9) are identical to the binary representation of the
digit. E.g. XXX0111 represents 7 since ‘0111’ is 7 in binary
 The ASCII representation of space is 20h (h stands for hexadecimal)
 When one wants to convert an ASCII character (0-9) to tis numerical value, we can
simply subtract 30h from the ASCII encoding.



Shortcomings of ASCII that led to Unicode:
- ASCII can only store characters of the English language where Unicode can store
characters of numerous languages.
- Withaffecting ASCII only 128 characters can be represented, thus not all symbols
could be represented with ASCII. Unicode can represent much more characters.
- A document written in other code can’t be read by ASCII code and it will display
some characters instead of the content.
- Words like résumé can’t be expressed with ASCII since ASCII doesn’t allow for those
special characters.



Multicore processors

,Multicore is a method to improve processor performance wherein multiple processors are
placed on the same chip with a large shared cache. It provides the potential to increase
performance without increasing the clock rate.
Advantages include the following:

 Having a multi-core processor means it will work faster for certain programs (i.e.
programs that support it)
 The multi-core processors requires less power, because for small tasks only one or a
few cores will be uses instead of the entire processor.
 The signals between different CPUs travel shorter distances, therefore they degrade
less.




Portability in computer programming is the usability of the same software in
different environments, i.e. to use programs across different platforms (e.g.
computers and smart phones) and operating systems.




Components of the CPU:




Flash Memory
- Form of semiconductor memory
- Intermediate between EPROM and EEPROM in both cost and
functionality.

,Flash memory erasing technology
- Uses electrical erasing technology
- Entire flash memory can be erased in one or few seconds (faster then
EPROM)
- Possible to erase just blocks of memory rather than entire chip
- Section of memory cells are erased in a single action or “flash”
- Does not provide byte-level erasure.
- Uses only one transistor per bit
- Block of memory can be erased simultaneously.
- Is a form of RAM


Discuss flash memory erasing technology
Flash memory erasing technology makes use of Flash memory. Flash memory is
a form of semiconductor memory. Flash memory uses electrical erasing
technology. An entire flash of memory can be erased in one or two seconds,
which is much faster than EPROM. Flash memory gets its name because the
microchip is organized so that a section of memory cells are erased in a single
action or “flash”. Flash memory erasing technology doesn’t provide byte-level
erasure. It is possible to erase just blocks of memory rather than an entire chip.


Compare SRAM and DRAM
 SRAM is faster than DRAM. S is speed
 DRAM is available in larger storage capacity than SRAM. Obv since SRAM is faster
DRAM have higher capacity
 SRAM is more expensive than DRAM.
 Cache memory is an application of SRAM. In contrast DRAM is used in Main memory.
 The construction of SRAM is complex whilst DRAM is simple to design and
implement.
 DRAM is highly dense. In contrast SRAM is rarer.



Von Neumann Computer (also known as AIS computer)

,Why assembly language is important:




Disadvantages of writing programs in assembly language (p775)

,Advantages of writing programs in assembly languages

, More reasons:
- Code is often faster
- Insight into the problem often allows real improvements in performance
- It allows compete access to hardware
- Function libraries that are compatible with multiple compilers and Oss.


Relevance of assembly language in the future:
- In the future it could be used to understand how programs interact with
the OS, processor and the I/O system which could be useful for
developing cross-platform programs.
- It could be used to check how well a compiler optimizes a particular
piece of code.
- In the future it could be useful for coding hardware drivers and system
code, since accessing hardware may be difficult to access with High level
code.
- Useful for coding real-time systems