TOPIC 2 - Part 1 Flashcards
What is the relationship
between the components of a computer system?
A computer system accepts data or instructions as input from an input device. Data or instructions are then processed by the computer system.
It may be the case that other data or instructions, apart from the input, are necessary during processing. These exist in the storage and may be loaded and used. Finally, the computer system outputs the processed data into information that we can see and use. This output is also saved on the storage (memory).
CPU (processor or chip)
Data or instructions that are processed by a computer system in the process phase of the input, process, output and storage model are processed by the central processing unit (CPU). The CPU is a hardware component of a computer system and can perform basic arithmetic, logical or input/output operations, in order to process data from input devices into useful information. The CPU is the ”brain” of a computer system.
Components of CPU
. control unit (CU)
. arithmetic logic unit (ALU)
. memory address register (MAR)
. memory data register (MDR)
What are the functions of the control unit?
The control unit (CU) is responsible for the operation of the CPU. It controls the retrieval of instructions from the primary memory as well as the sequence of their execution.
What are the functions of the arithmetic logic unit (ALU)?
The arithmetic logic unit (ALU) performs all the basic arithmetic, logical or input/output
operations. The CU is responsible for providing the ALU with the data that needs to be processed as well as the instructions of how the data should be processed.
What are two types of primary memories?
The primary memory used as storage contains two types of memory - the random access memory (RAM) and the read only memory (ROM).
RAM
The RAM stores the executing program instructions as well as any data that is needed. Instructions and data in the RAM are stored in unique memory locations and every such location has an address as well as content. The content is where the instructions and data reside, whereas the memory location is used by the CU to find, retrieve and access the data in order to send it to the ALU for processing.
RAM is a general—purpose storage area
meaning that the data stored can be over—
written. This allows data and instructions to
be loaded for execution and use whenever
they are necessary. However, RAM is
volatile, which means that whenever power
is lost the contents of its memory are wiped.
ROM
Similar to the RAM, the ROM holds instructions and data in unique memory locations. Every such location has an address as well as content. Unlike the RAM however, the ROM is used to store permanent instructions and data that cannot be changed and are used to boot and operate the computer. As such, nothing can be altered in the ROM.
ROM is used to store instructions and data and cannot be over—written. This means that the instructions that are embedded in ROM cannot be changed, even if power is lost, and as such is considered nonvolatile memory. ROM is used to store programs and instructions that do not need to be updated or change.
Registers
The CU contains various registers. In general, a register is a small storage location that can hold data, usually a multiple of 8 bits. The size of the register in bytes is known as a word. The basic registers in the CU are the memory address register (MAR) and the memory data register (MDR).
MAR
The MAR holds the memory address of the data to be used by the ALU, so that the ALU can fetch the corresponding content from the memory and process it accordingly. The MAR may also hold the memory address of where data that has been processed will need to be stored. In order for the MAR to communicate with the primary memory, a connection is necessary. This connection is accomplished by the Memory (Address) Bus.
MDR
The MDR holds the data that is to be used by the ALU and then saved to the RAM. The MDR
is closely related to the MAR, since whichever memory address location the MAR is holding,
the corresponding data will be loaded onto the MDR for processing by the ALU. After the
processing has taken place, the ALU places the result onto the MDR and the data is copied to the memory address location in RAM specified by the MAR. The connection between the RAM and the MDR is accomplished by the Data Bus.
Primary memory
The primary memory is the only storage that is directly accessible by the CPU. At any point in time, the primary memory may hold both data and instructions that are currently running on the computer system. These data and instructions are stored in the primary memory as binary machine code (i.e. a series of 0 s and 1s).
2 main types of RAM and cache memory
RAM has two main types:
. Dynamic RAM (DRAM)
. Static RAM (SRAM)
SRAM is faster but more expensive than DRAM, and as such DRAM is preferred for the main RAM of a computer system. However, a small amount of SRAM is placed between the main RAM and the processor and it is called cache. As such, cache is a smaller and
faster RAM (SRAM) that temporarily stores instructions and data so that the processor does not need to access the slower main memory (DRAM).
How does cache memory work?
Cache holds the information from the RAM that is most actively used, and accessed most frequently. The computer system will run faster as the slower main memory will need to be accessed less frequently. When the processor needs to read from the main memory, it first checks if a copy of the data exists in the cache. If so, the processor reads from the cache, instead of reading from main memory. This action speeds up the process. If the data to be read do not exist in the cache, the data are first copied to the cache and then used. When the processor needs to write to the main memory it does so through cache memory.
Two types of cache memory
There are two types of cache memories that reside between the main RAM and the processor. These two types are L1 cache and L2 cache. L1 cache is placed on the microprocessor itself whereas L2 cache is placed between the primary memory and the microprocessor.
