The Central Processing Unit
The central processing unit is the most important hardware component of a computer system. It is known as the CPU, the central processor or instruction processor, and the main microprocessor in a microcomputer.
The CPU can be divided into two major subunits which include:
1. Arithmetic-logic unit
2. Control unit
Computer Processing Speeds
How fast is fast? A person taking one step each nanosecond could circle the earth about 20 times in one second. Computer speeds are categorized as:
Milliseconds Speeds measured in thousands of a second
Microseconds Speeds measured in millionths of a second
Nanoseconds Speeds measured in billionths of a second
Picoseconds Speeds measured in trillionths of a second
MIPS Speeds measured in millions of instructions per second (MIPS).
MHz Speeds measured in millions of cycles per second (megahertz).
Processing speed depends on factors such as:
1. the size of circuitry paths (busses/wordsize)
2. the presence of high speed (cache) memory
3. the presence of specialized microprocessors (math coprocessor)
Primary & Secondary Storage
Primary Storage
The primary storage unit (main memory) holds data and instructions between processing steps and supplies them to the CU and ALU during processing. All data and programs must be placed into main memory before they can used in processed. The primary storage unit also holds data and program instructions between processing steps, and after processing is completed but before output. In modern computers, main memory consists of semiconductor memory chips. This includes RAM (random access memory) for loading programs and data before execution, and ROM (read only memory) for permanent programs that are supplied with the computer hardware.
Secondary Storage
Secondary storage is used for long term (permanent) storage of data and programs. Secondary storage devices include magnetic disks and tape units. Before the contents of secondary storage can be processed, they must be brought into the primary (main) storage unit.
Computer Storage Capacities
Data is processed and stored in a computer system through the presence or absence of electronic or magnetic "signals" in the computer's circuitry of in the media it uses. This is called a "two-state" or binary representation of data, since the computer and media can exhibit only two possible states or conditions.
Bit - the smallest element of data, (binary digit) which can have a value of zero or one. The capacity of memory chips is usually expressed in terms of bits.
Byte - is the basic grouping of bits that the computer operates as a single unit. It typically consists of 8 bits and is used to represent one character of data in most computer coding schemes (e.g. 8 bits = 1 byte) . The capacity of a computer's memory and secondary storage devices is usually expressed in terms of bytes.
Commonly used codes for representing characters in computer systems through various arrangements of bits are :
1. ASCII (American Standard Code for Information Exchange)
2. EBCDIC (Extended Binary Coded Decimal Interchange Code) Pronounced: EB SEE DICK
Kilobytes Is a measurement of storage capacity. Abbreviated as KB or K = one thousand bytes (1,024 or 210)
e.g. 640K = 640 x 1024 = 655,360 NOT 640,000
Megabytes Is a measurement of storage capacity. Abbreviated as MB or M = one million bytes (1,024 or 220)
Gigabyte Is a measurement of storage capacity. Abbreviated as GB or G = one billion bytes (1,024 or 230)
Terabyte Is a measurement of storage capacity. Abbreviated as TB or T = one trillion bytes ((1,024 or 240)
Types and Trends in Computers
Trends: Computer systems have evolved through several major stages or generations. Each generation is characterized by major changes in technology and processing power. As well, each generation has become smaller, faster, more reliable, and less costly to purchase and maintain.
source: Business Computing
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