Computer System Components

Input/output Controllers

Input/output controllers receive input and output requests from the central processor, and then send device-specific control signals to the device they control. They also manage the data flow to and from the device. This frees the central processor from involvment with the details of controlling each device. I/O controllers are needed only for those I/O devices that are part of the system.


Main Memory

kilobyte:	210 = 1024 bytes
megabyte:	220 = 1024 kilobytes
gigabyte:	230 = 1024 megabytes
terabyte:	240 = 1024 gigabytes

Addresses

Each byte of main storage has an address. Most modern processors use 32-bit addresses, so there are 2³² possible addresses. Think of main storage as if it were an array:

byte[0x00000000 ... 0xFFFFFFFF] mainStorage;

A main storage address is an index into memory. A 32-bit address is the address of a single byte. Thirty-two wires of the bus contain an address (there are many more bus wires for timing and control).

Virtual Memory




Cache Memory

Disk access is slow compared to RAM access. Potentially, using a combination of real memory and disk memory to implement the address space could greatly slow down program execution. However, with clever electronics and a good operating system, virtual memory is only slightly slower than physical memory.

Computer systems also have cache memory.

Contents of Memory

The memory system merely stores bit patterns. That some of these patterns represent integers, that some represent characters, and that some represent instructions (and so on) is of no concern to the electronics. How these patterns are used depends on the programs that use them.

End of the Chapter

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* The components of a computer system.
* Device controllers.
* Kilobytes, Megabytes, and Gigabytes
* Memory addresses
* Virtual memory.
* Cache memory